Two to four inches of mulch around the base of a tree or a group of trees may not only improve appearance but can also improve the general health of the trees by moderating soil temperatures, increasing available soil water, reducing weed competition, and protecting the base of the tree from mower and other equipment damage. Organic mulches, such as tree bark, are preferred as they influence the environment more than inorganic mulches. Taper the mulch depth to one inch near the base of the trees to minimize the risk of root crown rot. Usually mulch applications around trees should be no more than four inches deep. Deeper applications can create undesirable soil conditions.
Mulch-induced nitrogen deficiencies can be caused by fine organic mulches such as sawdust and shredded hardwood bark. When this happens, soil nitrogen is tied up in the bodies of the microorganisms as they break down the mulch and nitrogen is temporarily unavailable for use by trees and other plants growing in the soil. Adding two pounds of nitrogen per 1,000 square feet on the soil surface prior to mulching will minimize this problem.