If your grass looks green on top and brown on the bottom, chances are your grass has thatch, unless it is the beginning of the growing season in early spring. Thatch is the dead clippings and debris near the ground that prevents the grass from growing full and lush. Thatch should be removed in the spring or fall every one to three years. After dethatching your grass, fertilize and water it with a lawn fertilizer specific to your type of grass.
Rent a dethatcher that has knives or blades (not tines) from a garden supply rental company to easily dethatch your lawn. Dethatchers are stand-alone machines or they can attach to a lawn mower; however, they can strain your mower's motor. If you have bentgrass, if possible, rent a dethatcher that has solid knife blades instead of flail type blade (as indicated on the label or by the rental store).
Set the blades 1/8 to 1/4 inch above the ground while the dethatcher is on a hard surface, such as a driveway or sidewalk. Most dethatcher blades are set by adjusting a lever or moving a bolt at each wheel.
Turn on the dethatcher (like a lawn mower) and go across your grass just as you would if you were mowing it. You may need to go over your lawn up to five times to effectively remove the thatch. Each time you start over, rake up the thatch, dispose of it and then make another pass in a different direction.
Dispose of thatch that was removed from grass where clopyralid, a weed killer, was used. Throw it in the trash; do not compost.