Protect Your Trees and Shrubs from Lawnmower Blight

Posted: August 25, 2012

Each year a large number of trees and shrubs in our landscapes are severely injured and die from lawn maintenance equipment. Sadly, those deaths are preventable by keeping lawn mowers and string trimmers away from the trunks of trees and shrubs...

When the stem of a shrub or tree is repeatedly struck by a lawn mower or string trimmer, a wound is created that kills the water and food transport vessels.   That damage is irreversible because woody plants do not “heal” like animals and regenerate new tissues in the same place.  Even small wounds and removal of bark will open the plant to infection by wood rotting organisms such as decay fungi. 

Once wounded, it will take energy from the plant and time to close the wound or “callus over”.   When numerous wounds or nicks are created all the way around the trunk of the young tree or shrub the plant becomes “girdled”.   When the stem is girdled, the leafy crown of the plant will not be able to get water because the conducting tissue or xylem is dead on all sides of the stem.  Conversely, the roots will not be able to get food made in the leaves (photosynthates) because the phloem tissue that is located under the bark is also dead.  


There are three underlying causes of lawnmower damage:  lack of knowledge about how trees grow and the damage equipment like string trimmers can do to trees, lack of accountability for the damage caused, and lack of care when operating equipment around trees.  


The key is preventing lawnmower or string trimmer damage by making the landscapers and equipment operators aware of the problem and making them accountable.  If your lawn is mowed by professional landscapers, talk to them about protecting your trees and shrubs.  If you notice damage is being done to your trees, hold them accountable for the damage they have done to your trees and shrubs.   


Protect your trees and shrubs from lawn maintenance equipment by removing the grass and placing a 3-4 inch layer of mulch around your trees and shrubs.   You can also place a protective plastic tree guard on the trunks that will absorb the impact of string trimmers.  Trunk guards and other protective devices will only work for so long, especially if area around the trunk is not respected.  


For information about proper mulching or the impact of tree wounds, visit  or contact your local Penn State Extension Office.

Vincent Cotrone is an Urban Forester and  ISA Certified Arborist, Penn State Extension