St. Augustine grass is a popular warm-season turfgrass in the southern United States, known for its aggressive, carpet-like growth. It spreads quickly via above-ground runners called stolons. Thatch is the layer of organic material—including dead stems, leaves, and roots—that accumulates between the soil surface and the green grass blades. While a thin layer is beneficial, excessive buildup prevents water and nutrients from reaching the soil, causing a decline in lawn health. Understanding the grass’s unique anatomy is crucial when considering thatch removal.
Identifying Thatch in St. Augustine Grass
Homeowners should determine if a thatch problem exists before attempting removal. A small amount of thatch, typically less than one-half inch thick, is beneficial, insulating the soil and cushioning the turf. When this layer exceeds one-half to three-quarters of an inch, it becomes problematic. It creates a barrier that impedes the movement of air, water, and fertilizer into the root zone, encouraging shallow rooting and leaving the grass susceptible to stress.
You can check for thatch by cutting a small, triangular section of your lawn and examining the soil profile. Use a sharp knife or trowel to lift a piece of sod and observe the distinct layers between the green blades and the underlying soil. The spongy, fibrous, brownish layer that is not soil is the thatch.
Why Traditional Dethatching is Risky
Traditional mechanical dethatching, often done with a power rake, uses aggressive rotating tines to rip organic material out of the turf. This method is extremely risky for St. Augustine grass due to its unique growth structure. St. Augustine grass spreads exclusively through horizontal, above-ground runners called stolons, which are the plant’s primary growth mechanism.
The aggressive action of a standard dethatcher can severely damage or completely tear up these stolons. Unlike turfgrasses that have protective underground stems (rhizomes), St. Augustine grass has no below-ground stems for recovery. Damaging the stolons causes significant turf injury and can leave behind large, bare patches that the lawn will struggle to recover from.
Alternative Thatch Reduction Techniques
Since traditional dethatching is risky, homeowners must use safer, less invasive alternatives to manage excessive thatch build-up. If the thatch layer is greater than one inch thick, vertical mowing or “verticutting” is the preferred mechanical method. A verticutter uses vertical blades spaced several inches apart to slice through the thatch and slightly into the soil, removing dead material without tearing up the stolons.
This process should only be performed when the St. Augustine grass is actively growing, typically in the late spring to early summer, to allow for quick recovery. The machine’s blades should be set no closer than three inches apart to minimize damage to the runners. Following verticutting, the debris must be raked and removed, and the area should be immediately irrigated.
Core aeration is another effective technique, involving the removal of plugs of soil and thatch from the lawn. This process helps relieve soil compaction and introduces air and moisture, encouraging microbial activity necessary to naturally break down the thatch layer. Topdressing the lawn with a thin layer of compost or sand after aeration can further boost microbial decomposition and is considered the best method for long-term thatch control.
Cultural Practices to Minimize Thatch
The best approach to thatch management is prevention through consistent, proper cultural practices. Avoiding excessive nitrogen fertilization is important, as over-fertilizing promotes rapid shoot growth that contributes to organic matter buildup. Using a slow-release nitrogen fertilizer, applied at the correct rate, helps maintain steady growth rather than encouraging sudden bursts.
Proper mowing is also essential; never remove more than one-third of the grass blade height in a single session. St. Augustine grass should be maintained at a height between three and four inches, as cutting it too short stresses the plant and increases thatch formation. Watering deeply and infrequently encourages roots to grow down into the soil, promoting a healthier overall turf.