Thatch is a tightly intermingled layer of living and dead stems, roots and leaves that develops between the layer of green vegetation and the soil surface, Unless removed, thatch will often develop into a layer of 1 inch or more in several years. Thatch will develop faster on a vigorous, high quality lawn than on a low quality lawn.



An excessive thatch accumulation creates conditions that may result in deterioration of the lawn: 1) increased disease susceptibility, 2) restricted rooting, 3) less resistance to drought and other environmental stress conditions and 4) less water and fertilizer availability.
The overall effect of a thatch layer is an unthrifty lawn that does not respond well to management practices and that is easily injured when conditions are not optimum for growth.



Fertilization, under certain conditions, increases thatch accumulation by producing more vegetation material that does not decompose as rapidly as it is produced. More thatch accumulate under infrequent and high mowing; however, grass should not be mowed shorter than recommended. Thatch accumulation is increased on soils that are very acid or alkaline and on poorly drained soils. Grass clippings should not be removed because they are a valuable source of nutrients and do not contribute to thatch accumulation. Research has shown that earthworm activity is important in avoiding excessive thatch accumulation. Earthworms feed on thatch as well as other forms of organic matter found in the soil. Any management practice that may harm the native earthworm population in the turf area should be avoided, particularly the excessive or indiscriminate use of certain pesticides.



The proper use of powered machines (rakes, vertical mowers, etc.) designed to remove thatch is probably the best solution. Thatch should be removed whenever the layer is 0.5 inch or more thick. It should be done as needed and not as a routine practice. The soil should be moist for better thatch removal and plant regrowth.

Limited experience indicates that early fall is the best time for removing thatch because of less competition from annual grasses. Early spring is an acceptable time for dethatching, but weeds and other problems are usually more likely to occur. In most cities you can buy or rent machines for removing thatch. Joint purchase by a group of neighbors is a logical approach to making a thatch removing machine available. For small lawns, special hand thatch rakes may solve the problem.