Whether you have a sandy or clay soil will have a huge influence on the watering practices for your lawn. Sandy soils do not hold very much water and, therefore, lawns growing in sandy soils will need to be watered more frequently. The grass will still use the same amount of water per week, but if the soil cannot hold very much water, you will need to irrigate more frequently. Loamy and clay soils can hold more water than sandy ones and, therefore, lawns growing in clay type soils will not need to be irrigated quite as often.
In either case, apply enough water to penetrate the soil to the depth of the grass roots. Use a shovel or soil probe to determine rooting depth. For most clay type soils it may take 1 to 1¼ inches of water to fill the soil to a depth of 12 inches. For sandy soils, only ¼ – ¾ inch of water is all that may be necessary to fill the soil to a depth of 12 inches. Use a screwdriver to check moisture depth. The screwdriver should easily penetrate the soil to the desired depth you want the water.
In sloped areas, lawns with heavy thatch, or lawns growing in clay or compacted soils, water may need to be applied in small amounts separated by one-half hour increments to allow for adequate water infiltration and to prevent run-off.