Deep winter frost may lead to tree and shrub problems in spring

By Todd Lanigan, forest health specialist, Eau Claire, Todd.Lanigan@wisconsin.gov, 715-210-0150

The first part of the winter of 2018-2019 was rainy and icy and remained pretty much snowless until February. These conditions allowed frost to penetrate deep into the exposed ground, likely causing root injury to trees and shrubs that will manifest as temperatures rise this spring.

At the end of January, the frost depth was two to four feet down and was still two to three feet down in mid-March. Frost at those depths is likely to have caused some root injury to trees and shrubs over the winter.

If there is any root injury, the severity of the damage will influence how the tree or shrub responds in the spring. If there is very little or no damage, the plant should look normal. As the damage increases, you may notice more dead twigs or branches than you would normally see in a healthy plant. These could either be scattered throughout the plant or more heavily concentrated in one part. The plant could also produce less foliage, making it look thinner and more transparent than you would expect. In some cases, the plant may produce very little foliage but have high seed or fruit production. The worst-case scenario for root damage is the tree or shrub will send out new foliage that quickly dies or there is no new growth at all in spring.

Whether or not to remove the injured tree or shrub is up to you. If you know the plant is dead, then removal is a good choice, especially for hazard trees. A hazard tree is a tree that is likely to hit some target (e.g. house, car, shed, picnic table, swing set, etc.) if either the branches or tree were to come down. If you are not dealing with a hazard tree, you may want to let the tree or shrub grow for the summer and re-evaluate after the growing season.

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