Yard and Garden: Thatch and Fall Removal

August 21, 2019, 4:23 pm | Richard Jauron, Willy Klein

Leaves fallen on grass field by worldwide_stock/stock.adobe.com.AMES, Iowa – Thatch can be problematic and beneficial to lawns. Thatch supplies necessary food sources for microbes and organic matter. However, excessive thatch can harbor diseases and insects. Thatch that is properly balanced promotes growth and appearance of a well-groomed lawn. Horticulturists with ISU Extension and Outreach answer questions about thatch and fall removal. 

What is thatch?  

Thatch is the layer of dead and living plant material that accumulates above the soil surface in lawns. Thatch is composed primarily of shoots, crowns and roots. Contrary to popular belief, grass clippings do not contribute significantly to thatch buildup. When lawns are mowed properly, grass clippings break down quickly.  

Thatch, to some degree, is present in all lawns. A small amount of thatch is beneficial as it moderates soil temperatures. However, thatch becomes detrimental when it is present in amounts greater than ½ inch. Excessive amounts of thatch increase the potential for turf damage due to drought, extremes in temperature, diseases and insects.

Compacted soils and heavy, clay soils are prone to thatch buildup. Heavy nitrogen fertilization and over-watering promote thatch accumulation.  

How do you remove thatch?  

Thatch layers of ½ inch or greater can be removed with a vertical mower or power rake. The vertical mower has evenly spaced knife-like blades that rotate perpendicularly to the thatch surface. The vertical mower blades slice through the thatch and about ¼ inch into the soil. After vertical mowing, hand rake the loose thatch from the lawn. A powder rake has spring steel tines that loosen thatch without cutting into the soil. Vertical mowing and power raking services are available from professional lawn care companies. For individuals who prefer to do things themselves, vertical mowers and power rakes are often available at rental agencies.

When is the best time to remove thatch from the lawn?  

September is the best time to dethatch Kentucky bluegrass lawns. The slicing and ripping action during dethatching injures the grass. Dethatching the lawn in September gives the turfgrass several weeks of favorable weather in which to recover.  

How do I prevent the buildup of thatch?  

Good lawn care practices can prevent the buildup of excessive amounts of thatch. Fertilize the lawn moderately. A single application of fertilizer in late October/early November is usually sufficient for low maintenance lawns. Highly maintained lawns may be fertilized in spring, September and late October/early November. Do not apply more than one pound of nitrogen per 1,000 square feet in a single application. If you decide to water the lawn in dry weather, apply 1 to 1½ inches of water per week in a single application or two applications three or four days apart. Core aerate lawns established on heavy, clay soils and soils that have become compacted.  

Photo credit: worldwide_stock/stock.adobe.com

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