Hort Q&A: Weeding around trees

Carla Smith, horticulture educator
Pottawatomie County Extension Service
Tree guard

We have some newly planted trees this year. Do you have recommendations for weeding around them?

One of the leading causes of death to trees in the landscape is what we refer to as weed-eater or lawnmower “blight.” This is usually a result of someone trying to get too close to the base of the tree when controlling grasses and weeds. Constant use of weed-eaters around the base of trees wears down the bark and eventually cuts into the cambium layer girdling the tree and cutting it off to water and nutrients. Lawn mowers often take big chunks out of the trunk of the tree with similar results. The other problem is both wounds open the tree up for attack from insects and/or diseases.

To avoid this problem a weed and grass free area should be maintained around the base of the tree. For young trees a 4- to 6-foot diameter circle will work. Mulch can be placed 1 to 2 inches thick in this area to help keep weeds and grass out and at the same time moderate soil temperatures and soil moisture. Be sure to keep the mulch a few inches away from the trunk. Piling mulch several inches up the trunk is often referred to as a “mulch volcano” and can also have detrimental effects. Occasionally weeds and grasses that creep into the mulched area may need to be sprayed with an herbicide. Herbicides with glyphosate as the active ingredient work quite well. Be sure to read and follow label directions.

Another option for small trees is to put trunk guards or protective wraps made of flexible plastic. In some cases, tree stakes act as a barrier from mechanical injury.

For larger, more established trees, a mulched area or even a bare area near the trunk will help keep lawnmowers and weed-eaters away. Or consider planting groundcovers or perennials for a more aesthetical appeal.

In any event, avoid injury to the trunks of your trees at all costs. While many trees can recover from an occasional, small wound, repeated damage weakens the tree sending it into a declining spiral and eventually death.