What is the approximate thatch depth at which infiltration and gas exchange begin to be restricted?

• A. 0.25 inch
• B. 0.5 inch (12–13 mm)
• C. 1.0 inch
• D. 2.0 inches

Answer: (B)

Infiltration and gas exchange start to be restricted when the thatch layer becomes thick enough to impede movement of water and air between the soil and the surface. About half an inch of thatch (roughly 12–13 mm) is the point where these processes begin to show measurable decline. A thinner thatch, like 0.25 inch, generally doesn’t hinder infiltration, while a thicker layer (1 inch or more) worsens the restriction quite a bit. This is why the threshold is around 0.5 inch: it marks the onset of noticeable limitations to water entry and soil oxygen, which can impact root health. Managing thatch through dethatching or aeration helps restore proper infiltration and gas exchange.