Dethatching a lawn can be a long, difficult process requiring laborious raking and cutting to remove the thatch at the base of the blades of grass. Thatch is made up of the dead grass that has fallen down between the living stems and become entangled. If left uncontrolled, thatch will choke out the lawn and leave a brown, dry mess.
When dead grass stems and clippings become intertwined with the living grass stems it forms into thatch. It acts as a natural insulator and protector of the soil around the grass roots and stems. Grass develops thatch naturally, and over time the grass and thatch work into a balance that is beneficial for the health of the lawn if no external factors are introduced into the ecosystem.
Thatch is meant to decompose slowly and reintroduce the nutrients of the dead grass stems into the soil at the base of the living grass. Healthy colonies of microbes devour the dead grass stems and excrete the essential nutrients in a form that can be reabsorbed by the roots of the lawn. Excessive thatch is a sign that decomposition isn't occurring at a normal rate for some reason.
Adding fertilizer to your lawn adds nutrients to the soil that promote growth and greenness, but the problem is the microbes don't have enough food to eat to survive, so they die off and when the grass is cut and dies there aren't enough microbes to digest it before more dead grass falls on top. This makes the thatch layer continue to grow in thickness until it can threaten the life of the grass that caused it in the first place. Fertilizer creates an imbalance in the lawn ecosystem that needs to be rectified at some point.
Mix 4 parts beer to 2 parts dish soap to 1 part ammonia. Use a hose spray attachment that will dilute your mixture with 20 gallons of water, and spray it over your entire lawn. The beer contains sugars, yeast and enzymes that feed the colonies of microbes in your lawn and help them to regain their numbers so they can begin digesting the thatch. Repeat this process monthly during the growing season for your lawn. At the end of the season use dethatching rakes or a dethatching machine to remove the remainder of the thatch that hasn't been devoured by the microbes.