Mulch moderates soil temperatures, keeping roots warmer in winter and cooler in the summer. It also helps sustain soil moisture, reducing the water needs of trees. Mulch inhibits weeds, helps reduce soil erosion, and can improve soil, which improves or maintains tree health. To take advantage of all of the benefits of mulch, follow these tips.
Maintain a 2- to 3-inch layer. Coarse materials, such as pine nuggets, may be applied to a depth of 4 inches, but don’t allow mulch to accumulate to a greater depth. Adding more mulch can harm trees because mulch intercepts rain and irrigation meant for plants’ root systems.
Avoid “volcano mulching.” When mulch is piled against the base of a tree, it holds moisture, encouraging rot in the trunk. It also encourages roots to grow close to the trunk, which can kill the tree if roots grow around the trunk.
Mulch to the drip line or beyond. The mulched area around the tree should be at least 8 feet in diameter. Remember that in a forest environment, a tree’s entire root system (which usually extends well beyond the drip line) would be naturally mulched.
Remove old mulch. Some mulches can become matted, preventing water and air from seeping through. Occasionally (every couple of years), you should remove mulch and soil that is against the trunk, together with any roots growing in the mulch. Remove old mulch before adding fresh mulch to the landscape.