Lawn Equipment Damage to Trees

— Written By and last updated by Nancie Mandeville
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lawnmower landscaping around trees

When a tree is bumped or scraped by a lawnmower or bark is damaged by a string trimmer, the resulting wound can seriously threaten the life of that tree. Not only is the wound itself damaging, but pathogens can also enter the wound, causing further distress. Microorganisms often attack injured bark and invade the adjacent healthy tissues, greatly enlarging the affected area. It is not unusual for a tree to be completely girdled from microbial attack following damage from a lawnmower or string trimmer. Decay fungi on the surface of the wound can cause structural deterioration and decay of the woody tissues beneath the wound. The resulting internal decay can cause the wounded tree to break off at the stem or root collar.

Lawnmower injuries occur when mower operators attempt to trim grass around trunks with a push or riding mower. String trimmers cut into the bark and there is the potential to girdle a tree if the damage completely encircles the tree. The root collar area is the most common site of injury, though wounds may be found anywhere from the roots to several feet above the ground. To prevent such injuries, turf around trees can be removed and replaced with mulch. Mulching conserves moisture for the tree roots and reduces competition from the surrounding turf.

The most severe injuries from lawn mowers occur during periods when the tree bark “slips” in early spring during leaf emergence and in early fall during leaf drop. During these periods, even minor injuries will produce large wounds. Trees are long-term investments in our landscapes, take care to protect them.

Join the UCEMGV for their Successful Gardener program, Thursday, August 1, at

7 p.m. at the UC Agriculture Center. Steven Stegall will be our speaker and he will be discussing Extending the Growing Season.