Can a Weed Eater Really Kill a Tree?

This could be my shortest post ever: Yes! Generically called weed eaters, weed wackers, trimmer/edgers, these are the gas, battery or plug-in electric tools used to cut down weeds or grass next to trees, buildings, fence lines or to create an edge along a sidewalk or driveway.

Innocuously called string trimmer line, many people don’t realize the damage caused by the fast spinning, plastic line. After all, trees have protective bark. But depending on the species that bark is not always very thick. The repetitive injuries, often on a weekly basis during the growing season, can eat into even the thicker bark of trees. And you cannot help but hit the tree if the grass or weeds are growing up right against the trunk. You may not see the damage but it is happening.

Weed eaters aren’t the only culprits in the lawn care line up that cause damage to trees. Let’s take a look at other lawn care practices.

The lawn mower
To the person mowing the lawn, the tree is an object specifically planted to, at the least, be an annoying object to avoid and, at worst, be actively out to create grievous bodily harm. I don’t know if the physical act of running the mower into the tree, on purpose mind you, is some kind of subliminal payback but it is strongly not recommended due to the damage it can cause the tree.

A case in point: We were called out to remove a tree with severe dieback on one side of the tree. The people asked if we had any idea what caused the decline. After looking at the base of the tree, we asked about lawn care practices. Checking the base cut after the tree had been taken down, there was a distinct time of injury with limited growth. I counted growth rings on the live portion to see when the injury first appeared. When I told the homeowner, it looked like the damage had started approximately 12+ years ago, he stated that was about when he got his riding lawn mower and the flange from the mower always hit the tree on that side when he mowed.

In addition, some tree species have shallow root systems, staying close to the surface. This can be exacerbated by a watering regimen that applies a little bit of water frequently rather than the preferred longer sets less often. These roots will inevitably be clipped by the lawn mower creating an open wound on the tree root for pathogen entry and annoying the heck out of the lawn care provider. This issue can be avoided by better plant selection and better watering protocol.

Herbicides
Many people like to control broadleaf weeds in their lawns. And I understand that. However, many trees, and shrubs for that matter, are broadleaf species. Just because they are bigger than dandelions does not mean they are not susceptible to the herbicides applied to control annoying weeds. Many of these products are available to homeowners as well as professionals. And as such, I believe people tend to think if it is “over-the-counter”, it can’t be too lethal. In fact, some products can kill trees, susceptibility varying depending on the species. Unfortunately, please do not assume a professional pesticide applicator is fully aware of the potential for damaging trees and shrubs on your property. We see chronic damage to many shrubs and trees by both the homeowner and the professional.

    
Damage can be subtle and potentially lethal or dramatic and definitively lethal.

With any of these factors, you may think it doesn’t matter because the tree didn’t die and, in fact recovered with no visible signs of lasting damage. However, stress has been applied and this is often a recurring event. Stress builds up in a tree. It doesn’t “go away”. A stressed tree is more susceptible to other issues such as insect deprivation or pathogens. We try to avoid creating unnecessary stress whenever we can.