Each time you mow the lawn some of the cut grass is left behind. Some of this may be grass seeds as well as other organic matter. Thatch usually consists of grass clippings as well as living and dead grass particles. If allowed to get thick enough, this thatch layer begins to cut off water, sun and nutrients to the lawn. The result is that your lawn begins to take on a brownish complexion because it’s being starved by the thatch. Not only that, but insects move in and take up residence in the nice safe thatch. They then spread out and attack the lawn while spreading diseases that further undermine the condition of the grass. In time the thatch will become so thick that it may even interfere with the ability of the mower to do its job.