Prevent thatch from building up in lawns
By Ray Ridlen
The best lawn grasses are those that constantly reproduce new plants, renewing the lawn. As old plants age and die they decompose into fine-textured humus, which becomes part of the surface soil.
Any time decay is slowed by unfavorable conditions, thatch, composed of old clippings, roots and stems, builds up.
Thatch buildup varies among lawns, some never developing a thatch layer while others become thatch-bound within a few years after the lawn is established. Excessive growth, overgrowth followed by severe cutting, clippings left on the lawn, fungus disease, prolonged diseases, and conditions unfavorable to micro-organisms are some factors which favor thatch development.
Rapid, excessive growth is likely to produce a heavy thatch because plant material is being produced more rapidly than it can decompose.
Once thatch formation starts, conditions develop that may favor additional formation. Accumulation of thatch harbors disease-causing fungi and insects; prolongs high humidity, which favors disease; causes shallow root development; and retards movement of air and water into the soil.
As thatch builds up, roots of new grass plants grow within the thatch layer rather than in the soil. Exposure to hot, dry summer weather makes it difficult for plants to survive.
Zoysia and bermudagrass lawns usually develop thatch layers rapidly but seldom die suddenly since they are more heat and drought tolerant. Severe thatch in the warm-season grasses usually leads to thin, diseased turf, and thick thatch layers may cause uneven and difficult mowing.
Thatch may develop over a period of years before noticeable damage occurs. Good cultural practices, beginning when the lawn is new, may not prevent thatch indefinitely, but can retard its formation. Some desirable practices are:
--Moderate, regular fertilization of soil to maintain vigor without excessive growth.
--Regular cutting at recommended height to maintain vigor and avoid shock.
--Collection and removal of clippings, especially during periods of rapid growth.
--Deep-soak irrigation every 10 to 14 days in dry periods to encourage deep rooting.
--Raking annually before the new flush of growth begins.
--Aerating soil to improve penetration of water and fertilizer.
Examine the lawn closely regardless of how healthy it appears. Cut and lift plugs two or three inches deep. Examine the profile of the plug. If thatch is present, it will appear as a distinct layer of stringy or felt-like material.
Thatch should be removed in fescue when about one-third inch of thatch develops before grass is damaged. Moderate layers may be removed by vigorous hand raking. Thick layers are best removed by a de-thatching machine or power rake that may be hired or rented.
Cool-season lawns rarely develop thick thatch in Oklahoma. Use moderation when removing thatch from these grasses. February and March are preferred months for de-thatching zoysia and bermuda lawns.