JoAnne Skelly: Managing thatch starts with preventing its development

Recently I’ve seen a lot of thatching being done on lawns around town. Thatch is the spongy layer of compacted roots that builds up in a lawn. This happens for a number of reasons. Certain grass types with running roots called rhizomes, such as Kentucky bluegrass or creeping red fescue, are more likely to develop thatch. Bunch-type grasses, such as perennial rye or tall fescue, rarely have thatch. Compacted soils and soils low in organic matter and soil microbial activity are subject to thatch.

Managing thatch starts with preventing thatch development in the first place. This requires selecting appropriate species to plant when starting a lawn; preparing soil thoroughly before planting to allow good air and water penetration; using fertilizers and pesticides correctly and at the right time of year; and irrigating properly. Core aeration on a regular basis is a good method to prevent thatch development in an established lawn.

Leaving short clippings on the lawn after mowing does not contribute to thatch, unless there is a dense existing thatch layer. If thatch reaches three-quarters of an inch or more, preventative measures alone won’t eliminate it. At that point, a vertical mower with blades perpendicular to the soil or a power rake will be needed to slice down and through the thatch bringing it up to the surface, so you can rake it up and carry it away. It is better to remove a small amount of thatch in the first pass in order to see how much thatch remains and whether a second pass is needed. Too much thatch removal can damage a lawn and allow weeds to grow.

Don’t remove thatch from a droughty, heat-stressed or weak lawn. Unhealthy lawns may not recover from the thatching process. The best time for thatching is early fall when the weather is cool so the lawn can recover quickly without being stressed.

Core aeration or “aerating” reduces or prevents compaction and improves air and water movement into and through soils by the removal of plugs of soil. Spiking machines that do not pull a plug out actually increase compaction and decrease turf health Plug removal, followed by a top-dressing of organic matter and a deep irrigation, increases the microbial action, which decomposes thatch. Core aeration also helps remove existing thatch. Spring is an excellent time to aerate in Northern Nevada.

For more information, see “Managing Thatch in Lawns” from Penn State Plant Science Department: http://plantscience.psu.edu/research/centers/turf/extension/factsheets/thatch .

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at skellyj@unce.unr.edu or 887-2252.