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Thatch is a tightly interwoven layer of living and dead grass stems and roots lying between the soil surface and green grass leaves in established lawns. Thatch originates from old stems, stolons, roots, and rhizomes shed by grasses during the development of new plant parts or rapid die-back due to drought, disease, insects, etc. When the accumulation rate of plant litter exceeds the decomposition rate, a thatch layer develops.

The problem of thatch build-up was once thought to be associated with leaving grass clippings on the lawn, when in fact, the two are not strongly connected. Thatch is produced from the fibrous portions of the grass plant and results from the abnormally fast growth of tissues high in lignin (an organic polymer that provides strength to cell walls), such as roots, rhizomes, stolons and crowns. Grass clippings themselves are not high in lignin, but are composed mostly of cellulose and water. Grass clippings decompose rapidly.

A thin layer of thatch is normal (even healthy) since it retains some moisture in the soil and increases wear tolerance. Symptoms of excessive thatch include:   

  • Grasses become less drought tolerant and more susceptible to heat injury, wilting and drying out.
  • Thatch dries out rapidly, and after drying out, rewets with difficulty. Thatch layers greater than one-half inch require more frequent irrigation.
  • Increased disease and insect problems. This “organic barrier” reduces the effectiveness of fungicides and insecticides while providing an ideal environment for these pests and insulating them from winter freeze.
  • Results in poor rooting of turf over time. Since the thatch layer retains fertilizer and moisture it encourages root growth there instead of deeper into the soil below.

What Can I Do About Thatch?

There are three choices.

  • You can ignore the thatch, and hope it will decay before it does any harm. However, a thatch problem will always get worse with time, not better.
  • You can power rake or dethatch your lawn. Dethatching lawns is labor intensive, extremely disruptive, and expensive. It is a management tool that should only be used in terminal situations. Dethatching involves cutting and slicing a lawn vertically with blades or tines. After dethatching a lawn, dead material should be raked and hauled off the lawn. Typically a lawn that is mechanically dethatched will need to be completely reseeded because most of the quality grasses were ripped out along with the thatch. A ‘light’ mechanical dethatching usually does no good because it only removes dead grass on the surface and barely touches the deeply woven thatch layer.
  • The third alternative (the option recommended by Bio Green) is core aeration. Core aeration is considered a ‘biological’ dethatching. Core aeration offers the least amount of disturbance to the healthy plants and at the same time has benefits to the lawn in addition to thatch reduction.
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