Protecting Trees Against Winter Damage

It's winter and almost all of the United States has experienced cold weather. Even Florida and Arizona have endured unusual chills. Just as we feel better when we don a warm coat on a gray day, small and young trees can benefit from an extra layer. Thick bark on big trees provides ample winter protection, but thin-barked specimens can be damaged by cold weather patterns.

An obvious crack on an aspen.

Sustained cold temperatures aren't the problem; trees can handle that. It's the sun that causes harm. Just as a freeze-thaw cycle may affect soil and tender roots, cold temperatures and the warming sun of day can damage trees. After a cold night or cold, overcast day, the outer bark cools to that same cold temperature. When the sun finally comes out, it begins to warm the bark, but only on the side facing the sun. The warm bark begins to expand and because of the temperature differential from the backside, can split. This "frost crack" is evident on the south and southwest side of trees.

The sun and heat may also cause the bark to be stimulated and begin growing new cells on just the one side. A quick return of cold temperatures kills the new cells. This pattern causes the bark on the sun-facing side to become sunken or split. This "sun scald" results in an elongated dried, sunken, or cracked section of bark.

Both of these situations result in a wound that makes the tree susceptible to further damage and even death. The weakened area may not protect the tree from additional cold damage; like when you walk into a storm with your coat unzipped. More importantly, during warmer weather the wound is an invitation for insects, fungus, and tree diseases. If the tree isn't strong enough to persevere, it can die.

Wrapping my apple tree.

There are a few things you can do to help counteract this problem. The bark absorbs the heat of the sun, causing the damage. Simple methods of reflecting the sunlight to prevent the warming can be effective. You've probably seen the base of public trees painted white. The white color reflects most of the sun's rays and heat. A better procedure for the same principle, is wrapping the trunk of a young tree with white plastic tape to reflect the sunlight. A light plastic trunk guard works well too.

Only the lower portion of tender trees need to be protected. Branches help shade the trunk, stabilize bark temperature, and reduce sun damage. For this reason, newly-pruned, young or thin-skinned trees may be damaged if not protected. You'll rarely see this kind of bark damage more than a few feet off the ground.

Apple tree wrapped to the first branch.

Ideally you want to wrap a tree in the fall before the severe cold of winter, but it can be done any time, particularly before the bark is damaged. You also want to remove the wrap in spring. If the wrap remains on the tree, excess moisture between the wrap and bark can cause water damage; harmful insects can also live, thrive, and lay eggs in that protected space. After a couple winters young trees should have thick enough bark to prevent problems. Thin barked-trees may need to be wrapped for four or five years, but only during the winter; if you leave a wrap or plastic guard on the tree it can also lead to "girdling" issues where the growing tree is strangled.

Many trees will survive with this type of damage, but if you have a treasured tree like my Gala Apple tree in the photos it will benefit both you and the tree to take the extra precautions against the damaging effects of winter sun.

It's winter and almost all of the United States has experienced cold weather. Even Florida and Arizona have endured unusual chills. Just as we feel better when we don a warm coat on a gray day, small and young trees can benefit from an extra layer. Thick bark on big trees provides ample winter protection, but thin-barked specimens can be damaged by cold weather patterns.

An obvious crack on an aspen.

Sustained cold temperatures aren't the problem; trees can handle that. It's the sun that causes harm. Just as a freeze-thaw cycle may affect soil and tender roots, cold temperatures and the warming sun of day can damage trees. After a cold night or cold, overcast day, the outer bark cools to that same cold temperature. When the sun finally comes out, it begins to warm the bark, but only on the side facing the sun. The warm bark begins to expand and because of the temperature differential from the backside, can split. This "frost crack" is evident on the south and southwest side of trees.

The sun and heat may also cause the bark to be stimulated and begin growing new cells on just the one side. A quick return of cold temperatures kills the new cells. This pattern causes the bark on the sun-facing side to become sunken or split. This "sun scald" results in an elongated dried, sunken, or cracked section of bark.

Both of these situations result in a wound that makes the tree susceptible to further damage and even death. The weakened area may not protect the tree from additional cold damage; like when you walk into a storm with your coat unzipped. More importantly, during warmer weather the wound is an invitation for insects, fungus, and tree diseases. If the tree isn't strong enough to persevere, it can die.

Wrapping my apple tree.

There are a few things you can do to help counteract this problem. The bark absorbs the heat of the sun, causing the damage. Simple methods of reflecting the sunlight to prevent the warming can be effective. You've probably seen the base of public trees painted white. The white color reflects most of the sun's rays and heat. A better procedure for the same principle, is wrapping the trunk of a young tree with white plastic tape to reflect the sunlight. A light plastic trunk guard works well too.

Only the lower portion of tender trees need to be protected. Branches help shade the trunk, stabilize bark temperature, and reduce sun damage. For this reason, newly-pruned, young or thin-skinned trees may be damaged if not protected. You'll rarely see this kind of bark damage more than a few feet off the ground.

Apple tree wrapped to the first branch.

Ideally you want to wrap a tree in the fall before the severe cold of winter, but it can be done any time, particularly before the bark is damaged. You also want to remove the wrap in spring. If the wrap remains on the tree, excess moisture between the wrap and bark can cause water damage; harmful insects can also live, thrive, and lay eggs in that protected space. After a couple winters young trees should have thick enough bark to prevent problems. Thin barked-trees may need to be wrapped for four or five years, but only during the winter; if you leave a wrap or plastic guard on the tree it can also lead to "girdling" issues where the growing tree is strangled.

Many trees will survive with this type of damage, but if you have a treasured tree like my Gala Apple tree in the photos it will benefit both you and the tree to take the extra precautions against the damaging effects of winter sun.