You Can Dig It

Don't be mulch monster — Use it wisely

By Jim Janke | Oct 19, 2016
Photo by: Jim Janke If you mulch like this (on the left), you're going to get this (on this right)!

Mulch makes all the difference in the landscape. This wonderful garden resource can prevent weeds, conserve moisture, improve appearance, minimize erosion, simplify maintenance, and provide winter protection.

But used incorrectly mulch can do a lot of damage. Here are some tips for using mulch correctly around trees and shrubs.

Mulch problems:

— A too-deep layer of mulch suffocates plants by creating a waterlogged, oxygen-deficient soil zone around the roots. Symptoms include yellowing leaves, poor growth and dieback. By the time these symptoms appear, it’s often too late to save the plant.

— Mulches close to the main trunk are great homes for rodents like mice and meadow voles that gnaw on bark at the soil line. Once the trunk has been girdled (more than 50 percent chewed around the circumference) the plant is as good as dead.

— Bark decay is common when mulch is allowed to contact the stem of the plant at or above the soil line. Often the plant appears normal, then suddenly falls over in a high wind because the stem has rotted away.

— Mulches like pine bark and pine needles are quite acidic, and will lower the pH of the area as they decompose. Hardwood mulches start out acidic, but raise the soil’s pH as they decompose, creating the opposite problem.

Guidelines for using mulch:

— Keep the mulch at least 4 inches away from the stem of the plant to prevent bark decay. Discourage rodents by installing a circle of crushed rock around the plant.

— Prevent oxygen deficiency and minimize rodent issues by keeping the mulch depth at 3 inches or less. For our typical poorly drained clay use only an inch or so. Double-ground bark and other fine mulches should also be limited to 1 to 2 inches.

— Consider the pH requirements of the plants being mulched. For example, don’t use hardwood mulch around acid loving plants.

— Every year or two remove the mulch out to the drip line of the plant. If you see exposed roots keep the mulch away from that plant during the growing season.

I use pine bark around trees and shrubs for erosion control, weed control, and appearance. Using pine bark on plants next to the house adds acidity that counteracts leaching of alkaline chemicals from the concrete foundation.

On steep slopes where bark will not stick I use pine straw, anchoring the straw to the hill as necessary with sod staples. These mulches need to be touched up annually, and completely renewed every several years, at considerable expense. So I’m slowly investing in ground covers on these slopes to spend less on mulch.

Jim Janke is an Extension Master Gardener volunteer in Haywood County. For more information call the Haywood County Extension Center at 456-3575. © 2016 NC State University.