Thatch is the dense spongy layer at the base of your lawn made up of tightly interwoven or compacted stems, leaves and roots. Lawns with high levels of thatch (2 cm or more) can create an environment in which disease and pest insects thrive. Poor drainage, compacted soil and unfavourable pH can contribute to high levels of thatch. D-Thatch will de thatch the lawn by organically boosting the decomposition of thatch gradually over approximately one month.