Hello, I need help. Two years ago I cut three large maple trees in my back yard. The stumps were ground below grade but the guy left all the chips in the hole. I dug out the chips to about 6" and backfilled with a compost and loom mix. Added starter fertilizer and Pennington grass seed. Not much grass grew, just splotches here and there. I just can't grow grass where the trees were. What am I doing wrong? Help!