By Jeff Burbrink
Ag & Natural Resources Extension Educator, Purdue Extension LaGrange County
LAGRANGE — It’s lawn mowing season, and along with that come requests for advice about tree roots that have made the mowing a more difficult task. Roots in an area you mow can make for a bumpy ride, and a tripping hazard for human feet, and result in hazards to both humans and the tree. What is a person to do?
First, lets review why this happens. Contrary to popular thinking, most tree roots grow within 4-10 inches of the soil surface, not straight down in a mirror image of the above ground portion of the tree. Just as a healthy tree trunk grows and gets larger, so do healthy roots. Over time, some of the more successful roots may break through the soil surface due to normal growth. Other roots might become visible due to soil erosion around the tree.
Some tree species are more prone to produce surface roots than others. Trees like maples, poplar, cherry and willow are among the trees I hear the most complaints about. All these species evolved to have shallow roots that can tolerate wet soils. As you consider planting trees in your lawn, consider the characteristics of these trees and whether the location is a good place to battle with surface roots.
There are only three or four good options to consider when a tree has surface roots, short of tolerating the situation or removing the entire tree. The offensive roots can be pruned out, especially when they are breaking up sidewalks and pavement. Be sure to cut them cleanly with a sharp saw to minimize the wound.
This root pruning approach has major flaws. First, any wound you create is an entry wound for bacteria and fungi to infect the tree, setting in motion a potential for rot that might not become visible for a decade. Another issue: just like above ground branches, tree roots are often stimulated to send out more shoots after pruning. Two or three years later, you often have a noticeable increase in surface roots after a pruning cut.
Another approach that homeowners often attempt is adding soil to cover of the roots, usually an inch or two in depth. If you are considering this strategy, please remember, these surface roots are the most successful roots on the tree, and it will not be long until the roots have pushed their way through the newly applied topsoil. You can only apply topsoil once or twice in a lifetime, and then the soil around the tree is going to be elevated dramatically, and it might look bad, much less have the potential to limit the trees’ ability to take oxygen in from its roots (yes, that is important too!).
Perhaps the best and most permanent solution, short of removing that tree, is to replace the turf with ground cover plants or mulch the area with an organic material like shredded or chipped hardwood bark. If you chose the groundcover option, select plants that have moderate to better shade tolerance. The area under trees can get quite dry in the summer months, so selecting plants that are drought tolerant can be a plus, too.
