By Diana Alfuth, Horticulture Educator
Those big, beautiful shade trees in our yards often come with the problem of surface roots—roots that are visible on the lawn surface. These surface roots not only affect the appearance of the lawn, but they can make mowing difficult and create tripping hazards. Almost any large, mature tree can develop surface roots, but species like poplar, willow and silver maple tend to be most likely to do so.
The majority of a tree’s roots grow horizontally in the top 4-15 inches of the soil. They do this because they need oxygen, which permeates from the surface of the soil. Heavy, poorly-drained or compacted soil encourages shallower root growth. Each year a tree’s roots get thicker, just like the trunk does, and eventually they can break the surface and be visible in the lawn. Erosion of soil over a root system is another cause of surface roots.
Damaging these roots, such as by hitting them with a lawn mower or trying to prune them away can seriously affect the health of the tree. To protect the tree’s roots, make mowing easier and reduce tripping hazards, you can apply a shallow layer of topsoil around and over the exposed roots. Apply just enough to cover the roots by about a half inch. Applying too much soil over the roots of a tree can suffocate them and cause tree damage or death. After a few years, since roots get thicker each year, they may again break the surface, and you’ll have to apply another thin layer of soil to cover them.
Another option for areas with surface tree roots is to eliminate the grass and cover the area with mulch such as shredded wood. You can also plant the area with a groundcover or perennials in a mulched bed. Just be sure you don’t damage the tree’s roots when planting, and don’t use a rototiller in the area. Instead, hand dig small planting pockets in between the tree’s roots.