String trimmers can cause significant damage to young trees or those with thin bark. (Photo by Dan Gill.)

For Release On Or After 08/02/13

You can do many things to protect your plants from damage. Here are a few to consider.

Avoid mower and string trimmer damage

Mowers and string trimmers that use a monofilament line for cutting weeds and grass can be damaging to young trees and trees with thin bark. If the line is allowed to hit the trunk, it will remove part of the bark with each contact. 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. So damage that occurs when mowers or string trimmers remove patches of bark interferes with the tree’s ability to send food to its roots. This can cause the tree to be stunted. Remove a complete ring of bark, and you may cut off food to the roots altogether, leading to plant death.

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 decay.

To prevent these problems, do not allow grass to grow close to the base of young trees for the first three to five years after planting. Keep an area grass-free at least a foot out from the trunk. A mulch 2 or 3 inches thick spread evenly over the area – but pulled back slightly from the trunk – will help a lot. Any stray weeds can be pulled or killed with a quick spray of the herbicide glyphosate.

Shrubs are generally planted in beds, so they are less at risk. But I have seen this problem occasionally when ground covers, such as Asiatic jasmine, are trimmed away from the base of shrubs with string trimmers.

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 and shrubs.

Don’t damage roots

Trees are also vulnerable to root damage from construction and filling. If you plan on doing construction – whether building a new home, adding on to an existing one or even putting in a patio or repairing driveways or sidewalks – tree roots will likely be an issue.

Tree roots extend well beyond the reach of the branches, and the majority of the feeder roots – those that absorb water and minerals from the soil – are located in the upper 8 to 12 inches of the soil. This makes them much more vulnerable to damage than most people appreciate. If you will be doing construction or filling around valuable existing trees, consider consulting a licensed arborist before the work is done to make sure the trees are damaged as little as possible.

Be careful with pesticides and fertilizers

Another way gardeners damage landscape plants is the improper use of pesticides and fertilizers. These products are useful and sometimes necessary to maintaining a healthy attractive landscape. But if misused, they can do more harm than good.

Pesticides commonly used in the landscape include insecticides to control bugs, fungicides to control diseases caused by fungus organisms and herbicides to control weeds. Landscape plants can be damaged by all three, but most damage occurs from insecticides because we use them more often than other pesticides. Herbicides also cause significant damage because they are, after all, designed to kill plants.

You can avoid damaging plants with pesticides by carefully reading and following label directions. I know the print can be very fine, but do as I do and get out the magnifying glass if you need to. Without complete information on how to use a product, your efforts may be wasted because applying any pesticide incorrectly does not control the pest and may even injure the plants you were trying to help.

Insecticides will list on their label which plants may be damaged by them and any temperature limitations. Some insecticides will damage plants if they’re applied during hot weather. And many insecticides will burn or damage plants if you mix them too strong. So, you can see how important it is to know of these potential problems and avoid them by following label directions.

Because herbicides are designed to kill plants, we must be particularly careful when using them around desirable ornamentals. Again, read the label to make sure the herbicide will do the job you need it to do and to understand how to use it properly.

Many people also damage plants with fertilizers or plant food. Gardeners often think if a little is good, more is even better. But fertilizers should never be applied stronger than label recommendations. You may apply less than is recommended, but mixing fertilizer stronger or applying more than the label recommends can lead to serious plant damage.

Rick Bogren