Thatch is a layer of roots, weeds, seeds, grasses, and other debris that can destroy the health of your lawn. When thatch builds up underneath your lawn, it limits the ability for your lawn to derive the nutrients that it needs. The best way to maintain the health of your lawn is to remove thatch, a process known as dethatching your lawn. Certain types of grasses may be more prone to developing thatch. Also, when grass clippings are left on the lawn after mowing, it is possible that the clippings can contribute to thatch build up. Thatch also appears more frequently in lawns that have never been aerated.
Your lawn's soil should be soft enough that you can easily slide a twig or small stick into the soil without needing force. If you find that you need to force a small twig into the soil, then chances are you have a strong thatch build up, that will continue to accumulate and threaten the health of your lawn. Some other signs that your lawn may need to be dethatched include slow draining, noticing that it takes a long time for new growth, or if your soil turns brown very quickly.