Mulching your trees
Spring Time is Mulch Time
"Spring is a great time to mulch your trees. But no volcanos piled high around the base of the trunks, please! This practice traps moisture around the trunk and the root flare, leading to decay and often structural damage. The best shape is a donut: keep mulches several inches away from the base of the tree to avoid rot and diseases.
Trees with mulched root zones are usually larger, more vigorous, develop faster and have higher rates of survival than plants surrounded by turf grass or bare dirt. Mulches retain soil moisture and reduce erosion and soil compaction. Mulching under trees results in fewer weeds to compete with tree roots for water. Soil under mulch is likely to stay warmer in winter and warms faster in spring, helping extend the growing season for roots.
Organic mulches are a favorite among professionals, who view wood chips as an effective, attractive mulch for trees. Avoid fine mulch, which can become matted and prevent penetration of water and air. A good mulch bed should extend out at least three feet from a tree's trunk in all directions, though extending to the drip line is preferred. The mulch depth should be 2-3 inches.
Don't keep adding new mulch on top of old. Mulch does decompose, but you don't want to accumulate excessive mulch year after year by adding fresh mulch every spring. If you want the look of fresh mulch, and there is less than three inches in depth under the tree, break up the old with a rake and add only a thin layer of new on top."
-- condensed and edited summary of a Town Topics article on 2/16/11 written by Pepper deTuro, certified NJ arborist and PBSTC Advisory Board member