Lawn Mower Damage

Have you beaten your tree lately? Maybe you ran into it somewhere. If you did accidentally, you are destroying the vitality of your tree more than you know. Most people do not understand that injury and infection started by lawnmower wounds can often be the most serious threat to tree health.

Lawnmowers cause the most severe injury during periods when tree bark is most likely to "slip" which is in early spring during leaf emergence and in early fall during leaf drop. If the bark slips, a large wound is produced from even minor injuries.

Most tree injuries occur when mower operators attempt to closely trim grass around trunks with a push or riding mower. You can prevent this scenario by removing the turf around the tree, or by hand trimming.

The site of injury is usually the root buttress, since it flares out from the trunk and gets in the path of the mower. However, injury is also common anywhere from the roots up to several feet above the ground.

Although large wounds are most serious, repeated small wounds can also add up to trouble.

Wounds from lawnmowers are serious enough by themselves, but the wounded tree must also protect itself from pathogens that invade the wound. These micro-organisms can often attack the injured bark and invade the adjacent healthy tissues, greatly enlarging the affected area. Sometimes, trees can be completely girdled from microbial attack following lawnmower wounds.

Decay fungi also become active on the wound surface and structural deterioration of the woody tissues beneath the wound will often occur. Many wounded trees that are not girdled may eventually break off at the stem or root collar due to internal decay.

Bark can often be successfully reattached to trees if the wounds are treated within a few hours after injury occurs. Torn bark should be reattached as close as possible to its exact pre-injury position and held in place by a few small tacks or staples.

If several days or weeks have passed since the injury, torn or loose bark should be cut away and the edges of the wound should be traced using a hand tool such as a pruning knife.

Pruning tools should be sterilized with a weak bleach solution before working each tree. There is no need to cut additional tissue around the wound to achieve a certain shape. Avoid making deep scribes or any vertical sharp points that would serve as additional sites for bark die-back or starting points for bark cracks.

Older injuries with callus development all around the wound are best left alone. If there is any dead bark old wounds, it is advisable to trace the area back to live bark. Application of wound dressing for cosmetic purposes is optional.

Spreading organic materials such as leaves, grass clippings or straw under and around trees will effectively control grass and weeds and provide an attractive appearance around the base of the tree.

Not only will mulching with organic materials prevent grass competition, it will also conserve moisture for use by the tree roots and stabilize soil temperatures (since roots don't like extremely hot or cold soils). Young trees should be surrounded with at least 3 feet of a thick mulch (3 to 4 inches deep) that is maintained throughout the growing season.

If trees are closely surrounded by tenacious grasses such as bermuda, the turf should be removed or killed. The safest grass killer that can be used near young trees is glyphosate which is sold as Roundup, Kleenup, Weed Away, and Weed and Grass Killer. This herbicide will totally eliminate grasses, roots and all, yet is inactivated upon soil contact. Be sure to use a piece of wood, cardboard, etc., as a shield during spraying to prevent spray droplets from touching the trunks or foliage of your desirable plants.

Grass and/or weeds should be removed from around tree trunks and beneath trees if maximum growth is expected. Grass and/or weeds compete for the same nutrients and water that the tree needs. During the summer when rainfall is low and less than adequate watering occurs, the competition for water imposed by weeds or grass turf can substantially reduce tree growth. When competition from grass is eliminated, tree roots are more evenly distributed, root numbers are higher and they utilize a larger volume of soil. Effective utilization of soil by a larger root system will mean that the fertilizer you have added will be utilized more fully.

Liberal watering can offset the retarding effect of grass. Obviously, if the competition with grass for water, which the tree needs during dry periods, can be overcome by extra watering, the tree will have a more optimum growing condition. Your trees need a deep, thorough soaking once a week in the growing season either from natural rainfall or from supplemental irrigation. Whenever you must irrigate, be thorough and allow the water to deeply penetrate. The best way to water large trees is to let water slowly flow onto an area under the drip-line of the trees for several hours. Remember that watering which is adequate for lawn grasses growing under trees, IS NOT adequate enough to provide for the needs of an actively growing fruit tree!

The problem of lawnmower injury is not a tree problem but a people problem. It is a classic case of communication breakdown. The solution is to educate lawnmower operators about how serious these wounds can become and also to protect trees from careless grass trimmers such as weed-eater maniacs and lawnmower jockeys who enjoy using tree trunks as crash sites. A mulched area around the tree trunk can provide protection from these types of tree-damaging behavior.

So if you want fast growing trees don't abuse them with weed-eaters and lawnmowers! Spread some organic material around their base and keep weeds and grass at bay.