Zoysia grass (Zoysia spp.) is a warm-season perennial grass native to southern Asia. Typically three species are used as turf grass in lawns, or various cultivars and hybrids of them. Some species of zoysia grass are commonly called "Manila grass," "Japanese lawn grass," "Korean velvet grass" or "Mascarene grass," according to Texas A&M University. Zoysia grasses are grown in the southern half of the United States, becoming straw-brown in the cool months. They grow well in any well-drained soil in abundant sunshine and tolerate salt spray near coastal locations.
What is Thatch?
When discussing zoysia grass lawns, "thatch" refers to the excessive buildup of dry blade clippings. Texas A&M University describes the thatch as a layer of non-decomposed organic material that rests just above the soil surface.
Thatch builds up when zoysia grass is improperly cut, such as allowing the leaf blades to grow tall and then cutting more than one-third of the blade. The clipping refuse when improperly mowed accumulates at a rate and density that slows natural decomposition. The fragments drop between the green blades and stack up on the soil surface around and atop the zoysia grass plants' stems and roots.
Excessive buildup of thatch on zoysia grass lawns causes a mulch or barrier-like covering on the soil under the plants. This causes shading and cooling of the soil, decreased air circulation around grass stems and potential for fungal problems. If thatch is very dry or thick, it will block rain or irrigation from reaching and penetrating into the soil.
Texas A&M University cites many techniques to diminish concerns with thatch in a zoysia grass lawn. First, maintain the lawn by cutting it at a height of 1 to 2 inches. This often equates to mowing every five to seven days during summer and early autumn. Never cut more than one-third of the total height of the grass, even if a few skipped mowings finds the lawn tall. Cutting tall zoysia grass too short at one time removes all green leaves and exposes the tan sheaths/stalks of the lower parts of the plant. This is referred to as "scalping."
Once thatch reaches concerning levels in the zoysia lawn, vertical mowers or flair mowers are used to remove excessive thatch. This process is best done before the end of summer to allow the grass to regrow before the onset of cool fall weather that naturally brings on dormancy. Some turf specialists scalp their zoysia grass lawn, mowing it low at 1/2 to 1 inch tall in early spring before new late spring growth emerges. This diminishes likelihood of excessive thatch buildup later in the year if proper mowing heights are maintained.