Mulching around trees offers several benefits, including soil moisture retention, reduced weeding and grass control, and keeping yard equipment a safe distance away from the plants. Shredded bark is a popular mulch to use, which does require periodic touch up as it gradually decomposes. However, I have seen landscapes where bark mulch was routinely added each year whether it was needed or not. This creates a 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 taking it up for decomposition purposes. Consider adding a little nitrogen annually.
- Shoot to maintain a two to three inch layer of mulch. If you feel the need to freshen up the look of the mulch, only apply a very thin additional layer, and strive keep the mulch under three inches deep.
- Don’t pile up mulch against the tree trunk. This keeps the bark moist and more susceptible to disease problems and insect borer attack. Instead create a small doughnut hole near the tree trunk
- Use whatever mulch is handy and visually appealing.
- Pine straw decays rapidly, and can be applied more often than wood or bark chips. It adds acidity to the soil, and so is good around rhododendron, Azalea, pines, and blueberries.
- Mulching material made up of large particles (like chipped wood or bark) 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.