With their large size and long lives, trees are among the most significant parts of our landscapes. Sometimes, especially in the case of older trees, it may almost seem like they are invulnerable.
But we need to remember that trees can be damaged by our actions. It’s important to understand how we may inadvertently hurt trees.
Save the bark, save the tree
Here’s a good example. A maintenance crew working on a homeowner’s landscape got too close to the trunk of a Japanese maple tree with a string trimmer and removed a lot of bark. The tree was looking sickly, and the owner asked me what to do for it. Unfortunately, the damage was done, and there was really nothing she could do to help the tree. If the damage was bad enough, the tree could die.
Park goers sit on a bench underneath one of the historic oak trees in City Park.
String trimmers and other equipment used for cutting down weeds and grass can be very damaging to young trees and trees that have relatively thin bark. If the line is allowed to hit the trunk, part of the bark will be removed with each contact of the line. If you are not careful, you might even remove an entire ring of bark all the way around the trunk, girdling the tree. Mowers pushed hard or dragged around the base of young trees can be almost as damaging.
The part of a tree’s circulatory system that carries food manufactured by the leaves to the roots (which can make no food for themselves) lies just under the bark. Damage that occurs when mowers or string trimmers remove patches of bark interferes with the tree’s ability to feed its roots.
The roots may begin to starve and function poorly — and this leads to a stunted, unhealthy tree. If you remove a complete ring of bark, you may cut off food to the roots altogether. The roots starve, leading to the death of the tree.
Many sickly trees that have been planted for a few years but don’t grow well have been damaged in this way. Look at the base of their trunks and you will often see scars and callus growth from repeated injury done to the base of the tree.
In addition to interfering with food movement, the open wounds created by mowers and trimmers can provide entry points for disease organisms that can cause infections and decay.
To prevent these problems, do not allow grass to grow close to the base of young trees for at least the first three to five years after planting. And for thin-barked trees like Japanese maples and crape myrtles, you must prevent damage their whole lives.
Keep an area at least a foot out from the trunk grass free — and farther out is even better. Keep the area mulched to prevent grass and weeds from growing. Any stray weeds can be killed with a quick spray of the appropriate herbicide, if necessary (do not allow the herbicide to contact the trunk of the tree).
Not only does this protect trees from string trimmers, but keeping the area mulched and free from grass encourages faster growth. Grass roots compete with the roots of the young tree for water and minerals. And grass roots release chemicals into the soil that can inhibit tree-root growth. Research indicates trees with grass removed from around their trunks and mulched grew twice as fast as other trees.
Tree guards placed around the lower part of the trunk of young trees can also be used to prevent this type of damage.
Shrubs are generally planted in beds so are less at risk. But problems occasionally arise when ground covers, such as Asiatic jasmine, are trimmed away from the base of shrubs with string trimmers, or when large shrubs like camellias are grown individually in lawn areas.
Whether you maintain your landscape yourself or pay someone to do it for you, don’t let this kind of needless damage happen to your trees.
Mulch properly
Speaking of mulching around trees, it must be done properly. Mulch should never be piled up in a mound or cone around the base of the trunk — a practice that has been dubbed “volcano mulching.” Piling the mulch deeply around the base of the trunk exposes the trunk to dark, moist conditions. The bark was never meant to protect the tree from this kind of environment, and decay organisms can take advantage and invade the trunk.
When mulching trees, the mulch should be spread out in a flat disk 2 to 4 inches deep and pulled back slightly from the trunk. As the mulch thins out and decays, add more mulch as necessary.
Protecting older trees
A variety of activities can damage the roots of existing trees. The majority of a tree’s root system that absorbs the water and minerals a tree needs are in the upper 12 inches of soil. Many people do not realize the roots are so shallow.
Filling deeper than 2 inches over the roots can prevent the roots from getting the oxygen they need, suffocating them and leading to the decline or even death of a tree.
Digging trenches in the area covered by the canopy or near the trunk can sever major parts of a tree’s root system, again leading to decline. Construction of home additions and installing roads, driveways and sidewalks can also damage roots.
Whenever possible, keep construction activities as far away from mature trees as possible. Create a protected zone around the tree reaching out as far as the branches to ensure a tree is not damaged by the construction.
