What is thatch?

During the year, dead plant material, rotting grass cuttings and other decaying organic matter accumulate on the soil surface at the base of the grass, producing thatch. Not all thatch is bad: a thin layer, 13mm (½in) or less, is actually beneficial because it insulates the soil, helping to prevent the grass roots from drying out. However, when a thick layer of thatch builds up, it prevents water, air and nutrients from percolating through the soil, reducing the health of the grass. These conditions can also encourage waterlogging, moss, weeds and turf fungal diseases.