What it looks like

Cut a small wedge out of the lawn with a trowel and look at the profile: thatch is the brown, fibrous, spongy layer between the green blades and the soil. Under half an inch is normal and even helpful. Past that, the lawn feels springy underfoot, water beads up or runs off instead of soaking in, the mower scalps on high spots, and the grass roots sit in the thatch instead of the soil, so it dries out and browns fast in summer.

Often mistaken for: Compacted soil, poor drainage, or a disease ring

When it shows up in the Triangle

Builds up over years rather than showing up overnight. It is most noticeable in summer, when a thatchy lawn dries out and scalps, and during spring green-up on bermuda and zoysia when old brown material is exposed.

Where you’ll see it

Mostly a bermuda and zoysia problem in the Triangle, since those grasses spread by stolons and rhizomes that pile up fast. Tall fescue is a bunch grass and rarely builds much thatch; what feels like thatch in fescue is more often compacted clay.

What you can do

Check the depth with a trowel wedge before doing anything; grass clippings do not cause thatch and can stay on the lawn
Core aerate: fescue in September or October, bermuda and zoysia in late spring or early summer when they are growing hard
Don't overfeed with nitrogen or overwater; both push the kind of growth that builds thatch
Mow at the right height and often enough that you never remove more than a third of the blade
For a thick layer on bermuda or zoysia, dethatching (vertical mowing) in late spring, followed by water and a light feeding, lets the lawn recover
Keep soil pH in range with a soil test; very acidic soil slows the microbes that break thatch down