Wood Mulch is a good source of nutrients and protection for your tree. Once a year the mulch should be turned and new mulch added as needed. Mulch should be applied from the drip line toward the trunk. If this is not practical, minimum mulch circles should be 1.1 feet for small trees, 3.3 feet for medium trees and 9.9 feet for large trees. As beneficial as mulch is, too much can be harmful. The recommended mulching depth is 2 to 4 inches. Mulch should not be piled up around the base or against the trunk of trees. This is called a "mulch volcano".