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Aerate, Don't Power Rake to Remove Lawn Thatch

By Carl Wilson, Colorado State University Cooperative Extension Agent, Horticulture, Denver County

With summer's onset, lawns often lose their lush green and replace it with a brown undertone. Regular watering every three days may not be enough to maintain a deep green color.

Kentucky bluegrass is a cool season grass that does not grow well in summer's heat, but thatch is the chief cause of summer browning. Thatch may be the most misunderstood part of lawn care. What it is and how do we to rid a lawn of it?

Thatch is the dark brown, felt-like material between the soil and the base of the grass plant. On first glance, it easily is mistaken for soil.

Thatch starts with thick grass stems and roots. When these hardened grass parts die, they break down slowly and can accumulate as a thatch layer. If thatch builds up to 3/4 inch or more, lawn care becomes difficult and brown grass undertones develop.

With thatch build-up, irrigation water runs off instead of penetrating the soil. Soil in heavily thatched lawns may never become wet at all. If the thatch eventually is moistened, it soon becomes soggy and too wet for healthy grass root growth. Either way, the grass takes on the brown undertone of a drought-stressed lawn.

What can be done to avoid or solve lawn thatch problems? First, let grass clippings lie on the lawn. They break down quickly and encourage the growth of microorganisms that also digest thatch. Second, avoid overuse of pesticides, especially fungicides. These chemicals kill the microorganisms that break down thatch.

Third, core aerate at least once per year, more often if thatch has already become a problem. A bit of thatch is sliced out with each core, allowing water and air to better penetrate the soil. Core aeration has replaced the earlier power raking technology of the 1950's. Even so, you may need to core aerate several times per year over several years to remedy a serious lawn thatch problem.

Other lawn care practices such as regular fertilizing, watering and mowing as well as minimizing pesticide applications also are a part of solving thatch problems.

Photograph courtesy of Angelina Sedbrook

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Date last revised: 01/05/2010