Follow these tips for a crash course in watering a lawn.
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Most lawns need between 1" and 2" of water per week in middle of summer, depending on the temperature. In some areas, rainfall will provide most of the water needed. In drier areas, watering is a weekly obligation.
Before you can determine how long you should water your lawn, you need to know how much water your sprinklers apply. To find out, conduct a can test. Set five straight-sided, flat-bottomed cans (tall cans may not be appropriate, as the water could bounce off them, so tuna-type cans work best) or cups randomly on your lawn. Run the sprinklers for a set time (15 or 30 minutes works well), then measure the amount of water in each container. Use the average to determine how long to water. (For example, if your lawn needs 1-1/2" of water a week and the sprinklers put out an inch in 30 minutes, you need to run them for a total of 90 minutes a week.) In most areas, the total amount of water applied is broken up into two applications per week.
Adjust your sprinkler system so that water levels in all cans are equal.
Dry areas may require more water.
To fine-tune your lawn watering, use evapotranspiration (ET) guidelines to determine how much water to apply. ET is the amount of water that transpires -- or evaporates as waste-containing vapor -- from plant leaves combined with the amount of water that evaporates from the ground. Using historical weather data from your area and scientifically determined ET rates for lawn grasses, you can determine precisely how much water your lawn needs. Contact your local water department to see whether ET watering guidelines are available for your area.
Because the entire root zone should be watered thoroughly, the water should penetrate 6" to 8" into the soil. To check the depth of moisture, insert a rod or screwdriver into the soil; it will stop when it reaches dry dirt.
Water your lawn early in the morning.
Check your sprinkling system for repairs or adjustments.
Pulse irrigate (turn the water on for a while and let the water soak in, then turn it off, then repeat the sequence) if you have a sloping lawn.