Understanding AHS Plant Heat Zones

What are AHS Plant Heat Zones? They're the counterpart to USDA Plant Hardiness Zones. USDA Plant Hardiness Zones are based on average cold temperatures of winter and the AHS Plant Heat Zones are based on average hot temperatures of summer. Hardiness Zones help gardeners determine if a plant can survive their region's winter extreme temperatures while Heat Zones help determine if a plant can survive their summer extreme temperatures.

The American Horticultural Society coordinated with the same people who helped develop the USDA Hardiness Zone map to develop a Heat Zone map based on temperature data from the National Climactic Data Center. Daily high temperatures from National Weather Service stations throughout the United States were compiled for the years 1974 through  1995. In 1997 they produced a national map representing their findings.

The result is a map that color codes the country into 12 zones that indicate the average number of days when the temperature is above 86F degrees (30C). These are "heat days". Zone 1 has an average of less than one day per year above 86 degrees while Zone 12 has an average of more than 210 days above 86 degrees.

Why 86F (30C) degrees? That is the point that many plants begin to experience distress and potential damage from sustained heat. Above this point plants can drop blossoms, drop leaves, fade in color, reduce fruit development, and possibly die. Some plants won't die right away but will be stressed for so long that each year they perform less productively than the year before.

Many plants will wilt in heat, but will recover once temperatures fall. Sustained heat can have a serious physiological impact on some plants and triggers a lingering decline to ultimate death. Knowing how a plant will handle hot days is the reason for the AHS Heat Zone Map.

Most gardeners are familiar with the USDA Hardiness Zone system and look for the number on a plant tag when selecting new plantings. I live in Zone 5 and always make sure new perennial plants are at least hardy down to -20F degrees that the zone represents. I prefer plants hardy to Zone 4 for the occasional extremely low temperatures we get that approach -30F in winter.

I'm in AHS Plant Heat Zone 5. That represents 30 to 45 days above 86F degrees. I prefer to select plants for at least Zone 6 for the recent hot summers we've had; Zone 6 allows for 45 to 60 days above 86F. This year we're definitely encroaching on Zone 6 heat days.

Plant growers and distributors that include AHS Plant Heat Zones on tags will list both zone ranges. You'll now find a listing like "3-9, 6-1". That means the plant is suitable for USDA Hardiness Zones 3 through 9 and is suitable for AHS Heat Zones 6 through 1. Many plant catalogs are also including this information in their plant descriptions.

For me, an ideal plant would be something like "4-9, 7-1". That means it can handle the cold of the Hardiness Zone 4 and the heat of Heat Zone 7. My garden is well within both ranges and the plant should do well.

There are some limitations with the AHS Heat Zone map. Because it is relatively new and unknown, there aren't many resources available to make it easy for you to identify your zone. You have to try and determine exactly where your city falls within the zones on the national map. Apparently the AHS had a tool for determining exact locations, but the zone finder application is nowhere to be found now. I haven't been able to find any other source for finding Heat Zones by zip code like the USDA map has.

You can look at the map at: http://www.ahs.org/gardening-resources/gardening-maps/heat-zone-map

At gardening resources.com I found a breakdown of the Heat Zones by state, which was a little easier to read. You can find it here: http://www.gardeningplaces.com/heatzonemap/

Over 15,000 plants have been coded for heat tolerance. As more plants are coded and more companies begin listing both USDA and AHS zones on plant information, you can expect more gardeners to become familiar and comfortable with the conversion to a two-zone system.

For many of us we choose our plants, put them in our gardens, and then see how they do. For various reasons some plants do well while others struggle. Using both zone maps for selecting plants can help us put in plants that will not only grow well, but will thrive.

If some of your plants didn't do well in summer it may be because they weren't able to tolerate your garden's hot days. That may be an indication that they're inappropriate for your region. Understanding and using the AHS Heat Zones can help prevent similar problems in the future.

Link to the AHS Heat Zone map: http://www.ahs.org/gardening-resources/gardening-maps/heat-zone-map

Link to gardeningplaces.com state maps: http://www.gardeningplaces.com/heatzonemap/

What are AHS Plant Heat Zones? They're the counterpart to USDA Plant Hardiness Zones. USDA Plant Hardiness Zones are based on average cold temperatures of winter and the AHS Plant Heat Zones are based on average hot temperatures of summer. Hardiness Zones help gardeners determine if a plant can survive their region's winter extreme temperatures while Heat Zones help determine if a plant can survive their summer extreme temperatures.

The American Horticultural Society coordinated with the same people who helped develop the USDA Hardiness Zone map to develop a Heat Zone map based on temperature data from the National Climactic Data Center. Daily high temperatures from National Weather Service stations throughout the United States were compiled for the years 1974 through  1995. In 1997 they produced a national map representing their findings.

The result is a map that color codes the country into 12 zones that indicate the average number of days when the temperature is above 86F degrees (30C). These are "heat days". Zone 1 has an average of less than one day per year above 86 degrees while Zone 12 has an average of more than 210 days above 86 degrees.

Why 86F (30C) degrees? That is the point that many plants begin to experience distress and potential damage from sustained heat. Above this point plants can drop blossoms, drop leaves, fade in color, reduce fruit development, and possibly die. Some plants won't die right away but will be stressed for so long that each year they perform less productively than the year before.

Many plants will wilt in heat, but will recover once temperatures fall. Sustained heat can have a serious physiological impact on some plants and triggers a lingering decline to ultimate death. Knowing how a plant will handle hot days is the reason for the AHS Heat Zone Map.

Most gardeners are familiar with the USDA Hardiness Zone system and look for the number on a plant tag when selecting new plantings. I live in Zone 5 and always make sure new perennial plants are at least hardy down to -20F degrees that the zone represents. I prefer plants hardy to Zone 4 for the occasional extremely low temperatures we get that approach -30F in winter.

I'm in AHS Plant Heat Zone 5. That represents 30 to 45 days above 86F degrees. I prefer to select plants for at least Zone 6 for the recent hot summers we've had; Zone 6 allows for 45 to 60 days above 86F. This year we're definitely encroaching on Zone 6 heat days.

Plant growers and distributors that include AHS Plant Heat Zones on tags will list both zone ranges. You'll now find a listing like "3-9, 6-1". That means the plant is suitable for USDA Hardiness Zones 3 through 9 and is suitable for AHS Heat Zones 6 through 1. Many plant catalogs are also including this information in their plant descriptions.

For me, an ideal plant would be something like "4-9, 7-1". That means it can handle the cold of the Hardiness Zone 4 and the heat of Heat Zone 7. My garden is well within both ranges and the plant should do well.

There are some limitations with the AHS Heat Zone map. Because it is relatively new and unknown, there aren't many resources available to make it easy for you to identify your zone. You have to try and determine exactly where your city falls within the zones on the national map. Apparently the AHS had a tool for determining exact locations, but the zone finder application is nowhere to be found now. I haven't been able to find any other source for finding Heat Zones by zip code like the USDA map has.

You can look at the map at: http://www.ahs.org/gardening-resources/gardening-maps/heat-zone-map

At gardening resources.com I found a breakdown of the Heat Zones by state, which was a little easier to read. You can find it here: http://www.gardeningplaces.com/heatzonemap/

Over 15,000 plants have been coded for heat tolerance. As more plants are coded and more companies begin listing both USDA and AHS zones on plant information, you can expect more gardeners to become familiar and comfortable with the conversion to a two-zone system.

For many of us we choose our plants, put them in our gardens, and then see how they do. For various reasons some plants do well while others struggle. Using both zone maps for selecting plants can help us put in plants that will not only grow well, but will thrive.

If some of your plants didn't do well in summer it may be because they weren't able to tolerate your garden's hot days. That may be an indication that they're inappropriate for your region. Understanding and using the AHS Heat Zones can help prevent similar problems in the future.

Link to the AHS Heat Zone map: http://www.ahs.org/gardening-resources/gardening-maps/heat-zone-map

Link to gardeningplaces.com state maps: http://www.gardeningplaces.com/heatzonemap/

Sow Cool Season Plants in Summer for a Fall Crop

Two harvests in the same growing season are easy to accomplish. Many gardeners sow and plant in spring, spend summer tending to their crops, harvest in early fall, and then wrap it all up and wait until spring to repeat the same process. With little effort you can double your garden's output with sow, tend, sow, harvest, tend, and then harvest again. Then you can spend winter satisfied that your garden played double duty to produce all it could.

Chard is a great fall crop

In late summer you sow seeds for cool season plants that will grow as temperatures begin to decline. They'll be ready to harvest after the first frosts have appeared and long after the last tomatoes were pulled from the vines. There is no need to create new gardens; you use the same beds you do now.

Cool season crops are primarily the ones that provide leaves, stems, and roots for harvest. These crops include:

Arugula, beets, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, celery, chard, collards, endive, fennel, kale, kohrabi, leeks, lettuce, mustard greens, onions, peas, parsnips, potatoes, radishes, spinach, turnips

Peas, especially snow peas, are good in fall

Many gardeners grow these plants in spring and hope for a slow start to summer so the plants will mature and be ready for harvest before high heat causes them to bolt and their taste turns bitter. We take advantage of their natural ability to tolerate low temperatures by planting early.

We can also use that ability to plant late. The mature plant tolerates the low temperatures of fall, there is no risk of bolting, and many people believe many of these crops taste superior after exposure to frost.

Those of us who sow in early spring and hope the soil has warmed enough to initiate germination are ready for a percentage of our seeds to never grow. Those of us who sow in late summer are pleased that the warm soil provides speedy germination with little seed loss.

Early seed and plant care is different when you plant late. In spring there is less need for extra watering; lower temperatures mean less evaporation and there is always a chance of rain or late snow. In summer, the heat requires more gardener attention to maintaining moist soil conditions for seeds and young plants; you may need to mist or water the plants two or three times a day in harsh sun.

Temperatures above 80F (27C) will cause broccoli and spinach to bolt quickly. Sowing in a shady spot or setting up a row cover can reduce this concern.

Once the plants have a few sets of leaves the need for watering becomes less than in late summer. While early plants need more water to combat the increasing summer heat, later plants require less water as the decreasing temperatures bring comfort. The plants are less stressed in fall. They grow in the conditions they like best; they're called cool season plants for a reason.

As long as the day temperatures remain about 10 to 15 degrees above freezing (40F - 50F, 4C - 10C) you can expect the crops to continue growing and producing. When the day temps remain below 40F (4C) the plants may begin to suffer. Careful harvesting will still produce results. The center of the plant may still have new, tasty leaves while the exterior leaves look frazzled.

Hard freezes, cold days, and icy conditions will adversely affect most cool season crops and will spell the end for your second harvest, but you can delay winter by mulching heavily with straw and using a season extender like cold frames, cloches, or plastic tunnels. I use my hoophouse system to harvest well into November and even December.

Broccoli and beets ready for overnight protection

Some crops like cabbage, kale, and spinach can do well, even in snow. With heavy mulching, beets, leeks, and parsnips can often be overwintered and harvested in spring (I've done this). 

Use your entire vegetable garden for fall planting. If you have a cool-season spring bed for broccoli, spinach, or lettuce and then let that bed remain filled with bolty, straggly, dried plants throughout the summer, rip those plants out and sow again for a fall crop.

Your tomatoes, peppers, and melons will decline in cooling weather. Anticipate their decline and sow seeds among those plants, in the same beds. When the first frost zaps your tomato plant, cut it out and let the cabbage and broccoli growing nearby overtake that space.

Root crops won't be as big as spring plantings, but may be tastier. Try growing small, thumb-sized carrot varieties or harvest them young before the ground freezes. Beet roots will be harvested when they're just a few inches big, but the beet leaves can be harvested continually.

Beet leaves are edible and tasty

Garden pests can be less of a concern for a fall garden. Many insect pests are less active, if not gone, in fall. The weeds will spend all summer attacking aren't active in fall. Even deer seem to be scarce as they make their way to find a winter bed.

While growing a second crop in the same season sounds like extra work, it doesn't need to be. Summer garden beds should be cleaned up before winter so insects don't have a place to overwinter. That clean up works well to prepare the beds for fall crops.

You'll spend a few more days in the garden watering and harvesting, but is that really a bad thing? Fall gardening allows you to do more of what you like and for me that's a good thing.

Link to "Extending Your Growing Season with Mini Greenhouses"

Two harvests in the same growing season are easy to accomplish. Many gardeners sow and plant in spring, spend summer tending to their crops, harvest in early fall, and then wrap it all up and wait until spring to repeat the same process. With little effort you can double your garden's output with sow, tend, sow, harvest, tend, and then harvest again. Then you can spend winter satisfied that your garden played double duty to produce all it could.

Chard is a great fall crop

In late summer you sow seeds for cool season plants that will grow as temperatures begin to decline. They'll be ready to harvest after the first frosts have appeared and long after the last tomatoes were pulled from the vines. There is no need to create new gardens; you use the same beds you do now.

Cool season crops are primarily the ones that provide leaves, stems, and roots for harvest. These crops include:

Arugula, beets, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, celery, chard, collards, endive, fennel, kale, kohrabi, leeks, lettuce, mustard greens, onions, peas, parsnips, potatoes, radishes, spinach, turnips

Peas, especially snow peas, are good in fall

Many gardeners grow these plants in spring and hope for a slow start to summer so the plants will mature and be ready for harvest before high heat causes them to bolt and their taste turns bitter. We take advantage of their natural ability to tolerate low temperatures by planting early.

We can also use that ability to plant late. The mature plant tolerates the low temperatures of fall, there is no risk of bolting, and many people believe many of these crops taste superior after exposure to frost.

Those of us who sow in early spring and hope the soil has warmed enough to initiate germination are ready for a percentage of our seeds to never grow. Those of us who sow in late summer are pleased that the warm soil provides speedy germination with little seed loss.

Early seed and plant care is different when you plant late. In spring there is less need for extra watering; lower temperatures mean less evaporation and there is always a chance of rain or late snow. In summer, the heat requires more gardener attention to maintaining moist soil conditions for seeds and young plants; you may need to mist or water the plants two or three times a day in harsh sun.

Temperatures above 80F (27C) will cause broccoli and spinach to bolt quickly. Sowing in a shady spot or setting up a row cover can reduce this concern.

Once the plants have a few sets of leaves the need for watering becomes less than in late summer. While early plants need more water to combat the increasing summer heat, later plants require less water as the decreasing temperatures bring comfort. The plants are less stressed in fall. They grow in the conditions they like best; they're called cool season plants for a reason.

As long as the day temperatures remain about 10 to 15 degrees above freezing (40F - 50F, 4C - 10C) you can expect the crops to continue growing and producing. When the day temps remain below 40F (4C) the plants may begin to suffer. Careful harvesting will still produce results. The center of the plant may still have new, tasty leaves while the exterior leaves look frazzled.

Hard freezes, cold days, and icy conditions will adversely affect most cool season crops and will spell the end for your second harvest, but you can delay winter by mulching heavily with straw and using a season extender like cold frames, cloches, or plastic tunnels. I use my hoophouse system to harvest well into November and even December.

Broccoli and beets ready for overnight protection

Some crops like cabbage, kale, and spinach can do well, even in snow. With heavy mulching, beets, leeks, and parsnips can often be overwintered and harvested in spring (I've done this). 

Use your entire vegetable garden for fall planting. If you have a cool-season spring bed for broccoli, spinach, or lettuce and then let that bed remain filled with bolty, straggly, dried plants throughout the summer, rip those plants out and sow again for a fall crop.

Your tomatoes, peppers, and melons will decline in cooling weather. Anticipate their decline and sow seeds among those plants, in the same beds. When the first frost zaps your tomato plant, cut it out and let the cabbage and broccoli growing nearby overtake that space.

Root crops won't be as big as spring plantings, but may be tastier. Try growing small, thumb-sized carrot varieties or harvest them young before the ground freezes. Beet roots will be harvested when they're just a few inches big, but the beet leaves can be harvested continually.

Beet leaves are edible and tasty

Garden pests can be less of a concern for a fall garden. Many insect pests are less active, if not gone, in fall. The weeds will spend all summer attacking aren't active in fall. Even deer seem to be scarce as they make their way to find a winter bed.

While growing a second crop in the same season sounds like extra work, it doesn't need to be. Summer garden beds should be cleaned up before winter so insects don't have a place to overwinter. That clean up works well to prepare the beds for fall crops.

You'll spend a few more days in the garden watering and harvesting, but is that really a bad thing? Fall gardening allows you to do more of what you like and for me that's a good thing.

Link to "Extending Your Growing Season with Mini Greenhouses"

Plant a Fall Crop

Sowing and planting in summer is a great way to get the most out of your garden space. I just sowed beets and broccoli in early August and will be able to squeeze in another crop of vegetables before winter snow and hard freezes put an end to my growing season. The plants mature in fall and provide a nice second harvest. This fall crop allows a garden to produce a full second season.

Beets are a nice fall crop

My lettuce and spinach beds were pretty well spent after the plants bolted and went to seed. Many gardeners would clean up those beds and let them lie fallow until spring, but I used that space to plant another crop. That essentially doubles my garden output without increasing its overall size.

The key is understanding the difference between cool season and warm season garden plants. Cool season plants are the ones we usually plant in spring. They include cabbage, lettuce, spinach, kale, peas, radish, beets, and chard. These plants can handle an occasional bout with cold temperatures. Warm season plants are the ones we plant after the last frost date. They include tomatoes, peppers, vine squash, and melons. When those plants experience frost they shrivel and die.

We can sow cool season plant seeds in early spring because the young plants aren't killed by late frost. Many gardeners know that it takes awhile for many of those seeds to germinate because of cold soil temperatures. When they do begin to grow, their productive season can be short because the heat of summer tends to affect them adversely and they flower, go to seed, and fade quickly.

Sowing these same seeds in late summer results in quick germination in the warm soil. There is no cold threat to the young plants and they grow quickly. As they mature and begin to fruit an occasional early frost may threaten, but the larger plants can shrug it off easily. There is absolutely no threat of high temperatures causing the plant to bolt so they produce fruit until they die.

That's one of the greatest advantages to planting a fall crop:  the production of fruit is often longer and greater than spring crops. These plants often relish the cool temperatures and rather than respond poorly to hot days they respond richly to cold days. Many people think these plants produce tastier produce after they've been exposed to cold.

Treat your second season garden just as you would a spring one. Before planting, amend the soil and prepare the bed. A good dose of compost or aged manure is a nice boost to soil that has already been used for a recent crop. You usually have plenty of time to do this from when the plants fade in mid summer to when you plant in late summer.

I amended one bed with biochar

Mulch becomes an important factor in the success of a fall crop. Mulch moderates soil temperature. In a spring planting for summer harvest, the mulch helps keep the soil from getting too warm. In a summer planting for fall harvest, the mulch helps keep the soil from getting too cool.

Be aware of different irrigation needs than you may be used to. The seedlings and young plants are beginning to grow when it's still hot out. A new spring bed may need watering twice a day to keep the soil moist. A new summer bed may need watering four or five times a day to stay moist. To help keep the soil from drying out quickly, I drape fabric over the bed to shade the soil until the plants establish themselves and the days begin to cool. Row covers and shade cloth are ideal.

Recycled patio umbrella for shade

Once the plants mature, their water needs will be less than the same plants in early summer. In the cooler days of fall, there is less evaporation and water loss due to transpiration. Mulch can mask the true level of soil moisture so be sure to physically check the soil before you water. Over watering and drowning roots is common in second season gardens.

Be ready for different growing characteristics. When I sowed beet seeds in spring it took almost two weeks for the first sprouts to appear; even cool season plants need the soil temperature to be warm enough to effectively germinate. The beet seeds I sowed in summer germinated after four days.

Many root crops are well suited as second season crops. Carrots, turnips, parsnips, beets, and radishes do well when planted up to two months before the first frost. For me that's early August, but for many gardeners that time extends into September or October. A thick mulch helps keep the ground from freezing early and affecting the growth and harvest of the roots.

Cabbage, green onions, spinach, cauliflower, snap and snow peas, should be planted a little earlier to ensure they complete their growth before cold sets in. For me that was mid July, but for many gardeners that time is now.

Tough greens like endive, mustard, chard, spinach can handle cold well. Chard, in particular, grows in snow and has a nice sweet flavor as a result.

Second season gardens offer advantages that are easy to overlook. The cooler temperatures affect weeds and garden pests too. Less weeding and pest management chores are definitely welcomed by most gardeners. Often, it isn't until you're reviewing the success of your growing season with the snows falling that you realize how easy the fall crop was to maintain.

When you use a method for extending your growing season you may be able to harvest vegetables well into December and winter. (Check out my March 2, 2011, article "Extending Your Growing Season With Mini Greenhouses").

Some of these cool season plants will continue to survive even in the harshest winters. I left my leeks, onions, shallots, beets, and parsnips in the ground through the winter. They all came back and began greening again when the spring warmth returned. The leeks and parsnips that had a winter to rest were twice the size of ones harvested before the ground froze hard.

Thick mulch helped these leeks and shallots overwinter

If you're interested in a second fall crop but don't want extra effort, just let your spring crops go to seed. My spinach, arugala, radish, and lettuce plants flowered, went to seed, browned, and faded. I collected some of the seeds and pulled the plants. Many of the seeds that scattered on the ground have sprouted and are ready to give me a second harvest. It helped that I amended and turned over the soil in those spots for the beets and broccoli, and I'm willing to let the volunteers share the same bed.

Not all seeds germinate in the beds

Whether planned or by accident, take advantage of the growth characteristics of cool season plants and enjoy a second season. Grow a fall crop.


Link to "Extending Your Growing Season With Mini Greenhouses"

Sowing and planting in summer is a great way to get the most out of your garden space. I just sowed beets and broccoli in early August and will be able to squeeze in another crop of vegetables before winter snow and hard freezes put an end to my growing season. The plants mature in fall and provide a nice second harvest. This fall crop allows a garden to produce a full second season.

Beets are a nice fall crop

My lettuce and spinach beds were pretty well spent after the plants bolted and went to seed. Many gardeners would clean up those beds and let them lie fallow until spring, but I used that space to plant another crop. That essentially doubles my garden output without increasing its overall size.

The key is understanding the difference between cool season and warm season garden plants. Cool season plants are the ones we usually plant in spring. They include cabbage, lettuce, spinach, kale, peas, radish, beets, and chard. These plants can handle an occasional bout with cold temperatures. Warm season plants are the ones we plant after the last frost date. They include tomatoes, peppers, vine squash, and melons. When those plants experience frost they shrivel and die.

We can sow cool season plant seeds in early spring because the young plants aren't killed by late frost. Many gardeners know that it takes awhile for many of those seeds to germinate because of cold soil temperatures. When they do begin to grow, their productive season can be short because the heat of summer tends to affect them adversely and they flower, go to seed, and fade quickly.

Sowing these same seeds in late summer results in quick germination in the warm soil. There is no cold threat to the young plants and they grow quickly. As they mature and begin to fruit an occasional early frost may threaten, but the larger plants can shrug it off easily. There is absolutely no threat of high temperatures causing the plant to bolt so they produce fruit until they die.

That's one of the greatest advantages to planting a fall crop:  the production of fruit is often longer and greater than spring crops. These plants often relish the cool temperatures and rather than respond poorly to hot days they respond richly to cold days. Many people think these plants produce tastier produce after they've been exposed to cold.

Treat your second season garden just as you would a spring one. Before planting, amend the soil and prepare the bed. A good dose of compost or aged manure is a nice boost to soil that has already been used for a recent crop. You usually have plenty of time to do this from when the plants fade in mid summer to when you plant in late summer.

I amended one bed with biochar

Mulch becomes an important factor in the success of a fall crop. Mulch moderates soil temperature. In a spring planting for summer harvest, the mulch helps keep the soil from getting too warm. In a summer planting for fall harvest, the mulch helps keep the soil from getting too cool.

Be aware of different irrigation needs than you may be used to. The seedlings and young plants are beginning to grow when it's still hot out. A new spring bed may need watering twice a day to keep the soil moist. A new summer bed may need watering four or five times a day to stay moist. To help keep the soil from drying out quickly, I drape fabric over the bed to shade the soil until the plants establish themselves and the days begin to cool. Row covers and shade cloth are ideal.

Recycled patio umbrella for shade

Once the plants mature, their water needs will be less than the same plants in early summer. In the cooler days of fall, there is less evaporation and water loss due to transpiration. Mulch can mask the true level of soil moisture so be sure to physically check the soil before you water. Over watering and drowning roots is common in second season gardens.

Be ready for different growing characteristics. When I sowed beet seeds in spring it took almost two weeks for the first sprouts to appear; even cool season plants need the soil temperature to be warm enough to effectively germinate. The beet seeds I sowed in summer germinated after four days.

Many root crops are well suited as second season crops. Carrots, turnips, parsnips, beets, and radishes do well when planted up to two months before the first frost. For me that's early August, but for many gardeners that time extends into September or October. A thick mulch helps keep the ground from freezing early and affecting the growth and harvest of the roots.

Cabbage, green onions, spinach, cauliflower, snap and snow peas, should be planted a little earlier to ensure they complete their growth before cold sets in. For me that was mid July, but for many gardeners that time is now.

Tough greens like endive, mustard, chard, spinach can handle cold well. Chard, in particular, grows in snow and has a nice sweet flavor as a result.

Second season gardens offer advantages that are easy to overlook. The cooler temperatures affect weeds and garden pests too. Less weeding and pest management chores are definitely welcomed by most gardeners. Often, it isn't until you're reviewing the success of your growing season with the snows falling that you realize how easy the fall crop was to maintain.

When you use a method for extending your growing season you may be able to harvest vegetables well into December and winter. (Check out my March 2, 2011, article "Extending Your Growing Season With Mini Greenhouses").

Some of these cool season plants will continue to survive even in the harshest winters. I left my leeks, onions, shallots, beets, and parsnips in the ground through the winter. They all came back and began greening again when the spring warmth returned. The leeks and parsnips that had a winter to rest were twice the size of ones harvested before the ground froze hard.

Thick mulch helped these leeks and shallots overwinter

If you're interested in a second fall crop but don't want extra effort, just let your spring crops go to seed. My spinach, arugala, radish, and lettuce plants flowered, went to seed, browned, and faded. I collected some of the seeds and pulled the plants. Many of the seeds that scattered on the ground have sprouted and are ready to give me a second harvest. It helped that I amended and turned over the soil in those spots for the beets and broccoli, and I'm willing to let the volunteers share the same bed.

Not all seeds germinate in the beds

Whether planned or by accident, take advantage of the growth characteristics of cool season plants and enjoy a second season. Grow a fall crop.


Link to "Extending Your Growing Season With Mini Greenhouses"

Microclimates in the Garden

Microclimates give gardeners an opportunity to grow plants that might not normally be successful in their landscape. Microclimates can also spell doom for plants that should grow well. As in the real estate game, in gardening it's all about location, location, location.

Every yard has spots that react differently to weather factors

A microclimate is a geographical area with a different climate than the larger area surrounding it. The effect of localized weather varies in microclimates. Some microclimates cover miles of territory, but for our garden discussion we're talking about garden spots that may only be a few feet wide. Every season offers the opportunity to find microclimates in your garden (see my articles: "Look for Microclimates in the Garden", Jan 13, 2011; and "Microclimates in Summer", July 8, 2011). Spring is a good time to try and identify some of the microclimates in your garden that you may not notice at other times.

Gardening is a long-term activity and by noting changes in your garden throughout the year you can use your time and effort to provide the best environment for your plants. Microclimates exist everywhere but until you notice their effects on you and your plants you may be wasting valuable resources.

Some microclimates are obvious. Maybe there's a spot in your yard that is always high and dry; snow melts first in that spot, grass dries out and needs more water in that spot, or maybe every shrub you plant dies in that spot. Pausing for a little analysis may reveal it is always sunny, windy, and exposed. That's a microclimate.

On the other end of the spectrum think about the garden bed that is always wet and cold. Maybe its a low spot under some trees that never sees sun and never dries out; maybe it's the spot that always has the last pile of snow in spring. That's a microclimate.

These two microclimates may exist mere feet from each other but to plants they may as well be separated by miles. A plant that can grow in one of them can't grow in the other. It's up to you the gardener to recognize the differences and act accordingly.

My wife and I have noticed an interesting microclimate in our yard. We have three stands of Aspens that are each only separated by about 50 or 60 feet (15-18 meters). The stand in the front yard always buds out first. Two or three weeks later as those trees have full leaves, the second stand begins to show signs of green. Another two or three weeks go by before the third stand finally begins to leaf out.

Full leaves on the right, new leaves in the middle, no leaves on the left

An analysis of the landscape reveals a minor grade in the landscape; the last Aspen stand to grow is in the lowest elevation. The upper stand also gets a little more sunshine; the lower stand is shaded by trees and the house late in the day. It's also likely that the lower stand is more exposed to wind, common in the spring; the two upper stands have some wind protection from nearby structures and other trees.

The bare trees on the left are noticeably lower in elevation

Recognizing this microclimate is important to my gardening and plant selection. And I've made mistakes by not analyzing it earlier. Initially I planted Irises under the trees in the lower stand. They get full sun in early spring before the trees leaf out and I thought that would be enough for their success. The problem comes in autumn. As you might guess, the upper Aspen stands drop their leaves first and this lower stand is the last to lose leaves in fall. That means that the Irises are still shaded when they should be getting sun to nourish their rhizomes. I never get the flowers I should because the Iris rhizomes aren't nourished by sunlight as well as they should be.

This microclimate analysis changed my approach to plant selection. First, I planted new lavender plants near the upper Aspen stand. The slightly improved sun exposure helped those lavender plants grow better than others in the back yard. This year I've planted Coral Bells (Heuchera) in that lower spot. Coral Bells like sun when it's cold and some shade when it's hot, exactly what the location offers.

Without a microclimate analysis I might spend years fertilizing and babying the Irises and other plants that were never really suited for that garden bed. Now I can focus on the proper plants for better success.

Another microclimate, that I created, is evident in my stone patio. I wanted a spot to support the growing requirements of lavender and other high desert plants. I chose a location that gets full sun and build a raised, stone patio. It is now the spot that warms quickly in spring and where snow melts first. The lavender, sedum, thyme, and iceplants are thriving in a spot designed for them.

The warmer stone helps nearby plants in early spring

I chose a nice location with full sun for my vegetable garden. But even in this select area microclimates exist. The raised beds are built on a slope and the upper beds are a few feet higher in elevation than the lower. The upper beds have more exposure to wind and receive late-day shade before the others. Last year tomato plants in the lower beds did better than tomato plants just a few feet away; the wind and shade made a difference even though it is barely noticeable to me. The plants obviously noticed.

A slope with trees can create many microclimates

Look at how your garden wakes up in spring. Note the different growth rates of plants just a few feet apart. Spot elevation, sun, and wind variations in your landscape. Take a few minutes to analyze why some plants do well while others struggle.

By thinking about microclimates in your garden and acting to match plants with the best growing environment you can improve your garden's success. We often don't think much about a minor difference in temperature, sun, or shade, but to tender plants it can mean the difference between life and death.

Before you put new plants in a garden bed and before you sow seeds notice the year-round characteristics of that spot of ground. It may be perfect for young plants in the spring but does it offer the best environment and microclimate later in the plant's life cycle? The best gardening practices look into the future. It may sound difficult but it begins by thinking about how little differences in localized climate exists from one section of your garden to another. By spotting these changes you can use microclimates to your advantage.

Link to:

"Look for Microclimates in the Garden"
"Microclimates in Summer"

Microclimates give gardeners an opportunity to grow plants that might not normally be successful in their landscape. Microclimates can also spell doom for plants that should grow well. As in the real estate game, in gardening it's all about location, location, location.

Every yard has spots that react differently to weather factors

A microclimate is a geographical area with a different climate than the larger area surrounding it. The effect of localized weather varies in microclimates. Some microclimates cover miles of territory, but for our garden discussion we're talking about garden spots that may only be a few feet wide. Every season offers the opportunity to find microclimates in your garden (see my articles: "Look for Microclimates in the Garden", Jan 13, 2011; and "Microclimates in Summer", July 8, 2011). Spring is a good time to try and identify some of the microclimates in your garden that you may not notice at other times.

Gardening is a long-term activity and by noting changes in your garden throughout the year you can use your time and effort to provide the best environment for your plants. Microclimates exist everywhere but until you notice their effects on you and your plants you may be wasting valuable resources.

Some microclimates are obvious. Maybe there's a spot in your yard that is always high and dry; snow melts first in that spot, grass dries out and needs more water in that spot, or maybe every shrub you plant dies in that spot. Pausing for a little analysis may reveal it is always sunny, windy, and exposed. That's a microclimate.

On the other end of the spectrum think about the garden bed that is always wet and cold. Maybe its a low spot under some trees that never sees sun and never dries out; maybe it's the spot that always has the last pile of snow in spring. That's a microclimate.

These two microclimates may exist mere feet from each other but to plants they may as well be separated by miles. A plant that can grow in one of them can't grow in the other. It's up to you the gardener to recognize the differences and act accordingly.

My wife and I have noticed an interesting microclimate in our yard. We have three stands of Aspens that are each only separated by about 50 or 60 feet (15-18 meters). The stand in the front yard always buds out first. Two or three weeks later as those trees have full leaves, the second stand begins to show signs of green. Another two or three weeks go by before the third stand finally begins to leaf out.

Full leaves on the right, new leaves in the middle, no leaves on the left

An analysis of the landscape reveals a minor grade in the landscape; the last Aspen stand to grow is in the lowest elevation. The upper stand also gets a little more sunshine; the lower stand is shaded by trees and the house late in the day. It's also likely that the lower stand is more exposed to wind, common in the spring; the two upper stands have some wind protection from nearby structures and other trees.

The bare trees on the left are noticeably lower in elevation

Recognizing this microclimate is important to my gardening and plant selection. And I've made mistakes by not analyzing it earlier. Initially I planted Irises under the trees in the lower stand. They get full sun in early spring before the trees leaf out and I thought that would be enough for their success. The problem comes in autumn. As you might guess, the upper Aspen stands drop their leaves first and this lower stand is the last to lose leaves in fall. That means that the Irises are still shaded when they should be getting sun to nourish their rhizomes. I never get the flowers I should because the Iris rhizomes aren't nourished by sunlight as well as they should be.

This microclimate analysis changed my approach to plant selection. First, I planted new lavender plants near the upper Aspen stand. The slightly improved sun exposure helped those lavender plants grow better than others in the back yard. This year I've planted Coral Bells (Heuchera) in that lower spot. Coral Bells like sun when it's cold and some shade when it's hot, exactly what the location offers.

Without a microclimate analysis I might spend years fertilizing and babying the Irises and other plants that were never really suited for that garden bed. Now I can focus on the proper plants for better success.

Another microclimate, that I created, is evident in my stone patio. I wanted a spot to support the growing requirements of lavender and other high desert plants. I chose a location that gets full sun and build a raised, stone patio. It is now the spot that warms quickly in spring and where snow melts first. The lavender, sedum, thyme, and iceplants are thriving in a spot designed for them.

The warmer stone helps nearby plants in early spring

I chose a nice location with full sun for my vegetable garden. But even in this select area microclimates exist. The raised beds are built on a slope and the upper beds are a few feet higher in elevation than the lower. The upper beds have more exposure to wind and receive late-day shade before the others. Last year tomato plants in the lower beds did better than tomato plants just a few feet away; the wind and shade made a difference even though it is barely noticeable to me. The plants obviously noticed.

A slope with trees can create many microclimates

Look at how your garden wakes up in spring. Note the different growth rates of plants just a few feet apart. Spot elevation, sun, and wind variations in your landscape. Take a few minutes to analyze why some plants do well while others struggle.

By thinking about microclimates in your garden and acting to match plants with the best growing environment you can improve your garden's success. We often don't think much about a minor difference in temperature, sun, or shade, but to tender plants it can mean the difference between life and death.

Before you put new plants in a garden bed and before you sow seeds notice the year-round characteristics of that spot of ground. It may be perfect for young plants in the spring but does it offer the best environment and microclimate later in the plant's life cycle? The best gardening practices look into the future. It may sound difficult but it begins by thinking about how little differences in localized climate exists from one section of your garden to another. By spotting these changes you can use microclimates to your advantage.

Link to:

"Look for Microclimates in the Garden"
"Microclimates in Summer"

When the Last Frost Date Isn't the Last Frost Date

The United States abounds with record high temperatures this month and spring arrived early in many places. I've been enjoying days that are 15 and even 20 degrees above normal for weeks; unusual is an understatement. At a time of year we normally cringe at the thought of more, freezing overnight temperatures, sunscreen and shade are now on my mind. This is a year when the projected official last frost date won't even be close. Maybe.

Late spring frost on apricot flowers

The last frost date for me is still more than two weeks away. That is, the official 90% last frost date is the 15th of May for my area. My garden is at a higher elevation than the city proper so I always add a few days to be safe, but it's close. As I've written before (Mar 18, 2011, "Know Your Last Frost Date"; Mar 29, 2011, "What to Plant Before the Last Frost"; May 13, 2011, "What is the Last Frost Date?"), the "90% last frost date" is the one most often referred to by seed companies, the USDA, NOAA, and anyone else that throws out a date as the last one for gardeners to be concerned about.

Last year I got my last frost on May 15; the model proved true. This year the actual last frost in my garden should be different. In fact, I think the last frost happened yesterday.

Last year's snow in May

Last Frost Dates are determined by taking historical temperature data and finding a symbolic date that meets certain criteria. The "90% last frost date" is the date for a certain area when 90 percent of historical last frosts have already occurred. The "Average Last Frost Date" or "50% last frost date" is the point on the calendar when half of the historical last frosts have already happened. The third type of last frost date is the "10% last frost date"; by this date 10 percent of historical last frosts were final. The key to all of these dates is that they're determined by using historical dates, days that occurred in the past.

For my garden zone, 10 percent of the last frost dates in years past happened by April 24, and 50 percent happened by May 4. Could this be another one of those kind of years?

As far back as I can remember, in my 15 years living here, the last frost happened in May. I always advise local gardeners to wait until late May to plant warm season plants. Many gardeners new to the area learn the hard way about planting too soon in our high-mountain, weather-crazy area.

This year is one of the ones that cause serious gardeners like me to start biting our nails and tearing out our hair. A look at the long-range weather forecast shows we'll be well above freezing for the next 10 days. That puts us very close to the 90% last frost date with no worries. Historically, we can point to previous years like this one when no frost occurred in May.

Then again I can point to years when we had frosts in June. A month is a long time in the weather world. Something could be brewing off the coast of northern Alaska right now that won't be revealed until two or three weeks from now. A blast of Arctic air might descend on my garden when I least expect it. Or not.

The last frost date is just a spot on the calendar for garden planning. It's up to individual gardeners to determine what they do with it. With any mathematical model, some points of data lie well outside the norm. For a date to be considered average (technically the mean), half of statistical points happened before and half happened after. It's nice that we gardeners have the 90% and 10% last frost dates at our disposal to develop a more precise planting plan.

As I look at my calendar, every day without frost puts me closer to the mathematical point when future frost isn't likely to happen. I've passed the 10 percent point and should breeze past the 50 percent point with no problem. The 90 percent point looks very promising.

Does that mean I can relax and plant with no frost concerns? That's a good question and one for which I wish I had the answer. Whatever I choose to do I have to be ready for the consequences... or rewards. Knowing how last frost dates are determined and using that knowledge will help me make an informed decision when it comes to planting.

I've just about convinced myself that this is one of those years when the last frost occurs early. Indications are good that warm days and nights ahead will help my plants. The ground is already warmer than it normally is at this point of the year. The weather trends seem positive.

But I'm not a gambler and I'm not ready to bet everything on a statistical probability. I'll plant tomatoes next week almost a month ahead of normal, but I'll enclose them in plastic season extenders. I'll put some beans in the ground, but only in the beds with protective covering. I'll delay planting squash and pumpkins until I'm absolutely sure the calendar coast is clear.

Usually I wouldn't be considering such measures at the end of April, but this year is different. Sunny days are too inviting to sit back and wait for historical events to happen. Part of being a gardener is trying new things in the garden and by a small measure I'll roll the dice a little. We all experience missteps and minor failures in gardening so I'm ready for the worst, but if my conjecture about the last frost date holds true I'll be able to get a nice jump on the growing season.

I know my last frost date, all three of them actually. I know what they mean. I have experienced the ups and downs of weather's effect on my garden. Also I'm anxious to get my garden growing. This year my last frost date won't be an actual last frost date. That's what I've determined based on the data at hand. Or at least that's what I'm betting on.

The United States abounds with record high temperatures this month and spring arrived early in many places. I've been enjoying days that are 15 and even 20 degrees above normal for weeks; unusual is an understatement. At a time of year we normally cringe at the thought of more, freezing overnight temperatures, sunscreen and shade are now on my mind. This is a year when the projected official last frost date won't even be close. Maybe.

Late spring frost on apricot flowers

The last frost date for me is still more than two weeks away. That is, the official 90% last frost date is the 15th of May for my area. My garden is at a higher elevation than the city proper so I always add a few days to be safe, but it's close. As I've written before (Mar 18, 2011, "Know Your Last Frost Date"; Mar 29, 2011, "What to Plant Before the Last Frost"; May 13, 2011, "What is the Last Frost Date?"), the "90% last frost date" is the one most often referred to by seed companies, the USDA, NOAA, and anyone else that throws out a date as the last one for gardeners to be concerned about.

Last year I got my last frost on May 15; the model proved true. This year the actual last frost in my garden should be different. In fact, I think the last frost happened yesterday.

Last year's snow in May

Last Frost Dates are determined by taking historical temperature data and finding a symbolic date that meets certain criteria. The "90% last frost date" is the date for a certain area when 90 percent of historical last frosts have already occurred. The "Average Last Frost Date" or "50% last frost date" is the point on the calendar when half of the historical last frosts have already happened. The third type of last frost date is the "10% last frost date"; by this date 10 percent of historical last frosts were final. The key to all of these dates is that they're determined by using historical dates, days that occurred in the past.

For my garden zone, 10 percent of the last frost dates in years past happened by April 24, and 50 percent happened by May 4. Could this be another one of those kind of years?

As far back as I can remember, in my 15 years living here, the last frost happened in May. I always advise local gardeners to wait until late May to plant warm season plants. Many gardeners new to the area learn the hard way about planting too soon in our high-mountain, weather-crazy area.

This year is one of the ones that cause serious gardeners like me to start biting our nails and tearing out our hair. A look at the long-range weather forecast shows we'll be well above freezing for the next 10 days. That puts us very close to the 90% last frost date with no worries. Historically, we can point to previous years like this one when no frost occurred in May.

Then again I can point to years when we had frosts in June. A month is a long time in the weather world. Something could be brewing off the coast of northern Alaska right now that won't be revealed until two or three weeks from now. A blast of Arctic air might descend on my garden when I least expect it. Or not.

The last frost date is just a spot on the calendar for garden planning. It's up to individual gardeners to determine what they do with it. With any mathematical model, some points of data lie well outside the norm. For a date to be considered average (technically the mean), half of statistical points happened before and half happened after. It's nice that we gardeners have the 90% and 10% last frost dates at our disposal to develop a more precise planting plan.

As I look at my calendar, every day without frost puts me closer to the mathematical point when future frost isn't likely to happen. I've passed the 10 percent point and should breeze past the 50 percent point with no problem. The 90 percent point looks very promising.

Does that mean I can relax and plant with no frost concerns? That's a good question and one for which I wish I had the answer. Whatever I choose to do I have to be ready for the consequences... or rewards. Knowing how last frost dates are determined and using that knowledge will help me make an informed decision when it comes to planting.

I've just about convinced myself that this is one of those years when the last frost occurs early. Indications are good that warm days and nights ahead will help my plants. The ground is already warmer than it normally is at this point of the year. The weather trends seem positive.

But I'm not a gambler and I'm not ready to bet everything on a statistical probability. I'll plant tomatoes next week almost a month ahead of normal, but I'll enclose them in plastic season extenders. I'll put some beans in the ground, but only in the beds with protective covering. I'll delay planting squash and pumpkins until I'm absolutely sure the calendar coast is clear.

Usually I wouldn't be considering such measures at the end of April, but this year is different. Sunny days are too inviting to sit back and wait for historical events to happen. Part of being a gardener is trying new things in the garden and by a small measure I'll roll the dice a little. We all experience missteps and minor failures in gardening so I'm ready for the worst, but if my conjecture about the last frost date holds true I'll be able to get a nice jump on the growing season.

I know my last frost date, all three of them actually. I know what they mean. I have experienced the ups and downs of weather's effect on my garden. Also I'm anxious to get my garden growing. This year my last frost date won't be an actual last frost date. That's what I've determined based on the data at hand. Or at least that's what I'm betting on.

Extreme Temperature Changes and Gardening

Did you ever plan a vacation to Florida and get off the plane in North Dakota? Would you want to? I once left Hawaii where it was 82F degrees (28C) and sunny and landed hours later in Montana where it was -10F (-23C) degrees and snowing. It's an experience I don't recommend repeating.

Late winter often provides some of us similar extremes and we don't have to leave home to experience them. Residents along the Front Range of the Rocky Mountains are in the middle of such an event and much of the Eastern U.S. will follow soon.

Yesterday we enjoyed a high temperature near 70F degrees (21C). Today will be about 45F (7C) and tomorrow we'll be lucky to reach 30F (-1C) for a daily high. The low temperature tonight will reach 10F (-12C). Along with an 80-degree temperature difference in just over a day, we'll also receive inches of snow.

I knew about the forecast temperature in Montana when I left Hawaii and was able to put warm clothes on in the airplane. I can do the same tonight and tomorrow for this storm. But my plants are like the vacationers to Florida. They're prepared for sunny, warm weather and are about to be surprised by an unexpected arrival in Minot, North Dakota.

This bird was caught in a sudden spring storm

This is the time of year that can lead to damage and death of many garden plants. During the gradual climate changes of fall and early winter, plants prepare for cold conditions and change their growth cycles accordingly. In late winter and early spring as weather and soil warms, many plants come back to life and begin growing again. When a sudden burst of arctic cold interrupts that cycle they can suffer.

As a concerned and conscientious gardener it's my job to try to reduce that suffering. By taking a few simple precautions I can limit plant damage when faced with a huge temperature swing.

It's important to note that not all plants need protecting when conditions like these threaten. I encourage gardeners to make a regular survey of their gardens. That's why I'm often wandering through the garden at this time of year to check on plant growth. Many sections of my yard are still buried in snow and have no new growth. Some shaded spots still have frozen ground. It's only the areas that have started to thaw and where the plants have responded that need attention.

And even in those areas not every plant is a concern. There are perennial plants like some of my daisies and penstemons that shrug off the cold. The strawberries are peeking above the mulch but can handle freezing conditions. Many groundcovers don't care how cold they get. A lot of plants stay partially green even through cold winters and are ready to grow rapidly when spring finally arrives. A sudden 80-degree temperature shift may slow them down but it won't kill them. I'm not worried about those plants.

Snow and cold don't affect the daisies

It's the bushes and small trees that concern me most. Buds begin to open and grow on the warm days
and they're not designed to handle extreme cold. If they grow too soon in the season and get hit by harsh cold, damaged buds affect branch, flower, and fruit growth. I've had an entire apricot tree lose its blossoms in an April snow.

Frozen blossoms

A tarp or blanket thrown over the plant can head off disaster. By shielding the plant and holding in some of the heat from the warm day, a simple covering can prevent serious damage. You may not be able to protect the entire bush or tree, but anything saved is good. You can't cover larger bushes and trees and they will probably lose buds in severe temperature changes, but their size and girth should provide some natural protection.

Small and young perennial plants are most susceptible. I lost 10 lavender plants about this time last year. They were planted in early fall and made it through the winter fine. I kept them covered with protective straw through the worst months. A fellow master gardener and I checked their new growth after early-season, warm weather and confirmed they were alive, supple, and doing well. A devastating cold surge a week later changed all that.

A frozen, young lavender

Simple milk jug coverings can cover and save small plants. The protective umbrella holds some of the soil and plant heat in, usually enough to counter the sudden cold. If they're sturdy or if you provide short supports, a tarp thrown over a grouping of plants can save them all. The concept is just to give them some protection from the cold.

Plastic covers help young growth

A close look at the forecast can save you some effort and worry. Snow is a great insulator and actually provides protection. Snow does not get much colder than 32F degrees (0C). That's warmer than our current average night temperatures so any buds that are growing can handle 32 degrees. A blanket of snow provides a relatively constant temperature that can be well above the extreme low temperature of outside air.

So that means that if the forecast calls for inches of snow before the severe cold temperatures, a natural blanket will help the plants and less covering may be needed. If the forecast has the cold temperatures coming before the snow, that's when you have to take protective action.

By focusing on plants you know are growing and that you know are susceptible to cold damage you can center your protective efforts. By analyzing the type of weather expected you can decide how much action is necessary.

In the end, how many of your plants survive drastic and severe temperature changes may be up to you. I'll take another look this afternoon before temperatures plummet to make a final evaluation. My tarps and milk jugs are ready.

Did you ever plan a vacation to Florida and get off the plane in North Dakota? Would you want to? I once left Hawaii where it was 82F degrees (28C) and sunny and landed hours later in Montana where it was -10F (-23C) degrees and snowing. It's an experience I don't recommend repeating.

Late winter often provides some of us similar extremes and we don't have to leave home to experience them. Residents along the Front Range of the Rocky Mountains are in the middle of such an event and much of the Eastern U.S. will follow soon.

Yesterday we enjoyed a high temperature near 70F degrees (21C). Today will be about 45F (7C) and tomorrow we'll be lucky to reach 30F (-1C) for a daily high. The low temperature tonight will reach 10F (-12C). Along with an 80-degree temperature difference in just over a day, we'll also receive inches of snow.

I knew about the forecast temperature in Montana when I left Hawaii and was able to put warm clothes on in the airplane. I can do the same tonight and tomorrow for this storm. But my plants are like the vacationers to Florida. They're prepared for sunny, warm weather and are about to be surprised by an unexpected arrival in Minot, North Dakota.

This bird was caught in a sudden spring storm

This is the time of year that can lead to damage and death of many garden plants. During the gradual climate changes of fall and early winter, plants prepare for cold conditions and change their growth cycles accordingly. In late winter and early spring as weather and soil warms, many plants come back to life and begin growing again. When a sudden burst of arctic cold interrupts that cycle they can suffer.

As a concerned and conscientious gardener it's my job to try to reduce that suffering. By taking a few simple precautions I can limit plant damage when faced with a huge temperature swing.

It's important to note that not all plants need protecting when conditions like these threaten. I encourage gardeners to make a regular survey of their gardens. That's why I'm often wandering through the garden at this time of year to check on plant growth. Many sections of my yard are still buried in snow and have no new growth. Some shaded spots still have frozen ground. It's only the areas that have started to thaw and where the plants have responded that need attention.

And even in those areas not every plant is a concern. There are perennial plants like some of my daisies and penstemons that shrug off the cold. The strawberries are peeking above the mulch but can handle freezing conditions. Many groundcovers don't care how cold they get. A lot of plants stay partially green even through cold winters and are ready to grow rapidly when spring finally arrives. A sudden 80-degree temperature shift may slow them down but it won't kill them. I'm not worried about those plants.

Snow and cold don't affect the daisies

It's the bushes and small trees that concern me most. Buds begin to open and grow on the warm days
and they're not designed to handle extreme cold. If they grow too soon in the season and get hit by harsh cold, damaged buds affect branch, flower, and fruit growth. I've had an entire apricot tree lose its blossoms in an April snow.

Frozen blossoms

A tarp or blanket thrown over the plant can head off disaster. By shielding the plant and holding in some of the heat from the warm day, a simple covering can prevent serious damage. You may not be able to protect the entire bush or tree, but anything saved is good. You can't cover larger bushes and trees and they will probably lose buds in severe temperature changes, but their size and girth should provide some natural protection.

Small and young perennial plants are most susceptible. I lost 10 lavender plants about this time last year. They were planted in early fall and made it through the winter fine. I kept them covered with protective straw through the worst months. A fellow master gardener and I checked their new growth after early-season, warm weather and confirmed they were alive, supple, and doing well. A devastating cold surge a week later changed all that.

A frozen, young lavender

Simple milk jug coverings can cover and save small plants. The protective umbrella holds some of the soil and plant heat in, usually enough to counter the sudden cold. If they're sturdy or if you provide short supports, a tarp thrown over a grouping of plants can save them all. The concept is just to give them some protection from the cold.

Plastic covers help young growth

A close look at the forecast can save you some effort and worry. Snow is a great insulator and actually provides protection. Snow does not get much colder than 32F degrees (0C). That's warmer than our current average night temperatures so any buds that are growing can handle 32 degrees. A blanket of snow provides a relatively constant temperature that can be well above the extreme low temperature of outside air.

So that means that if the forecast calls for inches of snow before the severe cold temperatures, a natural blanket will help the plants and less covering may be needed. If the forecast has the cold temperatures coming before the snow, that's when you have to take protective action.

By focusing on plants you know are growing and that you know are susceptible to cold damage you can center your protective efforts. By analyzing the type of weather expected you can decide how much action is necessary.

In the end, how many of your plants survive drastic and severe temperature changes may be up to you. I'll take another look this afternoon before temperatures plummet to make a final evaluation. My tarps and milk jugs are ready.

Changes to the USDA Plant Hardiness Zone Map

Yesterday, the U.S. Department of Agriculture released a new version of the Plant Hardiness Zone Map. This is the first revision of the map since 1990. The new version includes 13 zones, two more than before. Much of the United States is now one half-zone warmer.

The old map

The new map reflects an increase in the average temperature of the U.S. in recent decades. The 1990 map used average annual temperatures from 1974 to 1986 while the new map uses information from 1976 to 2005.

For the first time, the influence of factors like elevation, prevailing winds, large bodies of water, terrain, and city heat island effects are included in calculations. I've written previously about how these aspects can affect specific regions, cities, and gardens. New algorithms and more sophisticated mapping methods now account for those effects. The Associated Press points out that American cities that include St. Louis, Des Moines, Honolulu, and Fairbanks, Alaska, are now in warmer Plant Hardiness Zones.

The map changes mean that, generally, the coldest winter day isn't as cold as in the past. Relatively mild winters of the last two decades now allow some plants to grow in areas previously considered off limits.

You can expect that seed packets and gardening advisers will soon change and use the new data for recommending what plants can grow where. Burpee will include the new map on next year's seed packets. Gardening catalogs will identify which plants are suitable for the warmer zones.

It's important that I point out that the Plant Hardiness Map should only be used as a guide for planting.

Climate can still vary dramatically within zones, even the new ones. While some mountain areas are now in a cooler zone, a review of the new zone map still has my neighborhood in the same zone as before, 5b.  This doesn't adequately account for the terrain and altitude differences that my neighbors and I encounter. My garden is fully 1,000 feet higher than the city 15 miles away, also zone 5b. I'm surrounded by forest. I have inches of snow and ice still on the ground from our first major winter storm well over a month ago; the city lost its snow covering the first day after the storm.

Every gardener should learn about the individual characteristics of their region and garden. Knowing your Plant Hardiness Zone is important. It will help you choose seeds and plants, but it is only one part of gardening planning.

Get to know your garden. Just because the USDA says you're in a new zone it doesn't mean everything has changed. The Hardiness Zone Map is based on averages, average low temperatures. The averages may be warmer, but extreme low temperatures can still be possible. Caution should still be practiced when choosing plants that are barely suitable for your zone, old or new.

The new map is more accurate than previous versions and gardeners have a new tool as we confront climate change. Like the rest of our gardening tools it is appropriate only for its intended purpose.

If you haven't had success with a particular plant, a new zone number probably won't change that. If you want to seek out new plants a new zone number may give you new options, but it is only a guideline.

I accept the new map with anticipation. Many gardeners in many places will try new things and that is a great idea. Entire regions are more accurately assessed. Yet even though most of us feel like our neighborhood is warmer, experience is a harsh steward. I'll continue to recommend that gardeners, particularly in challenging zones like mine, choose plants that are best suited for success.

It only takes one or two days of historical low temperatures to wipe out plantings that should expect to survive the new zone identifications. If you live in an area of surprise temperature extremes, it's better to opt for plants a zone lower than yours -- planting 4b plants when you live in 5b -- than trying to recover from winter kill.

Of course, microclimates, cold frames, hoop houses, and other season extenders will all provide the extra protection that you may need for plants challenged by temperature. If you're going to try new plants that may be questionable consider one of these aids. Check out some of my other articles on those subjects for more assistance.

For now enjoy better information and access. The new USDA Plant Hardiness Zone Map has an improved online interface. Easier than in the past, you only need to enter your zip code for an instant zone report. A click of your mouse will bring up your color-coded state map.

Try it at:

http://planthardiness.ars.usda.gov/PHZMWeb/

  

Yesterday, the U.S. Department of Agriculture released a new version of the Plant Hardiness Zone Map. This is the first revision of the map since 1990. The new version includes 13 zones, two more than before. Much of the United States is now one half-zone warmer.

The old map

The new map reflects an increase in the average temperature of the U.S. in recent decades. The 1990 map used average annual temperatures from 1974 to 1986 while the new map uses information from 1976 to 2005.

For the first time, the influence of factors like elevation, prevailing winds, large bodies of water, terrain, and city heat island effects are included in calculations. I've written previously about how these aspects can affect specific regions, cities, and gardens. New algorithms and more sophisticated mapping methods now account for those effects. The Associated Press points out that American cities that include St. Louis, Des Moines, Honolulu, and Fairbanks, Alaska, are now in warmer Plant Hardiness Zones.

The map changes mean that, generally, the coldest winter day isn't as cold as in the past. Relatively mild winters of the last two decades now allow some plants to grow in areas previously considered off limits.

You can expect that seed packets and gardening advisers will soon change and use the new data for recommending what plants can grow where. Burpee will include the new map on next year's seed packets. Gardening catalogs will identify which plants are suitable for the warmer zones.

It's important that I point out that the Plant Hardiness Map should only be used as a guide for planting.

Climate can still vary dramatically within zones, even the new ones. While some mountain areas are now in a cooler zone, a review of the new zone map still has my neighborhood in the same zone as before, 5b.  This doesn't adequately account for the terrain and altitude differences that my neighbors and I encounter. My garden is fully 1,000 feet higher than the city 15 miles away, also zone 5b. I'm surrounded by forest. I have inches of snow and ice still on the ground from our first major winter storm well over a month ago; the city lost its snow covering the first day after the storm.

Every gardener should learn about the individual characteristics of their region and garden. Knowing your Plant Hardiness Zone is important. It will help you choose seeds and plants, but it is only one part of gardening planning.

Get to know your garden. Just because the USDA says you're in a new zone it doesn't mean everything has changed. The Hardiness Zone Map is based on averages, average low temperatures. The averages may be warmer, but extreme low temperatures can still be possible. Caution should still be practiced when choosing plants that are barely suitable for your zone, old or new.

The new map is more accurate than previous versions and gardeners have a new tool as we confront climate change. Like the rest of our gardening tools it is appropriate only for its intended purpose.

If you haven't had success with a particular plant, a new zone number probably won't change that. If you want to seek out new plants a new zone number may give you new options, but it is only a guideline.

I accept the new map with anticipation. Many gardeners in many places will try new things and that is a great idea. Entire regions are more accurately assessed. Yet even though most of us feel like our neighborhood is warmer, experience is a harsh steward. I'll continue to recommend that gardeners, particularly in challenging zones like mine, choose plants that are best suited for success.

It only takes one or two days of historical low temperatures to wipe out plantings that should expect to survive the new zone identifications. If you live in an area of surprise temperature extremes, it's better to opt for plants a zone lower than yours -- planting 4b plants when you live in 5b -- than trying to recover from winter kill.

Of course, microclimates, cold frames, hoop houses, and other season extenders will all provide the extra protection that you may need for plants challenged by temperature. If you're going to try new plants that may be questionable consider one of these aids. Check out some of my other articles on those subjects for more assistance.

For now enjoy better information and access. The new USDA Plant Hardiness Zone Map has an improved online interface. Easier than in the past, you only need to enter your zip code for an instant zone report. A click of your mouse will bring up your color-coded state map.

Try it at:

http://planthardiness.ars.usda.gov/PHZMWeb/

  

Unexpected Plant Damage in Winter

It's tough being a plant during crazy weather patterns. Almost every location on the planet seems to be experiencing abnormal temperature variations while people and animals are left wondering what's going on. Even the Amundsen-Scott South Pole Station recently set an all-time high temperature reading of 9.9F degrees (-12.27C). As confused as humans get when we try to decide if we should grab a sweater or jacket or just brave the day in shirtsleeves, plants have no way to make similar decisions when confronting the same situations.

Most perennial plants and trees and shrubs are genetically wired to respond to warming temperatures. When a trend of ever-increasing daily temperatures is registered, it usually means that spring has arrived. That means it's time to wake up, time to open up the sleeping buds, time to sprout forth green growth. Plants react to the changes with no reference to a calendar.

When the warming trend is a fluke, the plant can suffer. Recently I enjoyed a week-long period of temperatures more than 20F degrees above average. December should give me days in the 40s (4C). Instead I enjoyed days in the 60s (16C). This winter has been relatively mild and many sections of my lawn are still green, even under the snow. With this trend of unusual warmth it's important to remember the rest of my landscape.


While it's not unusual for some non-evergreen perennial plants to have evergreen parts, my daisies have kept more green leaves at their core than I remember in recent years. They're ready to grow.

My daisies don't know it's not spring

Many of my herbs are still alive with some new green at the base of my thyme and mint.

When I take a close look at my young fruit trees, it appears that some of the buds are beginning to swell, a sign that maybe they are receiving extra energy from the tree in anticipation of leaf growth. On some of the branches some buds already sprouted little leaves. The tree is confused, "thinking" that spring has arrived.

Early-winter apple tree growth can't be sustained

It's usually a great sign when new growth appears. We herald the return of spring. But for me it's early January, the heart of winter. While yesterday was another warm day, this morning welcomed us with blowing snow and a high that will be 20 degrees colder, and below freezing.

We can put on another layer of clothes and a warmer jacket. Plants have no such recourse. The tiny hope of new leaves on my apple tree will succumb to the cold. If not tonight when the low temperature is expected to drop near 0F (-18C), then soon when the lows will probably sink lower than that.

Daisy leaves can handle temperatures well below freezing, but if they're is exposed to historical lows in my area that can still hit -30F (-34C), they'll suffer.

Freezing temperatures below what a plant is designed to handle will kill new growth. The Daisy leaves won't survive to provide life-sustaining nutrients when the plant is ready to send up flower stalks. My herbs will shrivel. The awakened apple tree buds won't grow into strong new branches or tasty fruit.

The entire plant may not be killed in these conditions, but it can be damaged. Bushes and shrubs won't produce as many branches or flowers. Trees may lose the important buds that control their central trunk growth, resulting in new branch forks and ultimately reduced strength. Perennials can be stunted with less foliage and fewer flowers during the prime growing season. Fruit canes and trees may not bear at all.

There are a few things you can do if you're encountering the same conditions as I. Just as we appreciate a warm coat on a cold night, some plants can be saved by giving them a blanket. If you have new growth on a low-lying plant and are expecting frigid weather, cover it with a wool blanket or a tarp during the day before the low temperatures hit; you may be able to trap enough heat to give it a fighting chance. Surround and cover plants with a thick layer of straw. If you're lucky enough to have snow, leave it in place around your plants. Snow will keep the temperature near the freezing point, but that may be well above the colder air temperatures that can kill new growth.

A cover of hay should be enough to protect new lavender

For trees and larger plants that can't be covered, expect repercussions from excessive warm-cold weather cycles. Don't be surprised when there are fewer leaves to produce shade or fewer new branches for height and depth. When a new side branch appears in a few years that redirects the primary growth pattern, remember this year.

Much of the time all we can do is react to the harsh reality of drastic temperature swings. Severe pruning may be necessary to eliminate dead branches. Entire plants may die and need to be replaced. Low crop yield shouldn't be a surprise.

It's difficult watching the inevitable decline, damage, or death of a plant. I wonder what effect today's cold will have on tomorrow's growth. Having no control over the situation is uncomfortable for a gardener.

All gardener's in cold regions have and will experience this problem, probably more-so in the future. Knowing that others are going through the same dilemma may be slightly helpful, but certainly not comforting.

It's tough being a plant during crazy weather patterns. Almost every location on the planet seems to be experiencing abnormal temperature variations while people and animals are left wondering what's going on. Even the Amundsen-Scott South Pole Station recently set an all-time high temperature reading of 9.9F degrees (-12.27C). As confused as humans get when we try to decide if we should grab a sweater or jacket or just brave the day in shirtsleeves, plants have no way to make similar decisions when confronting the same situations.

Most perennial plants and trees and shrubs are genetically wired to respond to warming temperatures. When a trend of ever-increasing daily temperatures is registered, it usually means that spring has arrived. That means it's time to wake up, time to open up the sleeping buds, time to sprout forth green growth. Plants react to the changes with no reference to a calendar.

When the warming trend is a fluke, the plant can suffer. Recently I enjoyed a week-long period of temperatures more than 20F degrees above average. December should give me days in the 40s (4C). Instead I enjoyed days in the 60s (16C). This winter has been relatively mild and many sections of my lawn are still green, even under the snow. With this trend of unusual warmth it's important to remember the rest of my landscape.


While it's not unusual for some non-evergreen perennial plants to have evergreen parts, my daisies have kept more green leaves at their core than I remember in recent years. They're ready to grow.

My daisies don't know it's not spring

Many of my herbs are still alive with some new green at the base of my thyme and mint.

When I take a close look at my young fruit trees, it appears that some of the buds are beginning to swell, a sign that maybe they are receiving extra energy from the tree in anticipation of leaf growth. On some of the branches some buds already sprouted little leaves. The tree is confused, "thinking" that spring has arrived.

Early-winter apple tree growth can't be sustained

It's usually a great sign when new growth appears. We herald the return of spring. But for me it's early January, the heart of winter. While yesterday was another warm day, this morning welcomed us with blowing snow and a high that will be 20 degrees colder, and below freezing.

We can put on another layer of clothes and a warmer jacket. Plants have no such recourse. The tiny hope of new leaves on my apple tree will succumb to the cold. If not tonight when the low temperature is expected to drop near 0F (-18C), then soon when the lows will probably sink lower than that.

Daisy leaves can handle temperatures well below freezing, but if they're is exposed to historical lows in my area that can still hit -30F (-34C), they'll suffer.

Freezing temperatures below what a plant is designed to handle will kill new growth. The Daisy leaves won't survive to provide life-sustaining nutrients when the plant is ready to send up flower stalks. My herbs will shrivel. The awakened apple tree buds won't grow into strong new branches or tasty fruit.

The entire plant may not be killed in these conditions, but it can be damaged. Bushes and shrubs won't produce as many branches or flowers. Trees may lose the important buds that control their central trunk growth, resulting in new branch forks and ultimately reduced strength. Perennials can be stunted with less foliage and fewer flowers during the prime growing season. Fruit canes and trees may not bear at all.

There are a few things you can do if you're encountering the same conditions as I. Just as we appreciate a warm coat on a cold night, some plants can be saved by giving them a blanket. If you have new growth on a low-lying plant and are expecting frigid weather, cover it with a wool blanket or a tarp during the day before the low temperatures hit; you may be able to trap enough heat to give it a fighting chance. Surround and cover plants with a thick layer of straw. If you're lucky enough to have snow, leave it in place around your plants. Snow will keep the temperature near the freezing point, but that may be well above the colder air temperatures that can kill new growth.

A cover of hay should be enough to protect new lavender

For trees and larger plants that can't be covered, expect repercussions from excessive warm-cold weather cycles. Don't be surprised when there are fewer leaves to produce shade or fewer new branches for height and depth. When a new side branch appears in a few years that redirects the primary growth pattern, remember this year.

Much of the time all we can do is react to the harsh reality of drastic temperature swings. Severe pruning may be necessary to eliminate dead branches. Entire plants may die and need to be replaced. Low crop yield shouldn't be a surprise.

It's difficult watching the inevitable decline, damage, or death of a plant. I wonder what effect today's cold will have on tomorrow's growth. Having no control over the situation is uncomfortable for a gardener.

All gardener's in cold regions have and will experience this problem, probably more-so in the future. Knowing that others are going through the same dilemma may be slightly helpful, but certainly not comforting.

Gardening for Winter Interest

Gardening can be a four-season activity. We all know about the new colors and verdant growth of spring, the abundance of life in summer, and the waning harvests of fall, but winter is often disregarded as an important gardening season. I love my winter landscape and the season provides wonderful opportunities for unique garden appreciation. It begins by choosing to garden for winter interest.

Coneflowers lose little appeal in winter

You garden for winter interest expecting and looking forward to the days of cold. It's not much different than planning your plantings to enjoy the color and texture and size of varied plants during their prime growing time. By gardening for winter interest you imagine how the same plants will look when covered with frost or ice or snow. You anticipate how they will appear when dead or dormant.

On cloudy, gloomy days the brown and plain foliage of dead flowers, grasses, and shrubs can be quite dreary. I'll grant you that. The same can be said of new, plain growth during dark, rainy days in spring. But just as the returning sun creates a vibrant display of color and excitement when it glistens on the dew and raindrops nestling on the young plants, the remnants of a winter storm can transform the garden into a brilliant, magical wonderland.

Sun-loving Heliopsis covered in crystals

When the wonderful combination of frigid temperatures and moist air combine appropriately, a cold night meets a sunny morning with ice crystals covering the landscape. The dreary brown plants are transformed into shimmering, diamond encrusted works of natural art. This is when the garden offers beauty that competes dramatically with the highlights of summer.

Gardening for winter interest has a few basic steps. First is the selection of appropriate plants.  Some plants that provide a strong presence in a spring or summer garden, like Hostas, Lilies, and Irises, have their flowers and leaves wither away with the cold temperatures of fall; there is little left of them in winter. Selecting plants whose physical structure can stand up to strong winds, freezing weather, and heavy snow allows the winter garden to exist. At this point I'm not talking about plants that can survive and live in the cold, but about plants with sturdy stalks, and flowers, and branches after the green life has faded. Plants that offer height above the blanket of snow and ice are better than low plantings that will be covered and unappreciated.

Sunflowers bloom with icy flowers

In my garden, sunflowers, coneflowers, Yarrow, Heliopsis, and Kniphofia offer great scaffolds for the natural ice and snow sculptures of winter. Ornamental grasses and shrubs and bushes anchor the garden when snow falls.

Some plants like Red Twig Dogwood and Burning Bush are at their best in winter as they display dynamic reds against the white snow. Plants with yellow, red, and purple branches are readily available to add a rainbow of color that is often missing in a typical gardener's winter yard once green leaves have disappeared.


Of course plant selection for winter interest does include life; you can think beyond the death of plants and how they look in that state. Ornamental Kale can survive harsh conditions in many regions and displays beautiful greens and purples and reds even when covered in ice. Witch Hazel is a large shrub that flowers in winter. Holly with its evergreen leaves and berries welcomes Christmas with green and red. The parasitic evergreen plant Mistletoe achieved its mythical powers because of its colorful winter state. Mountain Laurels and Yews are evergreens many gardeners overlook in their landscape. There are many colorful winter plants available for your garden.

The second in gardening for winter interest is to leave your plants in place through the cold months. Many gardeners are anxious to clean up their beds as soon as the first freeze fades the foliage. They hack at and pull up the dead, dying, and dormant plants and cart them away. They rake fallen leaves into bags and leave the garden barren, ready for spring planting.  There is nothing wrong with gardening this way, but when old man winter arrives with his brush and palette there is no canvas to receive the artwork.

Ornamental grass shimmering in the winter sun

Besides giving birds and wildlife food and cover in winter, leaving your plants in place will add visual variety to your landscape. The textures and shapes of bare plants after their leaves are gone can only be appreciated during the shortest days of the year. There will be time to clean up the garden in spring when the winter appeal wanes.

Delaying pruning is easy to do. Leave excess branches on trees in early winter. Don't cut the stalks of perennial flowers. The erratic and ungainly growth of flower and shrubs pose nicely in frigid weather.

Simply selecting plants based on how they will look in winter and then leaving them to compose their own beauty is all that is needed to create a garden with winter interest.

To begin next year's winter garden look at your landscape and those of your friends and neighbors. Do you have a spot that is glaringly bare and lifeless in winter? Do you see something that stands out as brilliant in another's landscape? Tour a local botanical garden for ideas. Take the time to observe plants in winter. Think beyond the color and life of summer.

Even my garden art glistens after a frost

During the dark days of winter cold, gardeners often fail to see their garden's beauty, focused on how it will look when the flowers return. While I fall into this pattern too, it only takes an ice storm or cold morning fog to awaken a sense of wonderment. Traipsing through the snow, hearing the sharp crunch of ice, I peer into the world of Jack Frost. It's amazing how a garden can feel so alive when so little is actually growing. It's all about the icy visuals and sustaining your garden for winter interest.

Gardening can be a four-season activity. We all know about the new colors and verdant growth of spring, the abundance of life in summer, and the waning harvests of fall, but winter is often disregarded as an important gardening season. I love my winter landscape and the season provides wonderful opportunities for unique garden appreciation. It begins by choosing to garden for winter interest.

Coneflowers lose little appeal in winter

You garden for winter interest expecting and looking forward to the days of cold. It's not much different than planning your plantings to enjoy the color and texture and size of varied plants during their prime growing time. By gardening for winter interest you imagine how the same plants will look when covered with frost or ice or snow. You anticipate how they will appear when dead or dormant.

On cloudy, gloomy days the brown and plain foliage of dead flowers, grasses, and shrubs can be quite dreary. I'll grant you that. The same can be said of new, plain growth during dark, rainy days in spring. But just as the returning sun creates a vibrant display of color and excitement when it glistens on the dew and raindrops nestling on the young plants, the remnants of a winter storm can transform the garden into a brilliant, magical wonderland.

Sun-loving Heliopsis covered in crystals

When the wonderful combination of frigid temperatures and moist air combine appropriately, a cold night meets a sunny morning with ice crystals covering the landscape. The dreary brown plants are transformed into shimmering, diamond encrusted works of natural art. This is when the garden offers beauty that competes dramatically with the highlights of summer.

Gardening for winter interest has a few basic steps. First is the selection of appropriate plants.  Some plants that provide a strong presence in a spring or summer garden, like Hostas, Lilies, and Irises, have their flowers and leaves wither away with the cold temperatures of fall; there is little left of them in winter. Selecting plants whose physical structure can stand up to strong winds, freezing weather, and heavy snow allows the winter garden to exist. At this point I'm not talking about plants that can survive and live in the cold, but about plants with sturdy stalks, and flowers, and branches after the green life has faded. Plants that offer height above the blanket of snow and ice are better than low plantings that will be covered and unappreciated.

Sunflowers bloom with icy flowers

In my garden, sunflowers, coneflowers, Yarrow, Heliopsis, and Kniphofia offer great scaffolds for the natural ice and snow sculptures of winter. Ornamental grasses and shrubs and bushes anchor the garden when snow falls.

Some plants like Red Twig Dogwood and Burning Bush are at their best in winter as they display dynamic reds against the white snow. Plants with yellow, red, and purple branches are readily available to add a rainbow of color that is often missing in a typical gardener's winter yard once green leaves have disappeared.


Of course plant selection for winter interest does include life; you can think beyond the death of plants and how they look in that state. Ornamental Kale can survive harsh conditions in many regions and displays beautiful greens and purples and reds even when covered in ice. Witch Hazel is a large shrub that flowers in winter. Holly with its evergreen leaves and berries welcomes Christmas with green and red. The parasitic evergreen plant Mistletoe achieved its mythical powers because of its colorful winter state. Mountain Laurels and Yews are evergreens many gardeners overlook in their landscape. There are many colorful winter plants available for your garden.

The second in gardening for winter interest is to leave your plants in place through the cold months. Many gardeners are anxious to clean up their beds as soon as the first freeze fades the foliage. They hack at and pull up the dead, dying, and dormant plants and cart them away. They rake fallen leaves into bags and leave the garden barren, ready for spring planting.  There is nothing wrong with gardening this way, but when old man winter arrives with his brush and palette there is no canvas to receive the artwork.

Ornamental grass shimmering in the winter sun

Besides giving birds and wildlife food and cover in winter, leaving your plants in place will add visual variety to your landscape. The textures and shapes of bare plants after their leaves are gone can only be appreciated during the shortest days of the year. There will be time to clean up the garden in spring when the winter appeal wanes.

Delaying pruning is easy to do. Leave excess branches on trees in early winter. Don't cut the stalks of perennial flowers. The erratic and ungainly growth of flower and shrubs pose nicely in frigid weather.

Simply selecting plants based on how they will look in winter and then leaving them to compose their own beauty is all that is needed to create a garden with winter interest.

To begin next year's winter garden look at your landscape and those of your friends and neighbors. Do you have a spot that is glaringly bare and lifeless in winter? Do you see something that stands out as brilliant in another's landscape? Tour a local botanical garden for ideas. Take the time to observe plants in winter. Think beyond the color and life of summer.

Even my garden art glistens after a frost

During the dark days of winter cold, gardeners often fail to see their garden's beauty, focused on how it will look when the flowers return. While I fall into this pattern too, it only takes an ice storm or cold morning fog to awaken a sense of wonderment. Traipsing through the snow, hearing the sharp crunch of ice, I peer into the world of Jack Frost. It's amazing how a garden can feel so alive when so little is actually growing. It's all about the icy visuals and sustaining your garden for winter interest.

Winter Watering

As fall turns to winter, many gardeners enter hibernation mode. The garden colors have faded, annuals have died, and perennials are muted in dormancy. With gardens quiet and at rest, it's easy for a gardener to enter the same pattern. This relaxation and lack of action can have a devastating effect on plants.

Many tree, grass, shrub, and perennial roots remain viable during cold weather. That means they still need water. In many regions snow fall and occasional rain are enough to provide adequate moisture but during and after prolonged bouts of dry weather or drought it's possible and likely that soil can dry out and the roots will be damaged. Any plant with a shallow root system is at threat and supplemental watering becomes a requirement if you want your plants to survive winter.

Lawns can be particularly susceptible to winter kill, the damage or death of plants in winter. Most cool season grasses can handle cold temperatures and snow cover, but when they encounter desiccating winds and sustained warm winter temperatures, dormant or semi-dormant turf grass can be injured and killed.

Light snow may not be enough for lawns

Newly-planted trees and shrubs are also susceptible to injury in the same weather conditions. They typically require more water than established plants until their root systems become strong enough to sustain them, a period that takes one to two years, and dry winter conditions can be deadly.

Perennials, particularly new transplants, that are exposed to winds and full sun can quickly dry out. Potted perennials are especially at risk.

Daisies can remain alive and green throughout winter

Watering in late fall, winter, and early spring should be a regular part of your gardening activities. Heavy snowfall mitigates the need, but watering may still be necessary. Snow in cold weather actually holds less moisture than commonly believed. Ten inches of snow at the peak of winter only holds about one inch of water. If your storms drop an inch or two of snow, there is hardly any moisture present and when brief snows are followed by long periods with no snow plants are effectively exposed to desert conditions.

Not every day is a good watering day, even if plants need it. You should only water when the outside air temperature is above 40F degrees (4C). The soil should not be frozen or covered with snow.

Also, try to water around noon. The air is above freezing and that will allow the water time to soak into the soil and avoid the possibility of freezing into an ice layer at night. Compacted soil, typical in many lawns, may need a second watering to ensure water soaks into the soil without running off.

Watering slowly by hand is usually the best method to help ensure the water soaks in. Soaker hoses and drip systems may be good during the warm season but in winter any residual water can freeze quickly, thaw slowly, and render them ineffective. A sprinkler on a hose works well for lawns, but be sure that the hose is completely drained after use or you'll encounter the same problem when you reach for it again.

Look closely at your landscape to identify areas that need supplemental winter water. Areas with south-facing walls can dry out quickly due to reflective heat. Snow can remain under the shade of a tree, but the roots can extend well beyond that into dry zones. High spots can receive more sun and wind and be the first to dry. Note where the snow melts first and that will probably be the same spot that needs extra water first. Mulched plants usually need less water but when the soil is dry beneath the mulch watering is needed.

Generally, trees need about ten gallons (38 liters) for each inch (2.5 cm) diameter of the trunk. That means a four-inch thick (10 cm) tree requires forty gallons (150 liters) of water. Thankfully that amount only needs to be supplied once a month in winter; young trees may need two waterings. This ensures the water soaks in to the depth that the roots are growing in an area encompassing the drip zone and beyond. This is a total amount of water and can be reduced by the level of snow or rain.

Small, established shrubs (less than three feet or one meter high) require about five gallons (19 liters) of water per month. The amount increases to about 18 gallons (68 liters) to shrubs taller than six feet or two meters. Newly-planted shrubs need twice that amount.

Many established perennials can handle dry conditions for prolonged cold periods but when sustained warm winter days combine with dry weather, watering is advised. Potted plants will dry out faster and should be the first to receive supplemental water. The amount of water varies with the size of the plant so provide a good soaking once or twice a month. Plants that you put in the ground in fall will probably need at least twice that much.

Some herbs can stay green in winter after others are dead

You don't have to water in winter. Many plants have naturally adapted to varying winter conditions. But your garden plants may not be native to your region and probably don't have those natural adaptations. If you choose to avoid winter watering you're also choosing to place those plants under stress that can cause damage and death.

I've talked with many people who find large patches of turf dead in the spring. Others wonder why so many of their flowers or shrubs don't survive the winter. All around town I see trees where only half is alive and growing. This can all be attributed to winter kill. Sure, I live in a region with harsh, dry winters, but the solution for me and so many others is supplemental watering.

It takes extra effort to pull the hose out on a cool day, spend the time to water each plant, thoroughly drain the hose afterward, and put it all away, but for the two or three times it may be necessary over the course of winter it can save countless hours later. Pruning unnecessarily dead and damaged branches, replacing flowers and sod, and removing dried-out bushes is work that few gardeners look forward to doing. A simple application of water when plants need it most, in winter, can be a life saver, literally.

As fall turns to winter, many gardeners enter hibernation mode. The garden colors have faded, annuals have died, and perennials are muted in dormancy. With gardens quiet and at rest, it's easy for a gardener to enter the same pattern. This relaxation and lack of action can have a devastating effect on plants.

Many tree, grass, shrub, and perennial roots remain viable during cold weather. That means they still need water. In many regions snow fall and occasional rain are enough to provide adequate moisture but during and after prolonged bouts of dry weather or drought it's possible and likely that soil can dry out and the roots will be damaged. Any plant with a shallow root system is at threat and supplemental watering becomes a requirement if you want your plants to survive winter.

Lawns can be particularly susceptible to winter kill, the damage or death of plants in winter. Most cool season grasses can handle cold temperatures and snow cover, but when they encounter desiccating winds and sustained warm winter temperatures, dormant or semi-dormant turf grass can be injured and killed.

Light snow may not be enough for lawns

Newly-planted trees and shrubs are also susceptible to injury in the same weather conditions. They typically require more water than established plants until their root systems become strong enough to sustain them, a period that takes one to two years, and dry winter conditions can be deadly.

Perennials, particularly new transplants, that are exposed to winds and full sun can quickly dry out. Potted perennials are especially at risk.

Daisies can remain alive and green throughout winter

Watering in late fall, winter, and early spring should be a regular part of your gardening activities. Heavy snowfall mitigates the need, but watering may still be necessary. Snow in cold weather actually holds less moisture than commonly believed. Ten inches of snow at the peak of winter only holds about one inch of water. If your storms drop an inch or two of snow, there is hardly any moisture present and when brief snows are followed by long periods with no snow plants are effectively exposed to desert conditions.

Not every day is a good watering day, even if plants need it. You should only water when the outside air temperature is above 40F degrees (4C). The soil should not be frozen or covered with snow.

Also, try to water around noon. The air is above freezing and that will allow the water time to soak into the soil and avoid the possibility of freezing into an ice layer at night. Compacted soil, typical in many lawns, may need a second watering to ensure water soaks into the soil without running off.

Watering slowly by hand is usually the best method to help ensure the water soaks in. Soaker hoses and drip systems may be good during the warm season but in winter any residual water can freeze quickly, thaw slowly, and render them ineffective. A sprinkler on a hose works well for lawns, but be sure that the hose is completely drained after use or you'll encounter the same problem when you reach for it again.

Look closely at your landscape to identify areas that need supplemental winter water. Areas with south-facing walls can dry out quickly due to reflective heat. Snow can remain under the shade of a tree, but the roots can extend well beyond that into dry zones. High spots can receive more sun and wind and be the first to dry. Note where the snow melts first and that will probably be the same spot that needs extra water first. Mulched plants usually need less water but when the soil is dry beneath the mulch watering is needed.

Generally, trees need about ten gallons (38 liters) for each inch (2.5 cm) diameter of the trunk. That means a four-inch thick (10 cm) tree requires forty gallons (150 liters) of water. Thankfully that amount only needs to be supplied once a month in winter; young trees may need two waterings. This ensures the water soaks in to the depth that the roots are growing in an area encompassing the drip zone and beyond. This is a total amount of water and can be reduced by the level of snow or rain.

Small, established shrubs (less than three feet or one meter high) require about five gallons (19 liters) of water per month. The amount increases to about 18 gallons (68 liters) to shrubs taller than six feet or two meters. Newly-planted shrubs need twice that amount.

Many established perennials can handle dry conditions for prolonged cold periods but when sustained warm winter days combine with dry weather, watering is advised. Potted plants will dry out faster and should be the first to receive supplemental water. The amount of water varies with the size of the plant so provide a good soaking once or twice a month. Plants that you put in the ground in fall will probably need at least twice that much.

Some herbs can stay green in winter after others are dead

You don't have to water in winter. Many plants have naturally adapted to varying winter conditions. But your garden plants may not be native to your region and probably don't have those natural adaptations. If you choose to avoid winter watering you're also choosing to place those plants under stress that can cause damage and death.

I've talked with many people who find large patches of turf dead in the spring. Others wonder why so many of their flowers or shrubs don't survive the winter. All around town I see trees where only half is alive and growing. This can all be attributed to winter kill. Sure, I live in a region with harsh, dry winters, but the solution for me and so many others is supplemental watering.

It takes extra effort to pull the hose out on a cool day, spend the time to water each plant, thoroughly drain the hose afterward, and put it all away, but for the two or three times it may be necessary over the course of winter it can save countless hours later. Pruning unnecessarily dead and damaged branches, replacing flowers and sod, and removing dried-out bushes is work that few gardeners look forward to doing. A simple application of water when plants need it most, in winter, can be a life saver, literally.

Fall Clean Up for the Vegetable Garden

Much of my garden is looking pretty ragged and it's time to deal with it. While I advocate leaving flowers and decorative grasses in place through the winter as food and protection for birds and for their interesting wintry appearance, vegetable beds are often best when cleaned up before the ground freezes. Fall clean up is an important chore in most gardens.

An unsightly garden

There are many reasons to clean up the vegetable garden in the fall: most of the chores associated with growing and harvesting are complete but the days are still warm enough to work outside; dead and dying vegetable plants rarely have the same positive visual appeal of flowers and grasses; vegetable plant material left in the garden to overwinter can often harbor harmful insects; weeds can be pulled before they spread in spring; organic material added to the soil can decompose through the winter and early spring; the garden beds will be ready for spring planting with minimal preparation.

Fall is a great time to work in the garden. Daytime temperatures can be warm enough to work comfortably without the heat stress of summer and the soil is warm enough to handle digging and amending. You've had the entire growing season to identify things you want to do and change in your garden and those thoughts are still fresh in your mind while all of your tools and supplies are still in place. Take advantage of that and get outside before the cold of winter keeps you cooped up in the house.

After the first frost kills your warm season plants and subsequent freezes finish off the others, the withered vegetation can become a blight in your landscape. Gone are the vibrant colors and verdant backgrounds. Solely from an aesthetic perspective, removing the plant carcasses makes an immediate positive impact.

Most of the dead plants should find their way to your compost pile; chopping or cutting them into smaller pieces will hasten decomposition. Tomatoes and potatoes are best carted off in the trash, especially if you had any problem with fungal or bacterial infections. If you compost tomato plants with a disease you will introduce that same problem to future plantings when you spread the compost.

Bags of tomato plants

Dead plants left in place through the winter provide a haven for many insects, most of them harmful. They burrow into the plants, or just under the soil, and continue their life cycle that results in many more insects emerging in spring. Cleaning up your beds breaks the cycle and reduces your insect pest problems the next year.

Cool season plants will continue to grow in cold weather and don't need to be removed right away. Leaving brassica plants like cabbage, kale, broccoli, Brussels sprouts, cauliflower, and radishes is a natural way to kill some insect pests. The vegetation attracts some harmful insects. After harsh winter temperatures finally kill them and the plants begin to decompose in early spring, they'll actually release cyanide compounds that will kill those pests. You can pull them up and add them to the compost pile in spring.

If you don't have a compost pile, the debris of fall creates a great start. Stack the dead plants in your designated area and you now have a compost pile. Add the leaves that are piling up on your lawn and kitchen scraps you used to throw away. You probably won't have the perfect blend of material to allow decomposition during the cold temperatures of winter, but you'll have a mass that will begin to turn into compost with the warmth and rain of spring.


With your beds cleaned up, it's easy to see the perennial weeds that have been lurking under cover. Left unchecked those weeds will grow, set seed, and multiply before you return for spring planting. The soil is still workable so deal with those invaders now. Dig them up and throw them on your compost pile. The green of the weeds is a nice balance to the brown of the dead plants.

I add to my compost pile throughout the year and at the end of the growing season I usually have a batch of compost ready to use. With the beds cleaned up I add a layer of that compost to the surface. Along with the straw and grass I used as mulch, it is a great organic amendment to the soil. Aged manure works well too. This year I also added the bedding and droppings from my neighbor's rabbits that have been aging in a pile all summer. Store-bought compost and soil amendments are a good alternative.

Compost on top of straw

With all of those organics in place I simply turn them into the soil with a spade. Through earthworm and microorganism activity the material will break down and decompose. The freeze-thaw cycle of winter will help incorporate it in the soil. It will be about six months until I plant again and in that time the soil will be improved greatly.

In a few hours my vegetable garden is ready for spring planting. Sure the task is completed months ahead of time, but when the air and soil temperatures are finally warm enough in early spring I want to get to planting. Cleaning up the withered plants in spring is an unnecessary delay.

Raised beds ready for spring planting

My vegetable garden is just about on autopilot right now. The garlic is planted and beginning to sprout under the straw mulch; it will be fine through the winter (see my blog, "How to Plant Garlic"). The beds I cleaned up have the organic material incorporated in the soil and are ready to support new growth next season. My green manure, the cover crops (see my blog "Try Green Manure"), are growing well and will be turned in to the soil in spring. I'm leaving the sunflowers in place to feed the birds.

There are many activities to keep me busy now and in the months ahead, but an entire garden, the vegetable garden, is put to bed for winter. It required effort, though it wasn't hard. In a small way I can relax a little as I focus on other things. And it's a nice feeling to look back on the season from first seed to last plant on the compost pile and think about all the enjoyment it provided.

 

Much of my garden is looking pretty ragged and it's time to deal with it. While I advocate leaving flowers and decorative grasses in place through the winter as food and protection for birds and for their interesting wintry appearance, vegetable beds are often best when cleaned up before the ground freezes. Fall clean up is an important chore in most gardens.

An unsightly garden

There are many reasons to clean up the vegetable garden in the fall: most of the chores associated with growing and harvesting are complete but the days are still warm enough to work outside; dead and dying vegetable plants rarely have the same positive visual appeal of flowers and grasses; vegetable plant material left in the garden to overwinter can often harbor harmful insects; weeds can be pulled before they spread in spring; organic material added to the soil can decompose through the winter and early spring; the garden beds will be ready for spring planting with minimal preparation.

Fall is a great time to work in the garden. Daytime temperatures can be warm enough to work comfortably without the heat stress of summer and the soil is warm enough to handle digging and amending. You've had the entire growing season to identify things you want to do and change in your garden and those thoughts are still fresh in your mind while all of your tools and supplies are still in place. Take advantage of that and get outside before the cold of winter keeps you cooped up in the house.

After the first frost kills your warm season plants and subsequent freezes finish off the others, the withered vegetation can become a blight in your landscape. Gone are the vibrant colors and verdant backgrounds. Solely from an aesthetic perspective, removing the plant carcasses makes an immediate positive impact.

Most of the dead plants should find their way to your compost pile; chopping or cutting them into smaller pieces will hasten decomposition. Tomatoes and potatoes are best carted off in the trash, especially if you had any problem with fungal or bacterial infections. If you compost tomato plants with a disease you will introduce that same problem to future plantings when you spread the compost.

Bags of tomato plants

Dead plants left in place through the winter provide a haven for many insects, most of them harmful. They burrow into the plants, or just under the soil, and continue their life cycle that results in many more insects emerging in spring. Cleaning up your beds breaks the cycle and reduces your insect pest problems the next year.

Cool season plants will continue to grow in cold weather and don't need to be removed right away. Leaving brassica plants like cabbage, kale, broccoli, Brussels sprouts, cauliflower, and radishes is a natural way to kill some insect pests. The vegetation attracts some harmful insects. After harsh winter temperatures finally kill them and the plants begin to decompose in early spring, they'll actually release cyanide compounds that will kill those pests. You can pull them up and add them to the compost pile in spring.

If you don't have a compost pile, the debris of fall creates a great start. Stack the dead plants in your designated area and you now have a compost pile. Add the leaves that are piling up on your lawn and kitchen scraps you used to throw away. You probably won't have the perfect blend of material to allow decomposition during the cold temperatures of winter, but you'll have a mass that will begin to turn into compost with the warmth and rain of spring.


With your beds cleaned up, it's easy to see the perennial weeds that have been lurking under cover. Left unchecked those weeds will grow, set seed, and multiply before you return for spring planting. The soil is still workable so deal with those invaders now. Dig them up and throw them on your compost pile. The green of the weeds is a nice balance to the brown of the dead plants.

I add to my compost pile throughout the year and at the end of the growing season I usually have a batch of compost ready to use. With the beds cleaned up I add a layer of that compost to the surface. Along with the straw and grass I used as mulch, it is a great organic amendment to the soil. Aged manure works well too. This year I also added the bedding and droppings from my neighbor's rabbits that have been aging in a pile all summer. Store-bought compost and soil amendments are a good alternative.

Compost on top of straw

With all of those organics in place I simply turn them into the soil with a spade. Through earthworm and microorganism activity the material will break down and decompose. The freeze-thaw cycle of winter will help incorporate it in the soil. It will be about six months until I plant again and in that time the soil will be improved greatly.

In a few hours my vegetable garden is ready for spring planting. Sure the task is completed months ahead of time, but when the air and soil temperatures are finally warm enough in early spring I want to get to planting. Cleaning up the withered plants in spring is an unnecessary delay.

Raised beds ready for spring planting

My vegetable garden is just about on autopilot right now. The garlic is planted and beginning to sprout under the straw mulch; it will be fine through the winter (see my blog, "How to Plant Garlic"). The beds I cleaned up have the organic material incorporated in the soil and are ready to support new growth next season. My green manure, the cover crops (see my blog "Try Green Manure"), are growing well and will be turned in to the soil in spring. I'm leaving the sunflowers in place to feed the birds.

There are many activities to keep me busy now and in the months ahead, but an entire garden, the vegetable garden, is put to bed for winter. It required effort, though it wasn't hard. In a small way I can relax a little as I focus on other things. And it's a nice feeling to look back on the season from first seed to last plant on the compost pile and think about all the enjoyment it provided.

 

How to Extend Your Growing Season in the Fall

Freezing temperatures are coming, if they haven't hit you already. While my high-altitude garden had its first frost about two weeks ago, the vast region that surrounds me is expecting the first fall temperatures below freezing tonight. The first frost of fall can spell doom to many of the warm season plants in the garden, but for gardeners who want to extend the growing season a few weeks it's relatively easy to buy more time.

The basic concept behind growing season extension is to cover plants. You want to put a blanket on your plants to keep them warm. It sounds simple and easy and it is.

An old blanket over a tomato cage

After months of hot spring and summer days, the soil is warm and still capable of supporting most plant root, leaf, and fruit growth. When air temperatures begin to drop in fall many soils are still able to retain the heat that has accumulated deep in the earth until long after the first frost. The key to extending the growing season is to harness that soil warmth. A blanket on the plants does that.

At night in our cozy beds a blanket keeps us warm. Wool, cotton, or polyester, the blanket doesn't actually create higher temperatures. The blanket traps our body heat and radiates it back to our chilled skin. Our own body is what keeps us warm when we cover it with a blanket. In the garden a blanket keeps the plants warm in the same manner by trapping and returning the heat of the soil.

Plants aren't picky about the blanket material. It can be plastic, canvas, wood, or cloth. Of primary importance is that you cover plants before the temperatures approach or drop below freezing.

When you suspect or expect cold temperatures overnight, apply the blanket while the outside air temperature is still above freezing. This usually means during the day when the sun is shining. The waning daytime heat will couple with the radiating soil heat and create a warm air pocket that protects the plant during the cold temperatures.

Like a blanket on our own beds, the garden blanket should fully cover the garden bed that you want to keep warm. It should be large enough to ensure no leaves or plant parts are sticking out from the edges. Any part of the plant that is exposed to freezing temperatures may experience freeze damage. Your foot gets cold when you dangle it outside the covers; the same happens with dangling stems and leaves.

This tarp isn't covering the entire plant

The blanket doesn't need to physically touch the plant and in many cases it should be supported above it. It all depends on the blanket material. I've thrown old wool blankets directly on top of squash plants to protect them from cold. I've leaned a plywood sheet on a fence to cover plants with a lean-to. I've draped both canvas and poly tarps over bushes. But when I use plastic sheeting I use wooden stakes and metal or plastic tubing to support it above the plant; the plastic is thin and any leaves that touch the plastic can experience frost damage as though they were unprotected.

Covering a tomato plant with plastic

In this respect, think of the plastic blanket as an umbrella that envelops the garden bed. We're trying to trap the soil warmth and it's that heat that keeps the plant warm not the actual blanket. Cloth and wood blankets can touch the plant with little damage but plastic isn't thick enough or dense enough to prevent it. I use a lot of plastic to protect my plants and my system is essentially a series of plastic umbrellas or tunnels. The same plastic hoops that allow me to begin planting in early spring are reused to extend the growing season in fall.

Protecting pumpkin plants

Also important in covering the plants is to ensure all edges of the blanket or umbrella are flush with the soil. It's difficult to keep your bedroom warm if you leave the window open. It's equally difficult to maintain a pocket of warmth around your plant if you have one side of the blanket open to the cold air. Use bricks or rocks to weigh the edges down. Bury edges in soil. Clamp or staple plastic to the support system. Drape plastic over the edges of a tarp or a plywood board. You may need to use multiple pieces of material to achieve a complete blanketing.

The last critical component of plant protection is to remove the blanket when temperatures warm up again. Once the sun comes up and temperatures rise above freezing, take the cover off. If you leave the blanket on, you run the risk of potential plant damage through excessive heating. You also want to give the soil more opportunity to warm up again.

You can continue the cycle of covering plants at night and removing the cover during the day for weeks. Until daytime temperatures drop to a point where the soil no longer absorbs heat, you can continue gardening.

Colorado State University conducted studies for extending the growing season in the spring, but the same systems can be used in the fall. They found that a simple cloth covering (a row cover) provided 2F to 4F degrees (1-2C) of protection. That means that the outside air temperature can fall to about 28F degrees (-2C) while the air around the plants stays above freezing. Plastic supported by a metal mesh frame provided 3-6F degrees (3C) of protection. It's important to note that the plastic completely covered the frame, allowing no exchange of air. This is enough protection to keep your plants alive for the first frost of the season and for a few weeks after.

For even more protection, a space blanket, or thermal blanket, is highly effective. The light-weight, metallic blankets reflect up to 99 percent of heat. Adding a space blanket on top of a plastic cover adds protection when the night temperatures drop below the 28F degree (-2C) threshold. In CSU trials, a space blanket added to a plastic-covered frame kept plants from freezing when the night temperature dropped to 0F degrees (-18C), following a sunny, spring day. It is critical to remove it during the day because you've also created an oven that can bake plants in the sun.

If you are really serious about extending the growing season you can take extra efforts to continue gardening when temperatures drop below the point where daytime temperatures can sustain this cycle. You can add a heat source to the plastic umbrella over your plants. Christmas tree lights are one solution, but they need to be the old-style lights, the big ones that heat your fingers when you touch them; new LED lights won't have the same result. The CSU trial showed that a string of C-9 lights draped from the metal frame, under the plastic sheet, added up to 18F degrees (10C) of frost protection. With a space blanket on top, that protection extended up to 30F degrees (16C). That means the outside temperatures can be bone-chilling cold and the plants are still enjoying temperatures above freezing.

Here are a few more thoughts about covering your plants to extend the growing season. Cloth covers work well, but will lose much of their heat retention ability when they get wet; avoid a cloth blanket or sheet if you expect rain or snow.  Heavy tarps or wood sheets retain heat well but can crush plants underneath. Moist soil will retain more heat than dry; plants also prefer moist soil over dry so there's no reason to withhold normal water. Plastic covers can stay in place if you open the edges to avoid over-heating during the day; set up a plastic or wooden frame, drape plastic over it, and just open and close an end during the day-night cycle.

Letting air in during the day

Also, the season-extending technique of covering plants works best with plants that grow close to the ground and for warm season crops. It's not worth the effort and expense to try and blanket a fruit tree. Covering cool season plants like kale, chard, and spinach isn't necessary; they'll keep producing even after there's snow on the ground.

Cover your plants to get past the first frost in fall. Often you only need a few extra days to harvest the crop being threatened by cold. Keep it as simple as you need. One year I didn't see the frost forecast until the nightly news. I ran out as the sun was setting, threw a large tarp over the pumpkin plants, weighed down the edges with rocks, and went back in the house. That was the only crop that needed a little more time to grow. The next morning I pulled off the tarp to see the plant was alive and happy; a few of the leaves that stuck out from the edges were damaged by frost, but I gained enough time for the pumpkins to turn orange in the next week.

At some point in cold-winter regions, the growing season has to end. When you've picked the last zucchini or tomato, there's no reason to protect the plant any longer. Pull off the blankets and plastic and store them away until you need to repeat this process in spring with young plants. By blanketing your plants you can gain time and extend your growing season on both ends.

Freezing temperatures are coming, if they haven't hit you already. While my high-altitude garden had its first frost about two weeks ago, the vast region that surrounds me is expecting the first fall temperatures below freezing tonight. The first frost of fall can spell doom to many of the warm season plants in the garden, but for gardeners who want to extend the growing season a few weeks it's relatively easy to buy more time.

The basic concept behind growing season extension is to cover plants. You want to put a blanket on your plants to keep them warm. It sounds simple and easy and it is.

An old blanket over a tomato cage

After months of hot spring and summer days, the soil is warm and still capable of supporting most plant root, leaf, and fruit growth. When air temperatures begin to drop in fall many soils are still able to retain the heat that has accumulated deep in the earth until long after the first frost. The key to extending the growing season is to harness that soil warmth. A blanket on the plants does that.

At night in our cozy beds a blanket keeps us warm. Wool, cotton, or polyester, the blanket doesn't actually create higher temperatures. The blanket traps our body heat and radiates it back to our chilled skin. Our own body is what keeps us warm when we cover it with a blanket. In the garden a blanket keeps the plants warm in the same manner by trapping and returning the heat of the soil.

Plants aren't picky about the blanket material. It can be plastic, canvas, wood, or cloth. Of primary importance is that you cover plants before the temperatures approach or drop below freezing.

When you suspect or expect cold temperatures overnight, apply the blanket while the outside air temperature is still above freezing. This usually means during the day when the sun is shining. The waning daytime heat will couple with the radiating soil heat and create a warm air pocket that protects the plant during the cold temperatures.

Like a blanket on our own beds, the garden blanket should fully cover the garden bed that you want to keep warm. It should be large enough to ensure no leaves or plant parts are sticking out from the edges. Any part of the plant that is exposed to freezing temperatures may experience freeze damage. Your foot gets cold when you dangle it outside the covers; the same happens with dangling stems and leaves.

This tarp isn't covering the entire plant

The blanket doesn't need to physically touch the plant and in many cases it should be supported above it. It all depends on the blanket material. I've thrown old wool blankets directly on top of squash plants to protect them from cold. I've leaned a plywood sheet on a fence to cover plants with a lean-to. I've draped both canvas and poly tarps over bushes. But when I use plastic sheeting I use wooden stakes and metal or plastic tubing to support it above the plant; the plastic is thin and any leaves that touch the plastic can experience frost damage as though they were unprotected.

Covering a tomato plant with plastic

In this respect, think of the plastic blanket as an umbrella that envelops the garden bed. We're trying to trap the soil warmth and it's that heat that keeps the plant warm not the actual blanket. Cloth and wood blankets can touch the plant with little damage but plastic isn't thick enough or dense enough to prevent it. I use a lot of plastic to protect my plants and my system is essentially a series of plastic umbrellas or tunnels. The same plastic hoops that allow me to begin planting in early spring are reused to extend the growing season in fall.

Protecting pumpkin plants

Also important in covering the plants is to ensure all edges of the blanket or umbrella are flush with the soil. It's difficult to keep your bedroom warm if you leave the window open. It's equally difficult to maintain a pocket of warmth around your plant if you have one side of the blanket open to the cold air. Use bricks or rocks to weigh the edges down. Bury edges in soil. Clamp or staple plastic to the support system. Drape plastic over the edges of a tarp or a plywood board. You may need to use multiple pieces of material to achieve a complete blanketing.

The last critical component of plant protection is to remove the blanket when temperatures warm up again. Once the sun comes up and temperatures rise above freezing, take the cover off. If you leave the blanket on, you run the risk of potential plant damage through excessive heating. You also want to give the soil more opportunity to warm up again.

You can continue the cycle of covering plants at night and removing the cover during the day for weeks. Until daytime temperatures drop to a point where the soil no longer absorbs heat, you can continue gardening.

Colorado State University conducted studies for extending the growing season in the spring, but the same systems can be used in the fall. They found that a simple cloth covering (a row cover) provided 2F to 4F degrees (1-2C) of protection. That means that the outside air temperature can fall to about 28F degrees (-2C) while the air around the plants stays above freezing. Plastic supported by a metal mesh frame provided 3-6F degrees (3C) of protection. It's important to note that the plastic completely covered the frame, allowing no exchange of air. This is enough protection to keep your plants alive for the first frost of the season and for a few weeks after.

For even more protection, a space blanket, or thermal blanket, is highly effective. The light-weight, metallic blankets reflect up to 99 percent of heat. Adding a space blanket on top of a plastic cover adds protection when the night temperatures drop below the 28F degree (-2C) threshold. In CSU trials, a space blanket added to a plastic-covered frame kept plants from freezing when the night temperature dropped to 0F degrees (-18C), following a sunny, spring day. It is critical to remove it during the day because you've also created an oven that can bake plants in the sun.

If you are really serious about extending the growing season you can take extra efforts to continue gardening when temperatures drop below the point where daytime temperatures can sustain this cycle. You can add a heat source to the plastic umbrella over your plants. Christmas tree lights are one solution, but they need to be the old-style lights, the big ones that heat your fingers when you touch them; new LED lights won't have the same result. The CSU trial showed that a string of C-9 lights draped from the metal frame, under the plastic sheet, added up to 18F degrees (10C) of frost protection. With a space blanket on top, that protection extended up to 30F degrees (16C). That means the outside temperatures can be bone-chilling cold and the plants are still enjoying temperatures above freezing.

Here are a few more thoughts about covering your plants to extend the growing season. Cloth covers work well, but will lose much of their heat retention ability when they get wet; avoid a cloth blanket or sheet if you expect rain or snow.  Heavy tarps or wood sheets retain heat well but can crush plants underneath. Moist soil will retain more heat than dry; plants also prefer moist soil over dry so there's no reason to withhold normal water. Plastic covers can stay in place if you open the edges to avoid over-heating during the day; set up a plastic or wooden frame, drape plastic over it, and just open and close an end during the day-night cycle.

Letting air in during the day

Also, the season-extending technique of covering plants works best with plants that grow close to the ground and for warm season crops. It's not worth the effort and expense to try and blanket a fruit tree. Covering cool season plants like kale, chard, and spinach isn't necessary; they'll keep producing even after there's snow on the ground.

Cover your plants to get past the first frost in fall. Often you only need a few extra days to harvest the crop being threatened by cold. Keep it as simple as you need. One year I didn't see the frost forecast until the nightly news. I ran out as the sun was setting, threw a large tarp over the pumpkin plants, weighed down the edges with rocks, and went back in the house. That was the only crop that needed a little more time to grow. The next morning I pulled off the tarp to see the plant was alive and happy; a few of the leaves that stuck out from the edges were damaged by frost, but I gained enough time for the pumpkins to turn orange in the next week.

At some point in cold-winter regions, the growing season has to end. When you've picked the last zucchini or tomato, there's no reason to protect the plant any longer. Pull off the blankets and plastic and store them away until you need to repeat this process in spring with young plants. By blanketing your plants you can gain time and extend your growing season on both ends.