Skip to Main Content

Preventing Mechanical Damage to Trees

It may be an overused quote, but an old Ziggy cartoon states, “We have met the enemy, and he is us.” That can certainly relate to the accidental injury we sometimes inflict upon trees when mowing or using string trimmers. The old adage applies, “Prevention is better than cure.”

Of course, other accidental injury will occur when we run into trees with vehicles or equipment, when we install new water lines and prune roots, or a number of other scenarios. But, the most common is simple injury from mowers or trimmers.

A question I occasionally receive is whether trees damaged in this manner will recover. Well, it depends.

To better understand the effects of mechanical injury, let’s cover some tree anatomy and how the tree will attempt to recover. Finally, we’ll cover some prevention strategies.  

Lindsey Purcell, Purdue Urban Forestry Specialist, authored a publication entitled, “Mechanical Damage to Trees: Mowing and Maintenance Equipment.” We’ll lean on Lindsey for some professional advice today.

Of course, mower decks and string trimmers damage the base of the tree at the root flare. This is the area where the trunk flares out atop the main order root system, and this flared area can catch mower decks if the person isn’t paying attention.

Under the bark are vessels which transport sugars, nutrients and water to all parts of the tree. The growth layer of the tree, the cambium, is also just under the bark. “Any damage to this transport system can affect tree health and the tree could die,” said Purcell.

Although some trees have thick bark, some newly planted trees and some particular species of trees have thinner bark. Young, smooth-barked trees are of particular concern for mower and string trimmer damage, and these include birches and maples.

“Any damage to or removal of the bark and the transport system can cause problems for trees,” said Purcell. “Even when a tree tries to recover from a wound, leaves and branches often decline and die back, because food and water pathways were destroyed.” If the damage extends all the way around the tree from multiple injuries, the tree may become girdled, which will result in death.

“All tree wounds are serious when it comes to tree health,” said Purcell. “No matter what size the wound is, the damage done is irreversible.”

Over time, the tree will attempt to seal off, or compartmentalize, wounds. “The wounded area is an opening for wood-rotting organisms and decay fungi to enter and cause further damage,” said Purcell.

Purcell offered some easy and low-cost suggestions to prevent this type of damage. Follow one or more of these suggestions:

  1. Physically remove turf or prevent grass and weeds from growing at the base of the tree.
  2. Spray appropriate herbicides to eliminate vegetation around the base of the tree to decrease mowing maintenance costs. Be sure to use care when applying herbicides around trees, and carefully follow all label directions. (Note: if using a product containing glyphosate around thin-barked trees, you may additionally want to shield the tree from accidental spray coverage.)
  3. Add a mulch ring, when possible, to help the competition for water and nutrients. 2-3 inches over the root zone is adequate; don’t mound mulch up around tree trunk like a volcano. Mulch rings are attractive, reduce mowing requirements, and they are a visual cue to keep mowing equipment away from the tree.
  4. Add trunk guards or similar devices to give the tree additional protection from rodents, equipment and winter damage. Rodent guards and expanding white tree guards are available.

For more information, access Purcell’s publication at

To Top