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Thatch Buildup in the Lawn

Glenn Hardebeck
Turfgrass Research Agronomist, Agronomy Department

Thatch is a layer of both dead and living shoots, stems and roots that accumulate just above the soil surface. Thatch accumulates when turf growth surpasses microbial breakdown. Turfgrass leaves are of little consideration in thatch accumulation since they are readily broken down, whereas the roots and stems break down slowly and are actually recognizable within the thatch layer. Grasses likely to have a thatch problem include Kentucky bluegrass, Creeping bentgrass, and most warm-season grasses (Zoysia, Bermuda, ect).

Proper assessment of a lawn’s thatch layer is important because thatch is not a four-letter word. A small to moderate amount (1/4 to 1/2") of thatch provides a cushion against the soil surface and reduces soil temperature fluctuations. Excessive thatch (1/2" or more) in a lawn restricts water and air movement, reduces fertilizer and pesticide response, increases disease problems and grub activity, and may result in shallow rooting primarily within the thatch layer predisposing the turf to drought.

As we get closer and closer to the dog days of summer, thatchy lawns are going to become troublesome to maintain. Samples collected with grub damage, disease problems and localized dry spots often have an underlying thatch problem that needs to be addressed both directly through aerification and dethatching and indirectly through proper turf management practices to reduce the buildup. For more information, check AY-7: "Irrigation Practices for Homelawns", AY-8: "Mowing, Thatching, Aerifying, and Rolling Turf" and AY-22: "Fertilizing Established Lawns".

Click on the small image to view a larger image.

Thatch in Kentucky Bluegrass Thatch in Kentucky Bluegrass
Thatch in Kentucky Bluegrass
(Photos by Glenn Hardebeck)

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Last updated: 12 June 2002/tlm.
The Plant & Pest Diagnostic Laboratory at Purdue University.