My LEAST favorite yard and garden tool is the weed wacker. They cause much damage in the landscape when not properly used.I have seen many wonderful trees and shrubs killed a slow death by repeated weed wacker injury to the bark at base level. Often times, the operator of the weed wacker is only focused on cutting the grass to be even with the lawn and not about the bark of the tree. Granted it is sometimes difficult to see the exact stretch of the string circling around and where it is hitting, but the damage inflicted is easily visible and long-lasting.
Just under the outer bark of trees and shrubs is the vascular system. This is like veins carrying the nutrients and water from the roots up to all portions of the tree. Making a cut in the bark disconnects the transport, effectively creating a roadblock at the cut area. If a cut is made completely around the circumference of the trunk, the tree will die by the next year. No water will be carried up to the branches and leaves. Making small cuts that can and do happen with weed wackers leads to a slowly dyeing tree. The ‘veins’ do not reconnect.
Prevention of weed wacker damage begins with physical barriers to keep the wacker away from the bark. Mulch is good solution. Remove all the grass and plants growing around the tree and replace with a two to three-inch layer of mulch. You decide how wide to make the circle of mulch, however at least twelve inches will be sure to provide protection. When applying mulch, it should not touch the bark. Mulch burying the bark will leave keep the bark moist and rot the bark, causing much the same results as weed wacker injury.