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Above: Core aerification followed by topdressing are two methods that help correct excessive thatch buildup. The holes created help solve problems such as compactionand poor drainage. Topdressing adds a layer of soil over the thatch, which adds microorganisms to help break thatch down to healthy levels.
Left: Depending on how deep the thatch is, mechanical dethatching can destroy the lawn because the grass roots are in the thatch instead of soil, so the roots tear out easily. If over-seeding is required afterwards, it's best to tear out thatch in late August for optimum over-seeding timing.
Above, Inset: Thatch is the layer of living and dead organic matter residing between the turf grass green matter and the soil surface. A thatch depth that exceeds 1/2 inch is considered "excessive." It impedes lawn growth because the roots grow into the thatch layer and not the soil. A layer less than 1/2 inch deep is considered "moderate" and is beneficial to healthy turf growth.
Above, right: Adding materials (topdressing) in thin layers over turf makes it possible to add organic amendments and gradually improve the underlying soil without disturbing the actively growing grass. The microorganisms within the top dressing help to break down thatch, as well.
moisture and nutrients don't make it to the grass' roots system, preventing them from developing the depth necessary for drought resistance and long-term good health. In addition, excessive thatch provides optimal conditions for diseases like Brown Spot and the perfect breeding ground for insects and grubs. Thatch problems result from a com- bination of biological, cultural and environ- mental factors.
Reduce Fertilizer and Over-Watering Heavy nitrogen fertilizer applications
and/or over-watering frequently contrib- ute to thatch, because they cause the lawn to grow excessively fast. Reducing fertilizer use and over-watering are the two simplest things a landscape contractor can do to dis- courage the formation of excessive thatch. Short clippings dropped on the lawn after mowing are not the cause of thatch buildup.
Clippings are very high in water content and breakdown rapidly when returned to lawns after mowing, assuming lawns are mowed on a regular basis. The three main environmental culprits
that encourage excess thatch are: Heavy, wet soils; alkaline (high pH) soils; and soil compaction. Thatch may be torn out with a dethatcher
or vertical mower, but will most likely re- turn unless the root cause is corrected.
Core Aerating and Top Dressing Core aerification is the first step to cor-
rect the reasons for excessive thatch build- up. Core aerifying machines pull up small soil cores to the surface that are left as top- dressing. The holes created help solve prob- lems such as compaction and poor drainage. They also allow water direct access to the root structure.
Aerification Benefits Aerification is an excellent lawn practice
with many benefits, as it helps solve soil prob- lems, and leads to better root systems and healthier lawns. Aerify in spring or fall, mak- ing sure adequate moisture exists in the soil. Make two trips over the lawn, the second
perpendicular to the first. Aim for an av- erage of 15 to 20 aeration holes per square foot. Cores should remain on the surface and allowed to air dry.
Topdressing Topdressing is simply adding a 1/8 to
1/4-inch layer of compatible soil over the thatch, which adds microorganisms to help break it down. Understanding thatch and knowing how
to correct it when it becomes too deep will lead to the healthy lawns your clients are looking for.
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