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Many varieties of lawn grasses (such as Zoysia and St. Augustine) produce large quantities of roots, stems, rhizomes, and stolons that are resistant to decay. That layer of non-decayed organic matter that forms between the soil surface and green vegetation is called thatch. A moderate layer of thatch is a normal occurence in lawns; however, problems may arise when this layer becomes excessive. Thatch can lead to disease, fertilizing, watering, and root problems that may eventually kill grass. In addition, thatch can contribute to an uneven growth height resulting in scalping. A moderate amount of thatch is beneficial to your lawn, but too much can cause turf issues. Less than ¾”-1” of thatch will seldom lead to problems, but a layer exceeding that depth may lead to future issues.
Benefits of a moderate layer of thatch include: insulating the soil to retain moisture, supplying a food source for beneficial microbes, acting as an additional filter to reduce contamination of groundwater, and providing a protective layer to reduce turf damage.
Detrimental effects of an excessive thatch layer include: acting as barrier preventing fertilizer from reaching roots, instances where grass roots in the thatch rather than the soil (this makes grass more likely to suffer from injury or drought effects), harboring disease and insects, interfering with the movement of air and nutrients into the soil, and increasing the potential for scalping.
How do I know if I have too much thatch?
- Lawn feels spongy or soft
- Lawn has dry spots despite watering
- Lawn shows sign of scalping after mowing
- Lawn is thinning and dying even after fertilizing
You can measure thatch by cutting a small plug from your lawn and measuring the cross-section to determine the distance between the soil and the grass.
Preventing Excessive Thatch Buildup
- Maintain a proper mowing schedule that does not remove more than 1/3 of the grass blade length (short clippings do not add thatch)
- Apply appropriate amounts of fertilizer
- Avoid overwatering which can lead to excessive shoot growthand development of disease
- Core aerifying to increase flow of air, water, and nutrients to the root system
- Maintaining a 6.0-7.0 pH in soil to support a healthy environment for microorganisms
Thatch can be removed from your lawn by using a dethatching rake, power rake, or a dethatcher also known as a vertical mower or verticutter. For small lawns or for moderate thatch problems consider using a detaching rake. When done correctly you will feel the thatch separating from the soil as you see it lift to the lawn's surface. Most local equipment rental shops will have dethatching equipment available. When renting a dethatcher, remember to ask the rental agency to set the spacing of the blade specific to the type of grass you will be dethatching. Remember - a dethatcher is a large, heavy machine that will require a lot of strength to operate. If this sounds like too big of a task, there's always the option to hire a professional lawn service company to do the job for you.
Aerifying and topdressing your lawn are also great ways to eliminate excessive lawn thatch. Some of the plugs left on top of the lawn after aerifying can be left there to help decompose the excess layer.
- Mow grass to about half its normal height to allow yourself to observe your progress more easily
- Flag sprinkler heads or other hidden objects in the lawn to avoid damaging them
- For best results, always dethatch in at least two directions that are 90° angles to one another
- After dethatching, a clean up of the debris will be necessary
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