News release: Protecting trees & shrubs from injury this winter, Part II

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640

Release Date: November 13, 2014

Headline: Protecting trees & shrubs from injury this winter, Part II

In my last column, I discussed how to protect your trees and shrubs from animals, along with some general factors such as the timing of pruning, mulch, and the use of snow melters. This week, I would like to discuss specific considerations of winter protection for evergreens and deciduous trees.

The key fact to remember about evergreen trees and shrubs is that they continue to need water all winter long. The vascular systems of plants are fascinating… the roots take in water, the water then moves up through the plant through the xylem, and finally the leaves transpire the water out of the plant into the atmosphere.  While that process is certainly more active in warm weather, it doesn’t shut down in evergreen species during the winter.  Those leaves are still calling for water from the roots, even when it’s cold.

If the water isn’t there in sufficient quantities, the plant suffers. That means that if the winter is dry, you may need to add water. It’s best to start out in the fall with a well-watered soil profile, if possible. Remember, however, that if the ground is frozen… along with the water it contains, the roots can’t take up water very well.

If the plant is short of water, and when winter winds come around, the plant may suffer from desiccation.  One solution to this is to apply anti-desiccants to the tree in late fall.

In contrast to evergreens, deciduous trees have lost their leaves by the time winter hits, and water demands are almost non-existent. However deciduous trees have their own set of problems to deal with.

The main problem is what we often call Southwest Injury. While the plant has undergone many processes to protect itself from freezing, there are certain conditions that will damage trees. This is especially important for young, thin-barked trees.

Think of a cold, but sunny January day.  The sun shines on the south side of the tree, thawing it out to some degree.  Then the sun goes down, and the tree re-freezes on that cold, clear January night.  This freeze-thaw cycle is what damages the tree.

As the tree ages, the bark matures and this is less of a problem. However for young trees, a plastic tree wrap is a good idea. Be sure to choose white, since this reflects sunlight, and there is less warming of the tree trunk.  Be sure to remove the tree wrap when spring arrives.

You can also paint the lower portion of the tree with a white latex paint. You might thin it a bit with water. This will also reflect sunlight and minimize damage.

If you would like more information on preventing winter damage in your woody species, please give me a call. I have several guide sheets that will help.