Mulching is one of the best things you can do for the health of trees or shrubs.
Apply mulch starting 6 inches from the base of the tree working out to the desired diameter. Depth should start at 1 inch at the inner circle, increasing to no more than 4 inches (2 inches for clay soils) at the outer edge of the circle.Final depth may be reduced if landscape fabric is placed under the mulch. Also consider using groundcover plants, such as Vinca or Pachysandra, as a mulch alternative.
Additions should be made only to maintain proper depth.
Removal defeats one of the purposes of mulch, which is to decay and mix with the soil.
Fluffing the old mulch before adding more will prevent it from forming a hard surface that deflects water rather than retaining it.
Excessive mulch material piled up against the base of a tree or shrub, a mulch “volcano,” keeps moisture in direct contact with the bark. The moisture penetrates the bark and suffocates the cells of the phloem, which is the layer of living tissue that transfers food up and down the plant. When this supply of food from the leaves is limited, the roots die back, which leads to less water being taken up, and the tree or shrub goes into general decline, leaf drop, and premature death.
Secondary problems, like borers and fungi, move into plants weakened by improper mulching. In sugar maples, the fungal pathogen Phytopthora will move in because of the high moisture around the trunk, creating a canker that girdles the trunk at the base and accelerates the decline of the tree.
Remove excess mulch using a shovel, trowel, or whiskbroom while taking care not to injure the trunk. A hard stream of water may be used to remove excess mulch and soil from the trunk and flare. Cut off secondary roots that may have grown into the mulch. Trunk and flare should be visible. New mulch can then be applied to the proper depth and distance from trunk.