A tree’s root system is much shallower than we often consider. Tree roots are more horizontally spreading than deep. In fact, most of a tree’s root system is contained in the upper 1 to 2 feet of soil, radiating out from the tree. Trees aren’t stupid; they spread their roots in the upper layers where the best topsoil is found, along with nutrients, oxygen and moisture. As trees age and roots thicken, it’s natural for parts of larger roots to extend above the surface. Some tree species are more inclined to develop surface roots, such as maples.
When parts of tree roots protrude above the lawn, it’s natural, and nothing is wrong; the tree is happy. We humans are the one’s that find it problematic as we try to conform the trees to our mowing habits. Surface roots make it difficult to keep lawngrass neatly trimmed because sometimes they’re large enough to snag the mower, and string trimmers can damage bark, harming the tree.
What not to do. Some sources have recommended cutting and removing the offending roots, indicating it might be safe to sever and remove one large root per year. This is NOT recommended by universities like Cornell and New Mexico State University. Cutting these large roots can diminish a tree’s natural support, making it more prone to uprooting in severe storms. Open wounds from severed roots could allow access by disease and rot organisms. Cutting roots has been shown to cause increased chance of corresponding branch death in the tree’s canopy. There isn’t adequate research to show what the long-term effects of removing large roots will be. Cutting roots has been done in some cases without short-term noticeable effects, but tree researchers are very leery of the long-term effects.
What to do. One of the following options can help.
- Perhaps do nothing, leaving them exposed. It’s natural, sort of Japanese garden style.
- Or fill around the roots with no more than 1 to 2 inches of good quality, non-heavy topsoil. Too deep will smother root systems and lead to tree decline.
- Or mulch with 2 inches of wood chips around the tree and between surface roots.