FINDING ANSWERS

MULCH MATTERS

Q

Most references recommend mulching around new trees. I like the look of trees surrounded by a green lawn and so have been planting trees, then laying sod over the planting area. As long as I can keep both the tree and lawn watered, what's the harm? — West Virginia

A

There are some very nice landscapes that look like a grove of trees within a grassy area. However, these landscapes are not without problems. First, mowing and string trimming close to the trunk of any tree would result in damage to the trunk. Depending on the species, the damage may be superficial or it may be deep enough that the phloem and xylem are exposed and opened to invasion of pests and dieback in the upper portion of the tree. If nothing else, the mulch is a protector. Secondly, studies have shown that tree roots growing in the same area with turfgrass, are in constant competition with the roots of the turfgrass, especially from Kentucky bluegrass. Kentucky bluegrass has its roots concentrated in the top few inches of soil — the same area newly planted trees are trying to reproduce their root system. In this situation, Kentucky bluegrass roots always win the competition. In one particular recent study, researchers at Utah State University, found that buffalograss did not offer too much competition to newly planted trees, probably because their root system is concentrated twice as deeply as that of Kentucky bluegrass. For the long-term health of the trees, an investment of mulch will pay off nicely.

DROUGHT DOUBT

Q

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On one of my properties, I had a very nice oak tree die during this past summer. The leaves just turned brown and are still hanging on the tree. We experienced quite a drought, but the area was irrigated, so am surprised that the drought killed the tree. Is there any way to tell what happened? — Chicago

A

There are several things to look for while autopsying a tree. Even though Chicago did experience a severe drought this summer, this is probably not what killed the tree. Typically, droughty conditions will cause leaves to shrivel, then brown, then fall off the tree, depending on the severity of the drought and the species of the tree. Some trees shed their leaves early in an attempt to avoid drought stress. However, you mentioned the leaves are still on the tree. This indicates that there was something wrong further down the branch, possibly at the trunk or in the root system. You need to inspect the major branches, the trunk and the roots to find where the damage occurred. This may be the result of diseased roots or trunk, borer damage that disrupts the pipeline or a girdling root that has strangled the trunk. It sounds like it is too late for this tree, but could prompt you to set up a regular inspection program. Examine each tree on your properties and note any differences in the bark; look at the base of the trunk for signs that a root is girdling the trunk or can in the future girdle the trunk; look at the length of branch growth for the past several years; and look for any other signs of trouble.

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