Most grasses that develop stolons (above-ground stems) or rhizomes (below-ground stems) are susceptible to excessive thatch buildup. Grasses with greater lignin content are more prone as well because lignin is harder for microorganisms to break down. Grass types that are susceptible to thatch: Cool-season grasses: --Creeping bentgrass  --Creeping red fescue  --Kentucky bluegrass  Warm-season grasses: --Hybrid bermudagrass  --Centipedegrass (only if over-fertilized)  --St. Augustinegrass --Zoysiagrass  Grass types that are not susceptible to thatch: --Perennial ryegrass (bunch-type cool-season grass) --Tall fescue (bunch-type cool-season grass)