Over time, some of those roots decay, causing thatch — a layer of dead material. If allowed to grow thicker than half an inch, thatch can choke a lawn of water and air and slowly strangle your lawn like some sort of invisible boa constrictor.
To help control thatch, apply a mid-summer feed of Jonathan Green’s “Natural Beauty” all organic fertilizer which is fortified with humates to help restore soil life.
Mechanical dethatching is best done in mid to late September. Also, try raking a quarter inch of top-dressing soil over your lawn, which can accelerate the thatch’s decay rate. But don’t overdo it and try to eradicate all the thatch since a thin layer actually protects the roots beneath it.