Thatch is a layer of dead plant material that resides at the soil level. It is comprised of old grass clippings and other matter that has not decayed back into the soil. While a small amount of thatch is normal in an organically active and healthy lawn, an elevated layer on the surface of the soil will deprive the lawn of much needed oxygen, water, and nutrients. Adding organic matter to your soil can relieve the choking effects of thatch. Additionally, lawn aeration, the application of Compost Tea followed by the application of Organic fertilizers are a positive and lasting approach to combating thatch.