When Thatch is a Problem

In Kentucky, we often struggle with quality lawns for many reasons. Cool season grasses do not perform well with a hot summer and warm season grasses are not as pleasing during the cooler months when they are dormant. Good overall maintenance practices play a critical part in our success. Aerifying and dethatching could be important to your specific lawn needs.


Thatch is a tightly intermingled organic layer of dead and living shoots, stems, and roots that develop right at the soil surface. This layer develops when organic matter is produced more quickly than it can break down. Most of the time, thatch build up is not a problem with low maintenance lawns and more of a problem with higher maintenance lawns. It is important to note that some thatch is important as it helps moderate soil temperature. Typically, we like to see less than ½ inch of thatch.

Managing thatch build up is important. Earthworms help out with this process as they help break down the organic matter. The more earthworms present, the less problems you should have with thatch build up.

Mechanical thatch removal is an option. Many local rental yards offer a “de-thatcher” for rental. These machines have vertical blades that cut through the thatch layer bringing up the dead material to the surface. Often, depending on the amount of thatch present, it will be necessary to cover your lawn in two or three directions to sufficiently remove thatch. Remember that cool season grasses such as fescue and KY bluegrass are stressed during the warm months, so dethatching should be performed in the spring or late fall.

Aerification is another option for controlling thatch with the added benefit of reducing compaction. This method involves removing cores 2-3 inches deep from the lawn. The cores are deposited on top of the grass and naturally break up over a week or two. Thatch reduction occurs because the extracted soil mixes with the dead organic matter speeding up the decomposition.

Core aerifiers are often available from local rental yards, but sometimes more difficult to find than a de-thatcher. Consider contracting this service with local lawn care companies. As with de-thatching, aerifiying in two or three directions is preferred. Most aerifying equipment will allow several different size tines. Use the largest tine available; most often ¾” or 1″ will be standard.

De-thatching or aerifying your lawn is just one more practice that will increase the health of your lawn. Good fertility, mowing regularly and at the correct height, and keeping a sharp blade on your mower will also help. Following best practices with your lawn before the hot, dry summer will pay big dividends!

Submitted by Andrew Rideout, Agent for Horticulture, Henderson Co. Cooperative Extension Service