Deb Babcock: Protecting your trees this winter
October 21, 2012
Our really cold, windy winters and intense daily sunshine here in the mountains can damage the trees in our gardens, especially young ones that haven't yet developed a thick, rough bark.
Because we experience such intense sun in the winter, the needles on our evergreen trees often heat up to 50 or 60 degrees during the day. This causes transpiration, or moisture to move to the surface of the needles. Because the ground is frozen, the roots are unable to replace water in the needles. Then when the sun goes down and the wind kicks up, frost and ice crystals form, which can kill the needles. These bright, cold days also can destroy the chlorophyll in the needles causing them to fade and loose their vibrant green coloring.
This sunscald often occurs on the south and west-facing branches. You can protect your evergreens from sunscald with windbreaks, shading or commercial anti-transpirant products designed to keep moisture in evergreen needles (Wilt-Pruf(r) for example). Also a good 3-inch layer of mulch on the ground around the tree 3 to 6 feet in diameter will help conserve the moisture in the soil. And if the soil hasn't frozen yet, you can water the trees, too, to ensure adequate moisture in the root system. Plus, moisture in the soil holds more heat than dry soil allowing the roots to continue providing water to the needles later into the winter.
Sun and wind scald also can happen to the bark of trees with smooth or thin bark, such as Aspens. Also, if you have pruned a tree to remove the lower branches, the newly exposed trunk is susceptible to sun and wind scald since it is no longer shaded by the upper branches. For the first winter or two after transplant, consider wrapping the trunks of these susceptible trees from the ground to the first set of branches. There are commercial tree wraps and plastic tree guards available at our local garden centers, or you may create your own wrap using a light colored material to reflect the sun. Once spring comes, be sure to remove the wrap. For young trees, you may need to wrap them each winter for the first two to three seasons until they develop a thicker bark.
Bark splitting and frost canker are two other problems caused by harsh winters. This often occurs when it gets cold at the surface of the soil and there is no protection for the plant by a covering of snow or mulch. Once it warms up, the dead bark splits from the tree, girdling it and preventing the plant from transporting water and nutrients from the soil to the leaves and branches. Eventually, the entire plant dies. Sometimes the dead bark sinks into the tree forming a canker. (In the spring, you can repair the damage by removing the dead bark around the canker with a clean, sharp knife.) Protect your trees by mulching around the base, but not right up against the tree base where small animals may nest for the winter and cause problems.
Other animals such as deer, rodents and rabbits can cause severe damage by feasting on tree bark during winter months. A plastic tree guard or metal hardware cloth placed around the base of your trees as high as 1 foot above the typical snow line will protect them from another girdling problem.
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Finally, if you have small evergreens and shrubs susceptible to damage from heavy snow and ice, consider wrapping them in burlap or something similar so the snow and ice can't weigh down the branches causing them to break.
Deb Babcock is a volunteer Master Gardener through the CSU Extension Routt County. If you have questions, call 970-879-0825.