Published on 02/18/10

Mulch plants, but not too much

By Sharon Dowdy

Dedicated gardeners like to treat their plants like they are their babies. To keep them warm and help them retain water, they surround them with a lot of mulch. But a University of Georgia expert says applying too much to your plants can do more harm than good.

“Mulch is a good thing,” said Henry Hibbs, the University of Georgia Cooperative Extension coordinator in Oconee County, Ga. “It has become essential to the survival of the landscape plants we cherish.”

Fresh woodchips can hurt plants

Hibbs warns that using fresh woodchip mulch piled high and deep can hurt landscape plants.

There are several problems with this practice. First, if fresh woodchips are applied directly in contact with the soil around the plant, it can cause a loss of nitrogen. The plants would typically receive this nitrogen from the soil, he said.

“Fresh woodchips, like those from old Christmas trees, are mostly carbon and will steal nitrogen from the plant’s soil in their urgency to begin composting,” he said.

Hibbs recommends stacking fresh woodchips and allowing them to weather and stabilize for months or even a year before using them as mulch.

Too much mulch can block water

The second problem with piling mulch too deeply around a plant is that this practice can actually prevent water from reaching the plant’s roots.

A third risk is that excessively wet soil held under thick mulch can develop fungal growth and diseases that will damage plants.

“I have recently visited several yards where the deep mulching and excessive water had suffocated the roots and killed the plants it was expected to protect,” Hibbs said. “I guess this falls under the category of the trees being ‘loved to death.’”

Don't encourage rats

Adding too much mulch can attract rodents who view the mulch as the perfect place to set up homestead.

“If the mulch lies against a tree trunk, rodents can chew the bark until the plant is completely girdled, which causes a quick and sudden death to the tree,” he said.

Mulching tips

Hibbs offers the following mulching tips:

1. Apply mulch only 2 to 3 inches deep over plant roots. Only apply as far out as the drip-line.

2. Keep the mulch at least 3 or 4 inches away from the plant base or tree trunk.

3. Avoid applying fresh woodchips until they have aged for at least a few months.

For more gardening tips, contact your local UGA Extension office at 1-800-ASK-UGA1.

Sharon Dowdy is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.

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