Thatch is the interwoven layer of decomposing organic material that accumulates between lawn grass and topsoil. It consists of dying roots, cut grass, leaves and twigs. In a healthy lawn the thatch will be half an inch thick and can be seen by vertically cutting a piece of turf from the lawn. Thatch provides nutrients to the soil as it decays. However, if it becomes too thick, it can prevent air and water from reaching the soil and lead to compaction. The purpose of dethatching is to reduce the thatch layer but not to remove it entirely.
Cut out a small section of turf with a spade. A piece that is roughly four to six inches square and about six inches deep is plenty. Measure the depth of the thatch from the top of the soil to the bottom of the green grass. You will need to dethatch if the thatch layer is more than half an inch thick. Replace the turf when done and tamp it down with your foot.
Mow the lawn to about one inch in height and bag the clippings before dethatching. This will make the raking easier. Dethatching by hand is very hard work and tough on the hands. Use a good pair of work gloves to prevent blisters. A thatching rake has double-sided blades with sharp, V-shaped tines designed to cut through the thatch. Push the tines of the rake far enough to get below the thatch layer. Pull the rake toward you firmly while maintaining enough pressure to tear through the thatch.
Rake each area two or three times to make sure you have removed as much thatch as possible. Look at the material as it is being pulled up. If you see grass, it means that the tines are too deep and are cutting through the roots of the grass. Raise the rake slightly and continue. A good dethatching will remove a lot of material. Throw some on your compost pile if you have one and bag the rest for disposal.