Thatch can smother lawn if not removed

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Thatch buildup can be a problem for lawns. Thatch is a layer of living and dead roots, crowns and lower shoots that develop in lawns. It can weaken and even destroy a lawn if not removed.

Factors favorable to thatch development include excessive growth and conditions unfavorable to the microorganisms that decompose decaying plant parts. Rapid and excessive growth is likely to produce a heavy thatch because plant material is being produced more rapidly than it can decompose. Golf courses and athletic fields typically have more of a thatch problem because of their high management levels on the grass.

Contrary to what most people think, grass clippings from mowing do not contribute to thatch. However, once a thatch layer has developed, clippings can further speed its formation.

Thatch buildup varies among lawns. Some lawns never develop a thatch layer, while others become thatch-bound within a few years after being established. The best lawn grasses are those that constantly reproduce new plants to renew the lawn. As old plants age and die, they decompose into fine-textured humus that becomes a part of the surface soil.

Once thatch starts to form, conditions develop that might favor even more thatch. Accumulated thatch harbors disease-causing fungi and insects; prolongs high humidity, which favors disease; causes shallow root development; and retards movement of air, water and nutrients into the soil.

These factors contribute to early death of the grass plants. So thatch is both a result of unfavorable conditions and a cause of further damaging influences.

Thatch development can go unnoticed in the early stages. Lawns with a thick layer can appear healthy in the spring, then suddenly die in large patches during summer’s heat and drought. As thatch builds up, the roots of new grass grow within the thatch layer rather than in the soil. When the lawn is exposed to hot, dry summer weather, the plants are not able to survive.

Zoysia and Bermuda can be two grasses that develop thatch layers rapidly, but seldom die suddenly because of their tolerance to heat and drought. Severe thatch usually leads to thin, diseased turf. Or very thick layers of thatch can cause uneven and difficult mowing.

Thatch might develop over several years before noticeable damage occurs. Good cultural practices, starting when the lawn is new, might not prevent it indefinitely, but can retard its formation.

There are several good cultural practices to help prevent thatch buildup:

1. Fertilize moderately and regularly to maintain vigor without excessive growth.

2. Cut grass regularly at the recommended height to maintain vigor and avoid shock. No more than 1/3 of the leaf tissue should be removed with each mowing. Remove excess clippings, especially during periods of rapid growth. Clippings can be left to decompose if mowing occurs at regular intervals. Nutrients are recycled as the clippings filter into the turf canopy and decompose.

3. Collect and remove clippings once a thatch layer has begun to develop to avoid further buildup.

4. Irrigate every seven days, or as needed in dry periods to encourage deep rooting. Don’t overwater.

5. Rake out the thatch as needed to keep it below ½ inch thick. You can rent a dethatching machine but I recommend them on only zoysia and Bermuda. Using them on centipede and St. Augustine tears up the grass, so a better way to dethatch on these grasses is to topdress with ¼ inch of weed-free soil. Topsoil contains millions of microorganisms that will aid in the decay of thatch. Don’t use pure sand as it does not contain the microorganism of soil. Early to midsummer is the best time to do this.

6. Core aerify to improve penetration of water and fertilizer. Leave soil cores on the surface to dry and crumble before mowing. Mowing the dried soil cores will redistribute the soil microbes that decompose soil and thatch and will aid in reducing thatch.

7. Remember that earthworms are good guys since they naturally reduce thatch as they collect it from the surface and mix it deeper into the soil.

Have a great and safe Fourth of July!


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