Tree and yard owners are often faced with the problem of a tree's exposed surface roots. Tree roots that grow on the surface are difficult to mow or walk over and can affect the growth and health of nearby grass and ground covers. The usual response to remedy the situation is either to cut the roots or add fill soil over the roots and then replanting grass or ground cover.
However, cutting out surface tree roots is not advisable as tree roots offer structural support and provide a nutrient flow that supports growth and vigor. When damaged, tree roots attract pests and pathogens. Trees that experience root removal or serious root damage can express top canopy death on the side the roots were harmed. Removing roots can also introduce rot into the root, the base, and the trunk of your tree.
Adding supplemental soil to cover roots can also harm your tree. You can, however, add an additional cover like mulch over roots to smooth out the surface of the landscape. Adding extra dirt, on the other hand, can reduce the concentration of soil oxygen needed for roots to survive, and trees may begin to show symptoms immediately or decline over time upon covering them.
Proper Treatments for Surface Roots
Ultimately, the best advice for gardening or landscaping in a yard that has surface tree roots is to leave them alone and incorporate them into your designs.
Don't grow your garden or introduce small ornamentals near a tree's surface root system (its life-support system, essentially) as introduced extra vegetative competition may or may not survive against these large trees. Having plants that heavily compete for nutrients and light is never good within the tree's critical root zone-the tree may not suffer but the cover plant will lose vigor, probably struggle to thrive, and will cost you the price of the plant plus the planting time.
A better way to deal with surface roots is to cut a bed around the offending root system and cover with coarse mulch, making sure to not add more than an inch of extra soil. Trying to establish even a patch of tolerant grass or ground cover among the surface roots can often be difficult, and it might actually be impossible to do because of natural tree root toxins produced by certain tree species.
Symptoms of Tree Root Damage and Fill Injury
In addition to the root injury itself, other visible symptoms of injury may include small, off-color leaves, premature fall color, suckering along the main trunk, dead twigs throughout the canopy of the tree, or even death of large branches.
The types of tree injury will vary by tree species, tree age, the health of the tree, root depth, type of fill and drainage. Trees that are usually severely injured by additional fill include sugar maple, beech, dogwood, and many oaks, pines, and spruces.
Birch and hemlock seem less affected by root fill damage than other species, but elms, willow, London plane tree, pin oak, and locust seem to be the least affected. Older trees and those in a weakened state are more likely to be injured than younger, more vigorous trees when it comes to soil fill damage.