Don't let your lawn suffocate under a matted layer of dead vegetation. A lawn thatcher, when used properly, will pull the thatch and leave the grass on its way to excellent health.
Moss is familiar to everyone living in the Pacific Northwest. It will crowd out lawn grasses, and it grows best when 3 conditions are met: moist ground, shade, and a pH of about 6.2.
Ferrous sulfate to kill moss, plug aerate, dethatch, appropriate fertilizer, soil sweetener, and clay modifier are fairly regularly called for on Vancouver, Washington lawns.