JoAnne Skelly: Trees can get sunburn, even in winter

Winter sun and drying winds can damage not only our skin, but the bark of trees and shrubs. It seems obvious that plants might get sunburned in the summer, but less intuitive that it also happens in the winter when it is called winter sunscald. Trunks and young branches that had been shaded by leaves all summer long are now exposed to our high-altitude sun. Winter sunscald primarily affects the south or southwest side of the plant.

Winter sunscald occurs when bark heats up during the day followed by cold temperatures at night. These rapid temperature extremes actually damage bark cells causing cracking or breaks in the bark. Flowering plums are known to suffer severely from winter sunscald. Other susceptible trees include ash, birch, cherry, crabapple, linden, maple and spruce. Younger or newly planted trees are more prone to winter sunscald than older trees. Drought stress increases the likelihood of damage.

The best way to prevent sunscald is to keep trees, particularly young trees, watered well through the winter. Mulch around the trunk with organic mulch to conserve water, but keep the mulch 6 to 12 inches away from the trunk to prevent rodent damage. Tree wraps, such as plastic spiral wraps, will shade a trunk reducing the absorption of heat during the day, making the nighttime variations a little less extreme. Wraps should be white to reflect heat, rather than dark or paper, both of which absorb heat. Extra heat creates more of a temperature fluctuation. Be careful when wrapping. If wraps are applied incorrectly, moisture can collect behind them potentially causing rot damage. Wraps can also harbor insects. Wraps should be removed each spring after the last frost. Although white latex paint works to reflect the sun from the trunk or branches without creating disease or insect problems, once it is applied, it’s permanent and not attractive. Another alternative is temporary fencing to shade the trunk.

I want to thank Greenhouse Garden Center in Carson City for their newsletter, which gave me the idea for this article. I think they even have a class coming up on the topic, so check with them. They certainly have all the best wrap products for trees and the expertise to tell you the appropriate application methods.

Also, think about protecting your evergreens from winter drying. Check out anti-desiccant products, which you apply to keep plants, particularly evergreens, from losing water through their leaves or needles.

JoAnne Skelly is associate professor and Extension educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.