  Great lawns aren't made; they're grown. And it's up to you to
keep them that way by watering and fertilizing—the two
maintenance chores that separate okay lawns from truly great
ones.  When to Water Your lawn will let you know when it needs
water: As blades of grass curl lengthwise to conserve moisture,
the grass loses its green luster and turns a blue-gray color.
Your lawn will also lose its ability to bounce back when you
walk on it, and it may develop brownish patches. These signs
appear very fast during hot, dry weather, so keep your eyes open
for them.     How Much to Water  If you water your lawn only a
little bit every three or four days, the roots will be shallow,
because the water only penetrates the top of the soil. When the
hot, dry summer weather comes, shallow-rooted lawns won't be
able to extract moisture from deep in the soil. If you over-
water, on the other hand, the water will go farther down into
the soil than the roots need, and you'll waste water and
possibly kill the grass by depriving