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.|
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.