Spring Thatch ... and How to Manage It

Staff Report

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.

There are a host of issues that challenge the landscape contractor and maintenance professional when it comes to healthy turf grass. One of most common is thatch. Every lawn has thatch, but the health of the lawn can be either benefit or suffer from thatch, based on a 1/4-inch of difference.

What is thatch? How does it impact turf grass, and when it is out of balance, what are the effects and how can landscape contractors control or improve it?

Thatch is a layer of living and dead organic matter that resides between the turf grass green matter and the soil surface. The primary component of thatch is turfgrass stems and roots. It accumulates as these plant parts buildup faster than they break down.

 


Over-watering is one of the contributing factors that can lead to excessive thatch. It makes the lawn grow too fast, which can lead to the excessive buildup of the dead material that makes up thatch. Reducing over-watering and fertilizer use are the two things to look at to discourage the formation of excessive thatch.

Excessive Verses Moderate Thatch

Excessive thatch (more than 1/2 inch thick) impedes proper turfgrass root growth, while also creating a favorable environment for pests and disease. However, moderate thatch levels (1/2 inches or less) are beneficial. Thatch acts as a mulch layer that shades the surface to reduce high summer soil temperature and evaporation, and competes with annual weeds such as crabgrass.

It supplies food sources and a habitat for beneficial microbes. Also, earthworms use thatch's organic matter as a way to burrow into the soil, which aids in reducing soil compaction. It also acts as a living filter to reduce groundwater contamination, while also providing a cushion that reduces turf injury.

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.

Why Excessive Thatch is Bad

Excessive Thatch soaks up water so it cannot reach the soil. As a consequence, 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 combination of biological, cultural and environmental factors.

Reduce Fertilizer and Over-Watering

Heavy nitrogen fertilizer applications and/or over-watering frequently contribute 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 discourage 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 return unless the root cause is corrected.

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 ?EUR??,,????'??excessive.?EUR??,,????'?? 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 ?EUR??,,????'??moderate?EUR??,,????'?? and is beneficial to healthy turf growth.

Core Aerating and Top Dressing

Core aerification is the first step to correct the reasons for excessive thatch buildup. Core aerifying machines pull up small soil cores to the surface that are left as topdressing. The holes created help solve problems 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 problems, and leads to better root systems and healthier lawns. Aerify in spring or fall, making sure adequate moisture exists in the soil.

Make two trips over the lawn, the second perpendicular to the first. Aim for an average of 15 to 20 aeration holes per square foot. Cores should remain on the surface and allowed to air dry.

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.

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.