What my Needles Wouldn't Do for a Little Water!

Jesse Fulbright, MSU Liberty County Extension

This week, I wanted to address what I think is going on with some of the brown we may be seeing on our evergreens this time of year. 

A lot of our problems come down to what is probably winter desiccation.  Winter desiccation of evergreens is discoloration or damage of the needles.  Winter sun and wind can cause water loss.  Additionally, if the roots are in frozen soil, they are unable to replace the moisture and it will result in browning needles.  It is most common to see the damage on the south, southwest or windward sides of the plant, but the whole plant can be affected in severe cases.  This is more common in young trees.

Photos courtesy of Utah State University Extension.

For our evergreens, the best thing to do to prevent winter desiccation, or at least alleviate some of the more severe damage, is to water all trees and shrubs prior to the soil freezing.  In some winters, when we have chinooks, we also have the opportunity to water then.  Unfortunately, the past few winters haven’t necessarily provided us with many respites between storms.  If your trees are young, you can provide them with some sort of wind or sun barrier, such as burlap stretched between two posts.  However, this only works with younger trees and smaller shrubs, such as the arborvitae we see occasionally around town.  If a person does go with this method, you also need to remember not to cover the entire plant as air needs to continue to circulate around the trees to some extent.
 

 
 
Another problem that might occur around town is with our deciduous trees.  These are ones like our ash, birch, and chokecherry trees.  Bark on the south and southwest sides of tree trunks and in branch crotches may be killed by sunscald.  With sunscald, bark is warmed and the cells in tree de-hardened by afternoon sun.  Rapid temperature drop after sunset then kills the cells and bark. There are several ways to reduce sunscald.  Tree wrap, such as that made from heavy craft paper, can be applied to the trunk in October to reflect the sun and reduce abrupt temperature fluctuations.  This also helps keep rodents from feeding on the bark.  White latex paint also reflects the sun and prevents rapid temperature changes.  Wrap or paint the trunks from the soil line to the lowest branch.  The purpose of tree wraps is not to keep the trunk warm but instead to keep it cool.  Evergreen shrubs interplanted with trees help shade the tree bark during winter and reduce sunscald.

For more information about tree care, either for new or mature trees, the Extension office has a MontGuide titled, “What’s Wrong With This Tree” that is free and available to the public.