Thatch is located between green vegetation and the soil surface. It consists of a layer of dead and decaying turfgrass tissues derived from leaves, shoots, and roots not from grass that is not bagged.
Thatch accumulates when the rate of turfgrass organic matter productions exceeds its rate of decomposition. Small amounts (less than ½ inch) can be beneficial. Some thatch increases the turf’s resiliency, improves wear tolerance, and insulates against soil temperature changes. Accumulations more than ½ inch reduce heat, cold, and drought hardiness and increase localized dry spots, scalping, disease, and insect problems. As it accumulates, there is a tendency for root and rhizome growth to occur in the layers rather than in the soil. This situation is particularly troublesome since build-up is accelerated by root and rhizome tissue debris.
Without proper management, the turf will become poorly rooted and prone to stress injury.
To determine accumulation, cut a pie-shaped wedge of grass and soil, remove it, and measure the organic matter that has accumulated. Measure the accumulation from several areas in the turf, since thatch is not uniformly distributed. If the layer exceeds ½ inch, the thatch accumulation needs to be reduced.
Thatch can be removed by hand raking or by using a power rake. Hand raking is laborious and is only practical for small areas. Power rakes use rigid wire tines or steel blades to lift thatch debris and a small amount of soil to the turf surface. The soil should be moist for best results. Power raking during excessive soil moisture conditions tears and pulls the turf from the soil instead of slicing and lifting the thatch debris desired. Remove thatch during periods of active turfgrass growth. Removal from cool season turfgrasses, like Kentucky bluegrass, is best done in the early spring and in the fall after Labor Day. Remove when at least 30 days of favorable growth conditions will occur after dethatching. Removal in the spring requires an application of preemergent herbicide to prevent establishment of annual weeds.
Core cultivation (aerification) can be used to minimize accumulation, to modify its physical characteristics, and to removed limited amounts of thatch. Core cultivation is not as effective as power raking in removing debris but is more effective in reducing thatch accumulation rate. A combination of soil cultivation and aeration is a preferred program to modify and reduce build-up.
If mechanical removal is necessary, do it when the turf is actively growing to aid in recover. Fall is the preferred time because weed competition is minimal. Spring is an acceptable time but apply a preemergent herbicide after dethatching to prevent establishment of annual weds. Power rake lightly, removing no more than ½ inch at a time. If it is excessive, it may require several spring and fall treatments. In some cases, it may be necessary to completely renovate or reestablish the turf.
R. E. Gaussoin, J. Kruskoci, and D. Steinegger. (1997). Integrated Turfgrass Management. In F. Baxendale, Ph.D., & R. Gaussoin, Ph.D., Integrated Turfgrass Management for the Northern Great Plains (pp. 24 – 27). Location: Nebraska