Thatch is the layer of organic material that builds up in a lawn below the green grass blades and on top of the soil surface. Thatch is made up of dead grass clippings, dead stems and dead surface roots. The lawn grass’s stems will run through the thatch layer and the grassroots may grow into the layer.
A layer of thatch about 1 cm thick is good, it helps reduce moisture loss from the soil surface, acts to reduce weed emergence and insulates the soil and grassroots from frost damage. In a healthy lawn the build-up of this dead material from lawn mowing clippings and naturally dying roots, shoots and leaves are balanced by the breakdown of the material by micro-organisms (bacteria and fungi), earthworms and other invertebrates. However, if the build-up of thatch is faster than the breakdown, the thatch layer gets too thick. Too much thatch can stop oxygen and moisture reaching the roots, and moisture trapped in the spongy thick thatch can encourage fungal disease of the lawn grass.
Keep Thatch in Moderation
You can help adjust the build-up of thatch by considering how you mow your lawn. Mulch mowing is when you leave the grass clippings on the lawn to break down, rather than collecting them in the mower catcher. Don't mulch when the grass has grown longer than 7 cm as too much will need cut off (never cut grass down by more than 1/3 of its height); instead, collect the clippings and compost them. Such long clippings would not easily get to the soil surface and would sit on top of the grass, smothering it. They would also take longer to break down, so the thatch builds up and becomes a moist mat where disease fungi and their spores can survive. Mulching lawnmowers cut up clippings to shorter lengths that will fall below the green grass leaves and are more easily broken down.
So, look at your lawn and examine the amount of thatch on the soil under the grass. If the soil is bare, set your mower to mulch and trim the lawn of 10-15 mm off the top. If the thatch is thicker than 5-10 mm then do not mulch and consider de-thatching by raking the thatch out using an Atlas Trade Scarifier Rake which is a sharp-tined rake that takes the thatch out of the lawn.
In early spring rake the grass, digging deep with the scarifier to penetrate the thatch and loosen it. Removing thatch by raking is best done in spring to prevent damaging the new grass growth.
Rake up the debris with a grass/leaf rake and place it in your compost heap or green waste and irrigate the lawn. It is then a good time to aerate your lawn by forking or using a coring machine. When the job is finished, the lawn will look roughed up, but don't panic. It will recover and eventually look better than before. It will take about 3-4 weeks for the lawn to recover and show signs of new growth. After aerating, over-seed and fertilise the lawn.