Lawn mowers and string trimmers are potentially lethal weapons when used carelessly around trees and shrubs. Young, thin-barked trees are particularly prone to injury. Accidental bumping of a young tree with a lawn mower will bruise and often tear away a section of bark. These damaged areas may become entry points for wood decay fungi. Repeated collisions with a tree may girdle the trunk and result in its death. String trimmers can also be deadly when used around trees and shrubs. The nylon string beating against a tree's trunk will strip bits of bark away and may girdle the tree. Stems of shrubs can also be girdled.
Injury to trees and shrubs can be prevented with prudent care. When planting trees and shrubs, mulch the area around them with 2 to 4 inches of shredded bark, wood chips, or other materials. The mulch helps conserve moisture, control weeds, and reduces injuries due to careless use of lawn mowers and string trimmers. If the grass is growing up to the tree trunk, stay several inches away from the trunk when mowing the lawn. Later, cut the grass around the tree with a pair of grass shears. String trimmers are best used around signs, poles, buildings, underneath fences, and other difficult to mow areas. They should not be used around trees and shrubs.