Know these garden don’ts

Richard Bogren  |  6/9/2017 1:32:40 PM

By Dan Gill

LSU AgCenter Horticulturist

(06/09/17) Although we try to do the best we can to properly take care of our landscapes, we seem to commonly make a few mistakes. But they’re easily avoided as long as you are aware of the proper way to do things.

Save the bark — save the tree

String trimmers that use a monofilament line for cutting down weeds and grass can be highly damaging to young trees and trees that have relatively thin bark. If the line is allowed to hit the trunk, it will remove part of the bark with each contact. If you are 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 young trees can also be damaging.

The part of a tree’s circulatory system that carries food manufactured by 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 send food to 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, leading to the death of the tree.

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

To prevent these problems, do not 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.

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 has 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 mulch 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.

The right cut

Mowing lawns is a constant chore through the summer. Two common mistakes are mowing too seldom and mowing too short. Not mowing properly can weaken the lawn, leading to turf thinning and weed growth.

Lawns should be mowed weekly during the summer. It is unhealthy to allow the grass to grow tall and then cut it back.

Also, cut your grass at the right height. Mowing too short is damaging to the grass. Mow bermuda and zoysia lawns at about 1 inch, mow centipede lawns at about 2 inches, and mow St. Augustine lawns at about 3 inches.

Killing with kindness

Overwatering and excessive fertilization present two additional problems for 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. Don’t irrigate excessively.

Fertilizing too generously is also not a good idea, but it is frequently done. Generous nutrient levels, particularly nitrogen, stimulate lush vigorous growth that may look great but may also 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.

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Many shade trees are often improperly mulched by piling the mulch around the base of the trunk instead of spreading the mulch. Photo by Allen Owings/LSU AgCenter

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String trimmers can cause significant damage to young trees or those with thin bark. Photo by Dan Gill/LSU AgCenter

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