At this stage, the lawn color appears to change from a bright green to a dull blue-green or smoky color. You are actually seeing the bottoms of the wilted blades, which are grayer than the tops. The first occurs in the most drought-prone spots, especially beneath trees. It is best to soak the soil deeply and then not water again until the top inch or two of soil begins to dry. Too much watering can quickly leach fertilizers and nutrients from around the root zone, and can make the grass grow faster and need more frequent mowing.
Constant moisture can also promote weed growth and diseases.
On the other hand, if a lawn is not watered enough, its roots will remain shallow and thus unable to make use of water that penetrates further into the soil. To keep grass roots growing deeply, it is important to moisten the soil to a depth of 6 to 12 inches. For most soils and lawns, it is best to divide the application into two or three installments. Doing this prevents wasteful runoff by allowing the water to soak in more slowly.