Prepared by Bob Polomski, Extension Consumer Horticulturist, and Nancy Doubrava, HGIC Information Specialist, Clemson University. (New 05/99.)
Thatch is a dense, spongy collection of living and dead grass stems and roots lying between the soil surface and green grass leaves in established lawns. As a grass plant grows, the older sloughed-off plant matter from stolons (above-ground stems), roots, rhizomes (below-ground stems) and stems is often slow to decompose and begins to accumulate at the soil surface forming this thatch layer.
A thatch layer greater than ½ inch thick makes watering difficult, since thatch dries out quickly and is difficult to rewet. It also restricts the movement of pesticides, thus reducing their effectiveness. Nutrients and water cannot be properly absorbed by the grass roots that tend to grow into this area.
Grasses differ in their tendency to produce thatch. Tall fescue and perennial ryegrass have a low tendency for producing thatch. Heavy thatch builders include hybrid bermudagrass cultivars and Kentucky bluegrass, mostly due to their vigorous growth rates. Slower growing grasses, such as zoysiagrass, produce thatch because their fibrous tissues are very slow to break down and easily accumulate on the soil surface.
A shallow thatch layer up to ½ inch thick actually benefits the lawn, by helping to retain moisture and stabilizing soil temperature. Examine the depth of the thatch layer by cutting out a pie-shaped wedge of sod from your lawn with a knife or spade. If the thatch layer exceeds ½ inch in thickness, then you need to dethatch your lawn.
Remove thatch in the late summer or early fall for cool-season lawns. Dethatch warm-season grasses in the spring after green-up or in the early summer when it is growing rapidly. Avoid hot and dry periods.
Small areas: Small areas can be dethatched using a dethatching rake. As you pull the rake across the lawn, the sharp curved blades slide through the thatch and lift it from the lawn.
Large areas: Large areas require power-driven dethatching equipment and know-how. You can either hire a reputable commercial lawn care company or attempt it yourself. Improper dethatching can devastate a lawn.
Excerpted from the South Carolina Master Gardener Training Manual, EC 678.
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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.