Bark torn off by a mower or trimmer can kill a young tree. Tree trunk damage repair starts with sizing up the wound. For most wounds, the fix is simple: trim torn bark back to firm edges, leave the wound open, and skip the paint.
We mow lawns and don’t do tree work, but one of our own mowers has hit a tree. Part of what we did that day isn’t how arborists would handle it now.
What to do when a mower or trimmer hits a tree:
Check how far around the trunk the bark is torn or gone. If it’s less than a quarter of the way around, the tree will probably recover. When bark comes off all the way around, we call that girdling. Everything above a girdled spot eventually dies.
Young trees take it hardest. Their bark is smooth and thin, and the layer that carries water and nutrients sits right under it. Trimmer line that knocks weeds down to the dirt can do the same to that bark.
Repeat hits matter too. Every new nick slows the healing, so a trunk that gets clipped every week may never close.
The rear tire of one of our mowers clipped the base of a young tree and tore off a 3-inch chunk of bark. The trees in that neighborhood were only a few years old, and a wound that size could have killed the tree.
We kept the piece that came off. We fit it back in like a puzzle piece. Then we wrapped it in duct tape to keep insects and disease out. The plan was 3 to 6 months under wrap while it healed.
Putting the bark back fast was the right instinct. That’s the only time it has a chance, and only while the underside is still moist. Even then, it usually doesn’t take.
If the piece is dry, cracked, or lost in the grass, skip this and go straight to cleanup. Otherwise, press it back into its exact spot and tie it on with soft cloth strips.
We wouldn’t use duct tape today. It fixes plenty around the house, but on a tree it can tear healthy bark when you pull it off. Any wrap left on too long can cut into a growing trunk, so check it often and take it off before it gets tight.
Usually the bark is too shredded to save. With a sharp, clean knife or pruners, cut away the loose, ragged bark until the edges are firm and tight to the wood. Cut only what’s loose. Taking off healthy bark makes the wound bigger.
Don’t reshape the wound, either. Older advice said to trace it into a neat oval with pointed ends. That only makes the wound larger and doesn’t help sap move around it.
Leave the wound open to the air. Wound paint, tar, and spray sealers don’t stop decay, and they can hold moisture against the wood. Paint makes a wound look treated, and that’s about all it does.
For an older wound, pull off only the dry, loose bark. If you can see a ridge of new wood rolling in from the edges, leave it alone. That ridge is the tree closing the wound.
A well-watered tree seals a wound faster, and Northern Nevada summers are dry. During the growing season, water to a depth of 18 inches, out to the edge of the canopy. Move a slow-running hose around under the branches so the water soaks in instead of running off.
Watch the wound over the next few years. Each summer, the ridge of new wood around it should creep a little farther in.
For anything past a small wound, find a certified arborist. An arborist can tell you whether the tree will make it and whether it’s safe to keep. Call one especially if:
Spread a ring of wood chip mulch 2 to 4 inches deep and a foot or more out from the trunk. Then nobody mows or trims against the bark. Pull the mulch back so it doesn’t touch the trunk. A bag of wood chips costs less than a new tree.
Clearing grass from the base helps too. It’s the same trick we suggest to protect sprinkler heads from the mower: what’s easy to see is easy to go around. If grass has to grow near the trunk, finish the last few inches with hand clippers.
Most do. A wound on one side usually closes over in time, as long as the mower stays away. A girdled trunk is the exception, and that tree rarely recovers.
No. Sealers don’t keep rot out and can trap moisture against the wood. Fresh air does more for the wound than anything you can brush on.
A small wound can close in a few months to a season. A big one can take years, and some never close completely. Inside, the tree works to wall off the damage the whole time.
Cory’s Lawn Service handles weekly lawn mowing in Reno and Sparks, with edging, string trimming, and a complete blow-off on every visit. Before the first mow, our crew lead walks the property and writes down what’s there. When we spot something that needs attention, we follow up with you.
