Winter is a time when trees, especially young and thin-barked trees, are damaged by weather directly and indirectly. However, there are proven methods for reducing or eliminating this damage. First, let’s talk about what happens to trees during the winter.
What Happens to Trees During the Winter
Young trees, newly planted trees, and thin-barked trees are most susceptible to a process called sunscald or southwest injury. On a sunny winter day, the bark temperature of your tree can increase 20 degrees higher than the air temperature.
This can cause tree cells to come out of dormancy and become active. When the sun is blocked, shadows cause the bark temperature to drop rapidly or a warm day gives way to near zero temperatures at night. This temperature drop kills these active cells and conducive tissue before they can return to the protection of dormancy.
Once sunscald occurs, cracked areas at the bark level or beneath begin to form which dries out the tree causing leaves or pine needles to appear brown or discolored and bark to die and fall off.
Trees that have been pruned to raise the lower branches, or moved from a shady to a sunny location are also sensitive. Sunscald can kill a tree or make it vulnerable to toppling by snow.
Sunscald can be prevented by wrapping the trunk with a commercial tree wrap. Light-colored wraps work best as darker colors may absorb too much heat. The wrap will reflect the sun and keep the bark at a more constant temperature.
Wrap the trunk from the ground up in an overlapping swirling fashion up to the first branch. Make sure to take it off in early spring or mold and other pests can infect the tree. That said, don’t remove it too early; wait until after the last frost in spring.
Newly planted trees should be wrapped for at least two winters and thin-barked species for up to five years or more until they are established. To repair sun scald damage, cut the dead bark back to live layers. Wrap the trunk in subsequent winters to prevent further damage.
Winter and De-Icing Chemicals
If your tree is within 60 feet of a road or bordering a walkway, salt and other chemicals used for de-icing can cause discoloration, abnormal growth, and long-term die-offs. Magnesium chloride is especially dangerous to evergreens like pine, spruce, and juniper.
Witches broom caused by salt damage. Notice the thickets on the main branch joints
In high-traffic areas, a winter-damaged tree may be characterized by a structure resembling a witch’s broom. Preventing damage from de-icing can be nearly impossible near major arteries.
A plastic fence or shield placed where soil and concrete meet can limit exposure in the root zone of the tree. If you have control over the mixture used to treat icy parking lots and roadways, reducing sodium and adding organic material helps create a more environmentally friendly mix. Choosing a tree species to plant that is hardier is also a wise decision. You may choose to save a tree by transplanting it to a less toxic location, if feasible.
Winter and Animals
Winter food shortages force squirrels and deer to feed on bark, sometimes killing trees and shrubs. Depending on the habitat, providing an alternative food source makes the most sense. Typically, fencing and other obstacles are too costly to install. A squirrel can scale almost every imaginable obstacle to reach a favored tree.
Winter and Heavy Snow
Very wet or otherwise heavy snow can cause permanent tree deformity or toppling. If you know a vulnerable area of your yard, you may choose to assemble a burlap wind and snow screen. It typically stands independent of the tree and blocks snow from getting to the tree. Typical weather patterns must be considered in the placement of a screen or you may find this doesn’t work at all.
Remember, all trees need watering at least once a month throughout the winter. Following this advice will give your trees a greater chance of making it through the winter unscathed.