University of Illinois Extension

Lawn Mower Bites Kill Bark

Lawn mowers can do damage to your landscape, warned a University of Illinois Extension horticulture educator.

"The lawn mower was supposed to circle, but instead it struck the base your newly planted sapling. Oops! Is that a problem?," said Nancy Pollard. "Yes it is. Wounds that reach below the bark never heal as skin does. At best, the trunk seals off the injury, but there is no repair in the sense that our skin repairs itself. Bark will form a callus along the edge of the wound, but it rarely can bridge the break. The trunk typically looses the bark in the injured area, and the wound remains decades later." Pollard recommended protecting against lawn mower bites by mulching.

"When planting a new tree, take the time to remove grass at least two feet out from the base," she said. "Put down woodchip mulch to a depth of about three inches. Mulch should ring the tree like a lifesaver, not a volcano. A ring of mulch protects from injury, keeps roots comfortably cool, reduces water loss, and keeps weeds at bay."

The best way is to mulch just to the bottom of the root flare, but do not pile it up the base. If the tree isn't planted too deep, you will see a slight flare where the roots naturally form. Trunk tissue at and above the flare is usually water resistant, not waterproof. If not allowed to dry out, eventually, insects and diseases attack wet bark. "People enthusiastically pile mulch at the base, not knowing it will soak and injure rather than protect the tree," she warned.