Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org
Simply place a 2-4 inch layer on top of the soil extending out 4-6 feet from the base of the tree. Be sure to pull the mulch or wood chips away from the base of the tree about one inch. This will keep moles, voles and excess moisture from damaging the roots and the bark of the tree. The finished mulch ring will resemble a doughnut, not a pitchers mound or volcano.
Reapply mulch as needed to maintain a layer no greater than four inches deep. When mulch is applied incorrectly this can set the tree up for many problems in the future. For example, when mulch is too deep, tree roots will be encouraged to grow into the mulch pile and not in the soil where they belong. These roots can be damaged from direct contact of fertilizers, herbicides and seasonal drought.