Gardening With Allen: Protect tree bark from damageee

I use my line trimmer around my lawn edges, trees and deck. My wife read that trimmers can damage trees. Doesn’t the bark protect trees from damage?

Line trimmers are a very handy tool for edging and trimming lawns. Older trees with thick bark will withstand trimmer damage for a long time but trees younger than 10 years can be damaged in a much shorter time.

The inner bark contains tubes that transfer food made by the leaves to the roots. Every time the grass is trimmed around a tree, little nicks are made in the bark. It does not take long for those nicks to cut through the area where the food transporting tubes are located. Damage to these tube-like cells reduces the amount of food which reaches the root system. A reduction in the root system reduces the tree’s growth rate. A small reduction may not be noticeable. Eventually new branches become shorter and even leaf size is dwarfed. Once all the tubes become cut all the way around the tree trunk, the tree will die.

Even without trimmer damage, letting grass or weeds grow right up to the tree trunk can reduce growth by 50 percent.

I once planted an apple tree near my back fence. At about the same time, my neighbor planted an apple tree of similar size on his side of the fence. He jokingly said, “Your tree will probably grow much faster than mine because you have a green thumb.” I was careful to keep a 6-foot circle around my tree with no grass or weed growth. He did not pay much attention to what was growing under his tree. After just two years my tree was twice the size of his tree. Grass has many fibrous roots that are very effective in competing for nutrients. Grass also produces a substance that inhibits growth of other plants growing nearby. A young tree’s growth rate can be reduced by almost half when grass is allowed to grow up to the trunk. Maintaining a circle of mulched soil around young trees will not only protect them from damage, but reduce competition for water and nutrients, resulting in faster growth.

A 1-inch layer of mulch will reduce sprouting of annual weeds by about 90 percent. If you have let grass grow under trees you can spray with an herbicide such a Roundup and then cover the area with a mulch such as bark dust. Plastic or metal edging will keep the grass from growing back into the circle.

You can achieve 100 percent weed control by covering the area with fabric mulch. In most cases fabric mulch is covered with granular mulch for appearance.

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