The question of how long to run a lawn sprinkler does not have a simple, universal answer. Determining the correct duration involves measuring your system’s output and performing a calculation based on your lawn’s needs. Setting a proper watering schedule is important for maintaining a healthy lawn and practicing water conservation. The correct duration ensures water penetrates the soil to a sufficient depth, which is more beneficial than applying a small amount of water every day.
The Purpose of Deep, Infrequent Watering
The primary goal of watering is to encourage grass roots to grow deeply into the soil. Brief, frequent watering leaves moisture only in the top inch or two, forcing roots to stay near the surface. This results in a shallow, weak root system highly susceptible to stress and browning during hot or dry conditions.
A deep watering session saturates the soil to a depth of six to eight inches, the typical root zone for established turfgrass. This action pulls the roots downward, creating a robust, extensive structure. Deeply rooted grass is more resilient to heat and drought and can better access nutrients. Allowing the soil surface to dry out slightly between deep watering events also helps prevent certain turf diseases.
How to Measure Sprinkler Output
Before calculating the run time, you must determine your sprinkler system’s water application rate. Find this rate by conducting a simple “catch-can” test. Place several short, straight-sided containers, such as tuna or cat food cans, randomly across the lawn area served by one sprinkler zone. Ensure the cans are positioned near the sprinkler head and the edge of its spray pattern to capture an accurate average.
Run the sprinkler system for a fixed duration, such as 15 minutes. Use a ruler to measure the depth of water collected in each can. Calculate the average depth by adding all measurements and dividing by the number of cans used. To find the application rate in inches per hour, multiply this 15-minute average by four, since there are four 15-minute intervals in one hour.
Calculating the Minutes to Run
The final calculation for run time combines your system’s output rate with the amount of water your lawn requires. Most turfgrass needs one to one and a half inches of water per week, but this depth must be adjusted based on soil type. Heavy clay soils hold water well, benefiting from a single, deep application of about one inch. Sandy soils drain quickly, requiring smaller, more frequent applications, such as one-third of an inch three times per week.
To convert the required inches of water into the exact minutes your sprinkler must run, use this formula: Run Time (minutes) = [Amount of Water Desired (inches) ÷ Application Rate (inches/hour)] x 60. For example, if your application rate is 0.5 inches per hour and you want to deliver 1 inch of water, the calculation results in a 120-minute total run time. On heavier soils, this long duration may need to be broken into two or three shorter cycles with rest periods to prevent runoff, a process known as “cycle and soak.”
Frequency and Time of Day
The correct duration must be paired with an appropriate frequency to maintain a healthy lawn. The deep watering method requires running sprinklers only two to three times per week, depending on climate and soil type. This infrequent schedule encourages the deep root growth necessary for drought tolerance.
The best time to water is during the early morning hours, typically between 4 a.m. and 10 a.m. Watering then allows moisture to soak deeply before the heat of the day causes significant evaporation. Morning timing also ensures grass blades dry completely before nightfall. Prolonged moisture on the leaves overnight creates an environment conducive to fungal diseases, so late evening watering should be avoided.