Deb Babcock: Split trunks and sunscald on trees

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Deb Babcock

Deb Babcock's gardening column appears Thursdays in Steamboat Today.

Find more gardening columns here.

After attempting to populate my yard and garden with seedlings from the Forest Service, then with trees dug up from the forest — after obtaining permits — we gradually invested in large trees from local nurseries. And because it is such a big investment, we carefully watch and nurture these to ensure their longevity and health.

So any time one of them starts showing signs of stress, I try to immediately address the problem to avoid losing the tree.

Case in point: Two Canadian chokecherry trees we purchased two years ago emerged from their first winter here with large vertical splits down the center of their trunks. This is common among fruit trees in our mountain community and often is caused by the huge temperature fluctuations we experience, particularly as we go into deep winter or come out of it. Days can be warm and sunny, evenings frigidly cold. Often called ‘frost cracks,’ these splits are not usually fatal to the trees, and indeed, mine came through summer looking fine. But if disease organisms enter the interior of the tree through these bark splits, it could cause decay and eventual death.

Splits also can occur if the tree experiences growth conditions that range from slow growth because of a dry summer to a fast growth spurt followed by wet or normal conditions. Sunscald is another cause of splits. You’ll generally see an outer layer of bark begin to peel away in summer after the winter damage.

Sunscald is caused by hot sun and wind and generally is seen on the south and southwest sides of our trees. On evergreens, the warm winter days cause some cells in the bark and needles to become active and begin respiration. The water that is given off cannot be replaced because the roots are still in frozen soil. Then, when it gets cold at night, the cells are killed. On deciduous trees, the damage generally is seen on the trunk and large branches.

Should you notice sunscald injury or frost cracks in your trees this spring, the best thing to do is prune out any injured foliage in mid-spring and remove any damaged bark back to the healthy tissue. The natural defenses of the tree itself will form a protective callus over the injury. Research has shown that tree-wound paint or tar are of little value when painted over an injury, and in fact, may hinder the recovery of the tree.

On newly planted trees and young trees that have not yet grown a protective sunscreen within their bark, it is a good idea to wrap the trunk each fall and then to remove the wrap in the spring. For evergreens, you can use a spray desiccant to help keep needles from drying out, or wrap the entire tree in burlap.

If you have questions about the trees in your yard, call the Routt County Cooperative Extension Office at 970-879-0825. Staff and the office’s volunteer master gardeners will attempt to diagnose the problem and provide solutions. I’ll be addressing various tree problems in future columns throughout the growing season.

Deb Babcock is a master gardener through the Routt County Cooperative Extension Office. Call 970-879-0825 with questions.

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