Thatch is that layer of dead grass and other naturally occurring debris that collects between the grass in your lawn and the soil. Too much thatch means you need to start using a dethatcher to remove the excess. How do you know when you have too much thatch? To check, cut a small plug out of your lawn and look at it from the side. If the spongy layer immediately under the grass is more than an inch thick, it is time to find a lawn dethatcher. You can find powered tools for removing excess thatch, but a dethatcher rake works just as well. Use the rake as you would any other, but make sure the tines get down to the soil. Then pull up slightly until you feel the thatch give way. The reliable sellers on eBay have every kind of dethatcher imaginable, from hand operated to battery powered for larger areas.