Thatch Depth & Lawn Dethatching Assessment Tool

What Is Lawn Thatch (And What It Isn't)

Thatch is a tightly interwoven layer of living and dead turfgrass stems, crowns, stolons, and roots that develops between the green vegetation and the mineral soil surface.

Common Myth: Grass clippings do not cause thatch. Clippings are over 80% water and contain minimal lignin, decomposing rapidly via microbial action within days. Thatch is composed almost entirely of high-lignin vegetative tissue—primarily stems and root crowns—that resists natural biological degradation.

The 1/2-Inch Agronomic Threshold

• Under 1/2 Inch (Beneficial): A thin thatch layer is highly desirable. It acts as an organic mulch, cushioning foot traffic, moderating root zone soil temperatures, and reducing surface evaporation.
• Over 1/2 Inch (Detrimental): When thatch exceeds 0.5 inches (12 mm), grass roots begin growing horizontally inside the spongy thatch layer rather than anchoring deep in the mineral soil. During dry summer spells, thatch becomes hydrophobic, repelling irrigation water and causing severe localized dry spots.