Line Trimmers Can Damage Trees

One of the more popular uses of line trimmers is to trim grass and weeds growing around trees. An occasional use around a well established tree probably does little damage. However, weekly use around trees, especially young ones, is devastating. Every time the line hits the bark of a tree, a little outer bark is removed. As fast as line trimmers rotate, that may be a hundred times in one trimming. After 10 or 20 trimmings, there may be little or no bark left.

The inner bark of a tree contains the tubes which carry food manufactured by the leaves down to the roots. If some of these tubes are damaged, less food reaches the roots. Slowing root growth means the tree can support fewer leaves. This reduces the growth rate and can actually reduce tree size as leaves are shed to balance top growth with root capacity. Once all the conducting tubes are cut, no more food reaches the roots and they begin to die. A slow, painful death of the leaves and branches follows.

The simplest way to avoid tree damage is to create a circle of mulched soil around the base of every tree which is free from grass and weeds. This should be a minimum 3 foot diameter circle for individual trees. The size of the circle should be increased with tree growth. Groups of trees and shrubs can have irregularly shaped beds around them.

Bark dust mulch not only improves the appearance of shrub and tree beds, but reduces water loss and weed sprouting. The most common bark is from Douglas Fir trees. It is reddish brown in color, but ages to a darker brown. Hemlock bark is a darker brown color and ages to almost black. They are of equal effect in reducing water evaporation loss from the soil. They also work equally well in reducing weed seed sprouting by preventing light from reaching weed seeds in the soil. A gradual buildup of mulch over a period of years will allow plant roots to adjust by growing into the mulch. Adding several inches at one time, especially near tree trunks, can damage plants.


Allen Wilson

Allen has been writing about gardening for over 30 years. He is a retired professor of Horticulture.

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