i do alot of thatching in spring and fall, this year especially. i have a client who had us there to thatch and seed 3 yrs ago, lawn looked great. this spring he had us there to thatch, and hired us for fert program too. his lawn looked great all season, and still does, but there is considerable thatch build up again. we are gonna thatch again, y the heck does it keep coming back? what causes it?