By Steve Roark
Volunteer Interpreter, Cumberland Gap National Historical Park

Mulching around trees and flower beds offers several benefits, such as soil moisture retention, reduced weeding, and keeping yard equipment a safe distance away from plants. Shredded bark is a popular mulch to use, which requires periodic touch up as it gradually decomposes. However, I have seen landscapes where a lot of mulch was routinely added every year whether it was needed or not, creating an overly thick layer of mulch that can injure or even kill the plants you are trying to benefit.

Signs of over mulching may include abnormally small leaves, chlorotic (yellow or off color) foliage, branch dieback, dying grass outside the mulch around the plant, and cankers on the trunk where it touches the mulch.

Here are some hints for proper mulching of trees:

Decaying mulch can create a nitrogen deficiency in the soil due to bacteria and fungi taking it up for decomposing purposes. Consider adding a little nitrogen annually.
Shoot to maintain a 2-3 inch layer of mulch. If you feel the need to freshen up the look of the mulch, only apply a thin additional layer, and strive keep the mulch under four inches deep.
To protect the tree from mowing equipment, establish a mulch bed at least three feet in diameter.
Don’t apply mulch against the tree trunk. Doing so keeps the bark moist and more susceptible to disease and insect borer attack. Instead, create a small doughnut hole around the tree trunk to prevent contact.
Use whatever mulch is handy and visually appealing.
Pine straw decays rapidly and can be applied more often than wood chips or shredded bark. The pine needles add acidity to the soil, and so is good around rhododendron, azalea, pines, and blueberries.
Mulching material made up of biggish particles, such as chipped wood, is beneficial in that it decomposes slower and allows water to flow freely through it. Fine particle mulch such as shredded bark can pack together so tightly that water cannot reach the soil below, which can cause the tree to become dehydrated.