Surface roots
Also called: root flare, buttress roots, exposed roots, tree roots above ground, root chasing, lateral roots
The large roots that flare from the base of a mature tree and run just under or above the lawn, sometimes for 10–20 feet. On a stump they add inches to the diameter and a root-chasing charge; left in place they decay over years — fine under grass, not under a slab.
Most of a tree’s root system is in the top 12–18 inches of soil, and the biggest roots — the structural ones that hold the tree up — run outward from the trunk at or near the surface. Maples, poplars, willows, elms, oaks and most trees in compacted or shallow soil push them above grade with age, which is why old lawn trees have a ring of ridges the mower hits. Where the roots meet the trunk is the root flare, and it’s where a stump is widest.
For grinding, two consequences. The stump’s diameter, measured at the soil line, includes the flare, so a tree that was 24 inches at chest height can be a 32-inch stump; that’s the per-inch price. And the roots themselves are a separate decision: standard grinding takes the stump 6–8 inches down within its footprint and trims the flare, but chasing the roots out along their length is priced by the hour or the foot ($50–$150 on a big tree) and slows a rental machine considerably. Under lawn, roots left in place decay over 5–10 years and the ground settles gently; under a future patio, slab, driveway or foundation they leave voids as they rot, and they should come out — by grinding deeper along their runs or by excavator.
On a living tree, surface roots aren’t a defect and shouldn’t be cut — removing a structural root can destabilize the tree and invite decay. Mulch over them or lift the mower instead. On a stump, the DIY guide covers chasing them with the same shallow sweeps as the stump.