By Heather N. Kolich, County Extension Coordinator, UGA Extension Forsyth County, May 2022
In the past few weeks, several county residents have contacted the Extension office for advice about managing troublesome tree roots in their yards and subdivisions. Trees provide shade, beauty, and character to our landscapes. Sometimes, however, the roots below diminish enjoyment of the beauty above. When trees lift their roots to the soil surface, they create tripping hazards and mowing issues. In urban settings, tree roots can damage
sidewalks, driveways, foundations, and clog sewage systems.
What causes surface roots?
Active tree root growth occurs horizontally from the tree trunk at a depth of 18 or fewer inches. Urban and suburban soils are usually not ideal and suffer further from compaction. When soil is compacted, all the little pockets or pores that hold oxygen and moisture are squished flat. Construction, parking or driving on soil, mowing, and even foot traffic can cause soil compaction. Deprived of necessary oxygen at deeper soil layers, roots grow closer to the soil surface. As the structural roots near the tree grow in thickness, they can emerge above the soil surface. Erosion can also expose roots.
Is it OK to cut surface roots?
The short answer is, “No.” Roots serve two critical functions in trees: stabilization and nutrient storage and transfer. Lateral roots are thick, woody roots that spread outward from all around the tree trunk. They provide structural support to keep the tree from toppling over. These structural roots may extend 3-6 feet from the trunk before tapering to flexible roots that grow for a span seeking moisture. When they find a moist spot, these roots fan out into hundreds of thin roots that absorb water and nutrients from the soil. The root system transfers moisture and nutrients upward through the tree to nurture the shoot system of branches, stems, leaves, flowers, and fruits. Tree roots that grow into the lawn make mowing difficult, and the mower causes root damage when it strips bark and cuts into the root. As tempting as it may be to simply cut
these roots back to the decorative ring or mulch island around the trunk, doing so can cause permanent damage that leads to dropped limbs and tree death a few years down the road, or to destabilization from loss of structural roots. Trees that are not supported by roots on every side may topple suddenly in a storm or strong winds. One rule of thumb suggests that diameter of the root zone circle should be 1 to 1.5 times the height of the tree.
Can I rebury the roots in soil?
Again, the answer is, “No.” A light covering of soil is likely to wash away fairly quickly, and a deep covering could suffocate the roots and lead to tree death.
What’s the best way to deal with surface roots?
The simplest and healthiest way to manage surface roots is to apply mulch around the tree (but not touching the trunk) out to the dripline of the tree or around the area of critical root zone. The layer of mulch should be 3-4 inches in depth. This action has several beneficial results:
- Mulch suppresses weed growth around the tree, eliminating competition from other plants for water and nutrients
- Mulch eliminates the need to mow, thus protecting roots from damage from mower blades
- As the compost breaks down, it recharges the soil with organic matter
- Over time, the addition of organic matter relieves soil compaction, improves water infiltration, and improves the structure of the soil
Trees are important to our landscapes, and healthy roots are important to sustaining those trees. Maintaining a 3-4 inch layer of mulch over surface roots is the best solution for both tree and human health.