Thatch is the accumulation of undecomposed or partially decomposed organic matter (living and dead roots, crowns and stems of grass) that is found at the soil surface below the grass blades. When organic matter accumulates faster than it can be decomposed, thatch results. A thatch layer is good if it is less than ¾” because it can absorb some shock, provide some cushioning and minimize to some degree the potential for player injury. However, levels greater than ¾” can cause shallow rooting and negatively affect turf health.
Excessive thatch levels make it difficult for water, fertilizer and pesticides to reach the soil. Yet the thatchy area is ideal for pathogens to thrive and when the turf is stressed the likelihood of patch diseases, for example summer patch, increases. Also when the thatch layer is high it can elevate the crown which can be scalped during mowing. When thatchy turf dries out it is very difficult for the water to infiltrate into the canopy and reach the soil, thus creating “hydrophobic soils”.
Some organic matter accumulation is normal, but grasses such as Kentucky bluegrass are thatch producers. Improper pH, compacted soils and poor drainage encourage thatch build up. So thatch management strategies include: keeping the soil pH in the proper range, core cultivating and topdressing – all practices within the turf manager’s control.