What is thatch?

Thatch is a loose (spongey) intertwined accumulation of both dead and alive grass roots, stems, and shoots. This layer exists in-between the actual soil surface, and the green vegetation. Thatch occurs when growth outpaces the rate at which it can be broken down by soil organisms. A small amount of thatch is healthy as it can help insulate the majority of your lawns root system from extreme temperatures as well as help to retain soil moisture. Too much thatch can greatly inhibit the flow of air, water, and nutrients into the soil.

What causes thatch?

Thatch occurs when growth outpaces the rate at which it can be broken down by soil organisms. The primary factors that contribute thatch development include: grass type, aggressive fertilization, heavy irrigation, acidic soils, heavy/compacted soil, and soils low in organic matter. When a combination of these conditions are present, thatch is likely to accumulate at a rate beyond what is decomposing. This is why having a “healthy” or “living” soil is important as it relates to maintaining a great lawn.

When is thatch a problem?

When a thatch layer exceeds ~1/2-3/4 inch, it is common to see problems arise.

Why is too much thatch a problem?

Excess thatch can greatly inhibit the flow of air, water, and nutrients into the soil.

Water- The thatch layer is prone to heating up and cooling down more quickly than your soil. When temperatures increase, this layer dries up rapidly. If a large amount of the grass plants living roots are entangled in this layer, . For cool season grass types to tolerate summer conditions, the roots need to be healthy and growing down-wards into the soil. When irrigation is applied (sprinklers or rainfall) the thatch layer can trap moisture above the soil line. This can contribute to common diseases such as “brown patch” in the summer or “red thread” in the fall/winter.

Air - In the cooler months, a dense thatch layer can trap soil moisture by slowing evaporation. A soil that is perpetually water logged will have reduced oxygen levels. This leads the grass to decline and potential die-off if conditions persist. Making matters worse, low oxygen levels will have a detrimental effect on beneficial soil microbe populations. Some of these microbes are responsible for decomposing thatch.

Nutrients - A dense thatch layer can restrict supplemental nutrients from entering the soil, essentially trapping them at the surface.

Pests -