Your grass might be as short as a putting green, but don't keep it that way. Let it grow to a length of about 3 to 3½ inches, and maintain that height all season. This lets the grass blades shade out weed seeds, and in the summer it shades the soil, reducing evaporation. Come fall, you can go back to cutting it short—weed seeds aren't as abundant then, and evaporation is less of a concern. Two exceptions are Bermuda and seashore paspalum grasses, found in the South, which can be kept at a height of 3/4 to 1 inch.