The average lawn size in the U.S. is about 1/5 of an acre, or a little less than 9,000 square feet, and it takes at least 624 gallons of water to apply 1″ of water on 1,000 square feet of lawn. It thus takes a total of more than 67,000 gallons to apply 1″ of water per week to an average lawn for three months during one summer. Even if you only halve that amount by allowing your lawn to go dormant, you’re still conserving a tremendous amount of water–enough water to supply a family of three’s drinking water requirements for 61 years. Whether you want to help conserve water or you just don’t have time to water your lawn regularly, letting your grass go dormant during the hottest months of the year can help. A dormant, or “sleeping,” lawn will turn brown, but with proper care the underground crown of the grass plant will survive. In fact, once the grass receives ample water again (either from natural precipitation or from a sprinkler), it will begin to green up and grow new leaves. This makes sleeping lawns a great choice for climates with mild winters, where you can enjoy a lush, green lawn for most of the year while drastically reducing your lawn’s summer water demands.
Grow drought-tolerant grasses. Most grasses commonly used in lawns can withstand periods of dormancy quite well, but some are better than others. Buffalo grass, zoysia grass, fine-leaf fescues, tall fescues, and older, “common” varieties of Kentucky bluegrass (in that order) are the most tolerant of drought stress. Perennial ryegrass and newer, “improved” varieties of bluegrass require more water to keep the dormant plants alive. The more drought-tolerant your grass, the longer it will stay green without watering, and the less you’ll have to water it to keep it alive while it’s dormant.
Make sure your lawn is healthy. Newly sodded or seeded lawns should not be allowed to go dormant, as they are not well enough established to survive drought conditions. In addition, grass with excessive thatch buildup, grass that has been damaged by insects or disease, or lawns in poor soil generally do not tolerate drought-induced dormancy well. In all these cases, you should water your lawn regularly to keep it green.
Keep your mower blade high. When the grass is still green and growing in the spring, mow with a sharp blade set at a height of 3″ to 3-1/2″ (7.6 – 8.9 cm). Allowing your grass to grow relatively high like this will increase its drought tolerance. As a result, the lawn will stay green longer before going dormant.
Allow your grass to go to sleep. In areas with mild winters, grass may be green all winter long, while in other areas it will come out of winter dormancy and green up with increasing spring temperatures and rainfall. As long as there is adequate rainfall, your grass will stay green without you having to water it. When precipitation decreases and/or temperatures increase, the lawn will turn brown and go dormant unless you water it. At this point, you can stop watering at any time to allow the grass to go to sleep. Once you stop watering, you can generally allow the more drought-tolerant varieties above to go up to 4-6 weeks without water before you need to water again. Rye grass and newer varieties of bluegrass generally shouldn’t go more than two weeks without water.
Understand a dormant lawn’s water needs. Dormancy is the grass plant’s natural response to survive periods of inadequate water. If the dormant lawn goes several weeks or a month without water, though, it typically will not recover, even when thoroughly watered later. The exact amount of water you will need to give your sleeping lawn needs depends on the temperatures, the humidity, and the amount of precipitation it receives naturally, but as a rule of thumb you should apply at least 1/2″ (1,27 cm) of water after the initial 4-6 weeks of drought. You should then apply at least 1/2″ (1,27 cm) of water every 2-3 weeks thereafter for as long as drought continues. If your summers are particularly hot and dry, as they are in the desert areas of the southwest U.S., for example, most grasses will require more water than this to survive. Buffalo grass and zoysia grass, however, generally require less water than bluegrass and fescue, and rye grass requires up to twice as much. Note that these waterings are only intended to keep the underground portions of the plant alive, and you typically won’t notice any greening of the lawn above ground.
Measure precipitation. Get or make a rain gauge to determine how much precipitation your lawn is getting, and keep track of this precipitation. Don’t rely on your local weather reports, because these may not accurately measure the amount of rain that actually fell on your lawn.
Water the lawn enough to keep the grass alive. While you should make sure your sleeping lawn gets at least 1/2″ (1,27 cm) of water every 2-3 weeks (as stated above), this doesn’t necessarily mean you have to water it that much. If your lawn is already receiving that much rainfall (as measured by your rain gauge), you don’t have to water the grass at all. You only need to water enough to make up for any difference between your lawn’s needs and the natural precipitation it receives.
• Regular irrigation, as described above, is less important for some types of grass than for others. Lawns composed of buffalo grass, wheat grass, Bermuda grass, zoysia grass, and older varieties of bluegrass, for example, can sometimes endure months without any water and still fully recover. Fescues, if left not watered for long periods, may also recover fully, but they often exhibit thinning or develop bare patches, while perennial rye grass is likely to emerge from dormancy a bit spotty even with regular watering.
• It’s best to check with your local extension service or water conservation agency to determine the exact water needs for your particular variety of grass in your local climate.
• Select grass varieties that are appropriate for your climate and setting. While zoysia grass, for instance, is remarkably drought-tolerant, it generally doesn’t do well in more northerly climates, and it requires ample sunlight.
• If you live in an area where you can grow Buffalo grass and zoysia grass, consider that you can typically keep these grasses green with as much or less water than it takes to keep dormant bluegrass or rye grass alive.
• Check to make sure your soil has adequate potassium. Adding potassium in the spring and summer will make your lawn more drought-tolerant. Do not add nitrogen in spring or summer, however, as this will have the opposite effect.
• Grass that goes dormant in the winter will also benefit from occasional watering if dry conditions persist for several weeks. By providing the dormant lawn with enough water to keep the grass plants’ crowns alive, you can fend off problems with thinning or poor recovery in the spring. Don’t water, however, when the temperature is below 40°F (10°C).
Information Source: http://www.wikihow.com/Save-Water-with-a-Sleeping-Lawn