Archive for Wednesday, August 27, 2014

Garden Variety: The root of the problem

August 27, 2014


When tree roots push above the soil surface, they can make it difficult to maintain a lawn or other groundcover. But chopping them out, piling mounds of soil over them, or shaving off the tops of the roots can impair the livelihood of the tree. To get trees and lawns (or other plants) to coexist, the best solution is to understand what is causing the problem in the first place.

Many people know that trees have about as many roots as they do branches. When I first learned this, I had a picture in my head of a tree’s root system as a mirror image of the top, upside-down and underground. Standing beneath a giant old maple in my parents’ yard made me question my own theory, though, because I could see large, old roots running horizontally at a great distance out from the trunk.

Turns out, tree roots and tree tops are close in ratio of mass but very different in growth habit. Throw that picture of the upside-down tree and a giant taproot out of your memory. Instead, picture a wine glass sitting on a turkey platter, something I heard from a tree scientist many years ago. The wine glass represents the tree, and the turkey platter is representative of the tree’s root system.

Tree roots are located in the surface layers of the soil because that is where the water, air, nutrients and beneficial microorganisms all live. Also, the soil is more likely to be penetrable here. If you have ever dug a deep hole into subsoil, you know that even a shovel has a hard time pushing through in some places. Actual depth depends a lot on individual location, but most research indicates that the majority of tree roots are in the top 36 inches of soil.

Why do roots push above the soil surface? Most often, they are in search for air and water. The roots of turfgrass and other groundcovers can provide heavy competition. Soil also becomes compacted over time as it shrinks and swells from moisture fluctuations, gets walked on, has mower wheels run over it, and reacts to the various activities that take place in yards. When soil is compacted, water and air movement are restricted in the soil.

Also, people often want to add soil in order to grow better grass, but grass has a hard time competing with tree roots as well as surviving in shade.

The solution: Determine if the issue is competition or compaction. If it is competition, consider getting rid of the grass or other groundcover in this area altogether. Use mulch to reduce soil moisture fluctuations, weeds and erosion. Or, use a drought-tolerant groundcover.

If the issue is compaction, core aerate the area and/or add compost to the soil in the area with as little disruption to tree roots as possible.

Cutting, shaving or burying tree roots will most likely lead to root decay and a shorter life for the tree.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation. She is the host of “The Garden Show” and has been a gardener since childhood. Send your gardening questions and feedback to Lawrence


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