Each watering should moisten the soil to a minimum depth of 6 inches on grasses. This is the grass's active root zone. The length of time and amount of water it will take to moisten the root zone depend on soil type and the irrigation system. Water will penetrate sandy soils more quickly and more deeply than clay soils. To determine the length of time required to moisten your lawn's root zone:
- Run the sprinklers for 15 minutes.
- Twenty-four hours later, dig a small hole in the ground or use a probe to determine how deeply the soil is moistened. You will use this information to determine how long to water each time.
- To calculate the number of minutes to water the lawn divide 120 by the depth of the moistened soil in inches. For example, if the water soaked in 4 in., figure 120/4 = 30 minutes. It would take an hour to soak in eight inches. If it soaked in 6 in., the lawn should be watered for 20 minutes (120/6 in. = 20 minutes). However, bluegrass has a shallower root system than other grasses; it needs to be soaked to a depth of only 6-8 in. (instead of 8-12 in). Take the second example above: In 15 minutes, water soaked in 6 in. You would need to water a bluegrass lawn for only 15 minutes instead of the 20 minutes calculated for other types of grass.
Once the length of the watering period is established, use the same period each time you water, no matter what the season. If water starts to run off the lawn before the end of the watering period, turn the water off for one hour and let the water soak in; then turn the sprinklers back on and finish watering. You should also apply LazyMan Soil Doctor to aerate the soil and break down thatch. This will help your water penetrate down deeper.
How often you water will change with the seasons and soil type. First determine how much water is applied during your watering period. Set straight-sided containers like cans around the lawn and turn on the sprinklers for your usual watering period. At the end of the watering period, measure the amount of water in each of the cans. (If the depths vary widely, the sprinkler system needs adjustment. Adjust or replace the sprinkler heads as described below to get more uniform application, then do the can test again). Use the average amount of water in the cans to determine watering frequency.
In the hottest part of the summer, bluegrass will use 1/4 - 1/3 inch of water per day. Bermuda grass can be maintained on 1/5 - 1/6 inch although it will use more if more is applied. If your watering period is 30 minutes on a bluegrass lawn and you apply 1 inch each time, you need to water once every 3 days in the hottest part of the summer. If you are applying more water during each watering, water less often. Avoid frequent, shallow watering. It encourages a shallow root system, which makes the lawn more susceptible to drought and grub damage. If you are watering your lawn more than three times per week consider soil modification, a different grass species, or a change in management practices. In spring and fall, water less frequently but for the same period of time.