The objectives, advantages, and disadvantages of mulching, and examples of commonly available products were outlined in the preceding chapter. For extended maintenance of landscape plantings, mulches require replacement. Organic mulches decompose, forming humus and an ideal medium for the germination of newly deposited weed seeds unless mulch is replaced annually. Inorganic mulches do not decompose but decline in appearance if not freshened periodically. Caution: Old mulch should be removed before new is added. Otherwise, the soil level over the roots is gradually deepened and the plants may die. Also, to reduce the possibility of stem and trunk tissue being killed by the heat of decomposing mulch or by bacterial and fungal infection promoted by the moist mulch, the mulch should not be piled against the trunk or crown. It should be kept three to five inches back from shrub crowns and the trunks of young trees. Older trees need at least 8 to 12 inches of mulch-free area.
One important use of mulch is as a protective divider to prevent lawnmower damage to the base of plants (Figure 11-2). A gouge from a mower creates a site for pathogen or insect invasion of the plant. If hit
figure 11-3. A ring of mulch separates the tree from potential mower injury. (Delmar/Cengage Learning)
repeatedly, a tree may become partially or completely girdled. In large landscapes with numerous trees and an understaffed maintenance crew who rely on riding mowers for grass cutting, frequent injury to trees results from attempts to mow as close as possible, thereby eliminating hand trimming. A ring of mulch around the base of each tree can protect the tree, speed the overall mowing time, and create a neat appearance (Figure 11-3).