Thatch is a roofing material made from dried plant stalks like straw, reeds, or palm leaves, bundled tightly together and layered to keep rain out. For thousands of years, people built homes with thatched roofs because the materials grew nearby and cost nothing. A skilled craftsperson called a thatcher would weave and tie the dried plants into thick layers, sometimes two feet deep, creating a roof that could last 30 years or more.

Thatched roofs work surprisingly well. The tight bundles shed water like a duck's feathers, and the thick layers provide excellent insulation, keeping homes cool in summer and warm in winter. You can still see thatched cottages throughout England, Ireland, and other parts of Europe, though now they're preserved more for their beauty and historical value than necessity.

The word also describes the layer of dead grass and plant material that builds up in lawns. When gardeners talk about dethatching their lawn, they mean removing this mat of dead growth so water and nutrients can reach the soil. Too much thatch in your yard works like a blanket, preventing healthy grass from growing underneath.