Established lawns and landscapes need not be watered daily. Deep, infrequent irrigation is better than frequent sprinklings. Two irrigations per week are usually sufficient except during extremely hot, windy periods.
Unless the irrigation system is calibrated, even an experienced gardener might not know how much water is being applied. Since no two irrigation systems are the same, each one should be calibrated in order to determine the exact amount of water that is being applied. Established lawns and shrubs, on sandy sites, should be given ½ to ¾ inch of water at each irrigation.
Find out how much water your system is delivering and make any necessary adjustments. Placing 5 to 10 straight-sided cans or pans at random throughout the area to be irrigated can easily do this. Run the system a predetermined amount of time and, using a ruler, check the depth within the cans/pans. Continue to check the cans/pans and keep up with the sprinkling time until an average of one half inch is collected in the containers.
Doing this test may reveal that only a fraction of what is needed is being delivered. On the other hand, the system is sometimes found to be delivering excessive amounts of water which is wasted.
Some homeowners say that no matter how much they water, certain spots in the lawn seem to wilt soon after irrigation. Wilted spots in lawns (those light gray, sickly looking areas) show up more frequently during periods with little to no rainfall. To solve this problem, first check to see if your sprinkler pattern is overlapping properly and providing uniform coverage. This can be done using cans/pans, as described above.
A second cause could be differing soil textures within the lawn. Sometimes differing textures of soil are used for filling different areas during construction. The more sandy or porous areas become dry more quickly. Consider watering these areas with spot watering sprinklers between regular irrigation times, instead of watering the entire lawn.
A third cause could be a compromised lawn root system. This can be caused by a soil-borne pest. Examples include nematodes (microscopic roundworms) that feed on the root system, ground pearls (scale type insects) that live in the soil and feed on lawn roots, grubs (larval stage of various beetles) that feed on roots or a root fungus. These types of pests injure/kill the lawn’s root system, resulting in the roots not being able to take up adequate amounts of water and nutrients. Diagnosing soil dwelling pests can be difficult, requiring some expertise and sometimes requiring the submission of an appropriate sample to a diagnostic lab.