For Release On Or After 06/18/10

By Dan Gill
LSU AgCenter Horticulturist

Recently, a gardener had a problem with her Japanese maple tree. The maintenance crew working on her landscape had gotten too close to the trunk with a string trimmer and removed a lot of the bark. The tree was looking poorly, and she was worried about what to do for it. Unfortunately, the damage was done, and nothing could really be done to help the tree. If the damage was bad enough, the tree was going to die.

Save the bark – save the tree

String trimmers that use a monofilament line for cutting weeds and grass can be damaging to young trees and trees with relatively thin bark. If the trimmer line is allowed to hit the trunk, it will remove part of the bark with each contact. If you’re not careful, you might even remove an entire ring of bark all the way around the trunk, girdling the tree. Mowers pushed hard or dragged around the base of a young tree also can be damaging.

The part of a tree’s circulatory system that carries food from the leaves to the roots, which can make no food for themselves, lies just under the bark. When bark is removed, this tissue is damaged, interfering with the tree’s ability to feed its roots. As the roots are deprived of food, they begin to starve and function poorly. And this leads to a stunted, unhealthy tree. Remove a complete ring of bark, and you may cut off food to the roots altogether. The roots starve to death, and the tree dies.

Open wounds created by mowers and trimmers also provide entry points for disease organisms that can cause infections and decay.

To prevent these problems, don’t allow grass to grow close to the base of young trees for the first three to five years after planting. And for thin-barked trees like Japanese maples and crape myrtles, you must prevent damage their whole lives.

Keep an area at least 2 feet out from the trunk grass-free – and further out is even better. Keep the area mulched to prevent grass and weeds from growing. Any stray weeds can be killed with a quick spray of the herbicide glyphosate, if necessary.

Tree guards placed around the lower part of the trunk of young trees also can be used to prevent this type of damage.

Because shrubs generally are planted in beds, they’re less at risk. But this problem occasionally crops up when ground covers, such as Asiatic jasmine, are trimmed away from the base of shrubs with string trimmers, or when large shrubs like camellias are grown individually in lawn areas.

Whether you maintain your landscape yourself or pay someone to do it for you, don’t let this kind of needless damage happen to your trees and shrubs.

Mulch properly

Speaking of mulching around trees, it must be done properly. Mulch should never be piled up in a mound around the base of the trunk – a practice that’s been dubbed “volcano mulching.” Piling the mulch deeply around the base of the trunk exposes the trunk to dark, moist conditions. The bark was never meant to protect the tree from this kind of environment, and decay organisms can take advantage and invade the trunk.

When mulching trees, the mulch should be spread out in a flat disk about 2 to 4 inches deep and pulled back slightly from the trunk. As the mulch thins out and decays, add more as necessary.

Not only does this protect trees from string trimmers, but keeping the area mulched and free from grass encourages faster growth on young trees. Research indicates that in some cases, trees that were mulched grew twice as fast as trees that were not. The major reason is competition from the grass roots.

Killing with kindness

Over-watering and excessive fertilization are also issues for our landscape plants. When weather has been dry to very dry, most of us get out and water landscape plants and lawns. Keep in mind that it is better to water thoroughly a couple of times a week than to water lightly every day.

During the intense heat of summer, many landscape plants are stressed and become more susceptible to disease problems, especially root rot. Excessive moisture in the soil, which commonly occurs when plants growing in the ground are watered too frequently, is a leading cause of root rot in mid- to late summer. And, unfortunately, root rot is fatal more often than not.

Fertilizing too generously also is not a good idea, but it frequently occurs. Generous amounts of nutrients, particularly nitrogen, stimulate lush, vigorous growth that may look great but also may be more attractive to insect pests or, particularly, disease organisms. Other than when growing annual flowers or vegetables, be moderate in the amount of supplemental nutrients you provide. Moderate growth is often healthier.

Rick Bogren