Microorganisms that might decompose thatch are unable to survive or perform well in our poorly aerated clay soils. Without the microorganisms to break it down, thatch accumulates. To determine if thatch is present, cut out a pie-shaped section of turf and soil. Look for a brown, spongy layer between the soil and grass. If it is a half-inch or less, don't be concerned.
Some thatch is needed for insulation and resiliency.
But if it exceeds a half-inch, then it should be managed by core aeration . This process pulls plugs of soil out, which changes the physical composition of the thatch. Eventually, air and water movement into the soil increases, improving root development. At least one treatment per year is recommended. Sloped areas also are prone to browning.