Thatch can develop in lawns that have surface runners: zoysia, Bermuda and Kentucky bluegrass. It’s mostly hidden, on top of the soil but below the blades of grass, giving a soft and spongy spring to your step when you walk on it.
Roots, stems and runners become compressed to form thatch. Less than half an inch of it is good for the lawn; it provides a sort of mulch. But any more than that, and it is harmful. The grass roots have to make it through the thatch to reach the soil, and they don’t always make it that far, drying out and causing the grass to turn brown.
If thatch has built up in your Bermuda or zoysia lawn, June or July is the time to dethatch, when the lawn can bounce back and grow.
If thatch is more than 3/4 inch thick, rent a power rake and use it on the lawn. Set the blades just deep enough to pull out the thatch, or you can damage the lawn.
You may not eliminate a thatch problem with one treatment. And in some cases, you may want to use a sod cutter to remove the sod and start over with seed, sprigs or plugs.
If thatch is between 1/2 and 3/4 inch thick, core-aerate instead. Be sure the soil is neither too wet or too dry at the time; it should crumble fairly easily between your fingers. Go over the lawn enough times so that the aeration holes are about 2 inches apart.
To diminish thatch, be sure not to over-fertilize, and when you water, do so deeply and infrequently.
Fescue doesn’t get thatch, but bluegrass can develop it in very compacted clay soil that has been watered often and shallowly, extension agent Rebecca McMahon said.