We receive calls all year long at the extension office about trees with large, exposed roots. Sometimes these roots will bust up sidewalks and driveways. The most common complaint from homeowners is that the surface roots interfere with the lawn. Exposed roots can cause uneven lumps in the turf, and they can also tear up a lawnmower with one pass.
Contrary to popular belief, the roots of most trees grow within the top 8-12 inches of soil, according to UGA's Randy Drinkard. Even trees like pines, which are often associated with "tap roots," will still have relatively shallow root systems that extend out past the drip line.
As with tree trunks, roots also expand in girth year to year. Over time, some of the older roots close to the soil surface will enlarge enough to become exposed. Natural soil erosion will also help make these roots more visible.
At this point, there is little that can be done to hide the roots without seriously damaging the tree. Root pruning is often attempted, but should only be used when roots far from the trunk are damaging concrete areas.
Some homeowners will try to spread new soil over the exposed roots and replant with grass seed. Given time, the tree roots will show through the new soil.
Another popular solution is to spread a thick layer of mulch over the surface roots. This method can cause damage to the tree by starving the roots of oxygen. It is never a good idea to attempt to change the soil level underneath established trees.
Unfortunately, there is no great solution for exposed roots. You may just have to accept that they are part of having mature trees. The best partial fix is to fill the area with groundcover plants that do not need to be mowed.
Exposed tree roots may be avoided by limiting tree planting in areas known to encourage shallow rooting. Soils that are compacted, waterlogged, or contain heavy clays promote shallow roots. These soils have small amounts of oxygen which encourages growth near the soil surface. If trees are already growing in compacted soils, aerating lawn areas around the trees can help reduce the compaction. Avoid planting trees in areas where standing water is observed after light rain showers.
Landscapes with irrigation systems are more prone to develop shallow-rooted trees. Most systems run too often. The best irrigation method is to water deeply and infrequently. This forces roots to grow more deeply to obtain water. In the absence of natural rainfall, one inch per week is the recommended irrigation rate.
Some trees are naturally prone to surface root development. These include poplars, maples, willows, sycamores, alders, elms, mulberrys, honeylocusts and figs. Avoid planting these tree species in or near turf areas.
Clark MacAllister is the Dawson County extension agent. For more information, call (706)265-2442.