|My raised beds after a recent snow.|
Accompanying the snow were frigid Arctic temperatures. The high temperature yesterday was 20 F with a low of 3 F. The high today is supposed to be 16 F with a low of -4 F. Throw in the wind we had and the wind chill temperatures were well below zero. Of course, our forecast is for temperatures climbing into the high 50s by the end of the week. As the snow piled up in drifts it was easy to think that it was worth enduring the cold in exchange for the water that would find its way into the soil when the snow melts. The problem is that the snow doesn't hold much moisture.
Yesterday my wife commented, "All this snow will be good for the garden." I told her that wasn't the case and spent a few minutes explaining that temperature affects how much water is contained in the snow flakes. Colder air has less water vapor in it and snow flakes formed in Arctic air like we experienced are light and dry. Our snowiest months are March and April and the temperatures during those months supply big, heavy snowflakes laden with water because the warmer air contains more water vapor. Her eyes began to glaze over as I continued, but the point was that all the snow we have blanketing the garden now will have little effect. In fact for many people it may harm their landscape.
Coincidentally, a front page article in The Gazette today highlights the same concern. A standard role of meteorologists is to measure the amount of precipitation in snow. The meteorologists I used to work with explained to me long ago that it takes about 10 inches of snow to equal one inch of measured precipitation, or water. As the temperature drops, the amount of precipitation drops too. Kyle Mozley, a National Weather Service meteorologist, says in today's article that it might take 20 to 30 inches of snow to obtain one inch of precipitation when it's accompanied by below-zero temperatures.
As I've written before, plants still need moisture during the winter, especially when the daytime temperatures occasionally climb into the 50s or 60s. It's easy for gardeners to look at the six inches of snow they have on the garden and think that it equates to a "good watering." In actuality that six inches might only hold 1/5 of an inch of water.
Worse yet, when the sun comes out after a storm, a good portion of that moisture may be lost through sublimation. Sublimation is when a solid substance is transformed directly into a gas without becoming a liquid. On a cold sunny day you can often see this happening as the water vapor departs the snow. When it looks like steam is rising from the snow, that's sublimation in action. Solid water, or ice, is becoming gaseous water, or vapor; the liquid part never happens.
When you combine snow from cold days and nights with sublimation, the moisture in the snow is very low and when it melts the surface may get damp, but not much water finds its way into the soil. If a gardener assumes that the snow is providing necessary winter water, they'll be mistaken and the plants will suffer as a result.
Plants with shallow root systems are the ones that will suffer the most. New trees, shrubs, and perennials haven't established root networks and are relying on your help through a dry winter. The new shrubs and trees may require as much as five or ten gallons of water per month once the temperatures rise above 40 F degrees. Older, larger shrubs may need more than that. Lawns can dry out quickly and you won't be aware of "winter kill" until everything else starts to green in the spring.
This is also a time to look for microclimates again. Plants that get reflective heat from the sun or that receive more wind will dry out faster. You'll notice that the snow melts faster next to your house on the south side. The windswept yard may cause a drift a few feet deep on one end, but in the middle the snow may be virtually absent. Both of those areas have less snow, which means less water, and then warm up faster causing the plants to be drier.
Take a close look at your garden and landscape. Do your own analysis of the snow and precipitation levels for different areas. Once the temperature rises above 40 F degrees and the snow is gone, be ready to go out with your watering can or garden hose. As always, stick your finger in the soil to be sure it isn't still frozen. Try to water your plants around noon so the water has time to soak into the soil before nighttime freezing temperatures come around again.
It takes extra effort, but late winter is when most of the potential damage can occur. Days are starting to get warmer, soil will be more likely to thaw, and snow won't be enough to provide necessary moisture for plants. If the roots are going to dry out and be damaged it's going to happen during days like these.
By the end of the week, when I'm enjoying the return of warm days, I'll be walking through my garden and sticking my finger in the soil next to my perennials, shrubs, and new trees. Mulch helps a lot to retain moisture and my mulched beds may not need much additional water, but I'll be providing it for all of the areas that do. I'll be left with a dirty finger and wet boots, but my plants will be better for it.