This is one that I've never had to deal with myself. But I've been asked this question an awful lot.
If my memory serves me correctly, in all cases where folks are struggling with that sort of thing, they haven't been mowing high, and their watering habits are not the best.
Can you describe what your mowing/watering/fertilizing habits have been like?
There's a hole in the bucket, dear Liza, dear Liza, a hole in the bucket, dear liza, a tiny ad:
Heat your home with the twigs that naturally fall of the trees in your yard