Solved! How Long to Water Your Lawn
Encourage the growth of lush green grass with this foolproof formula for running your sprinklers.
Q: The brown grass in my yard seems to indicate that I’m under-watering it. How long should I run my sprinklers when I water the lawn?
A: A sprinkler system can water your lawn evenly, efficiently, and effortlessly, but the health of your turf depends on how long you run it. Under-water by running your sprinklers too briefly and the grass will curl up and brown; overwater by leaving sprinklers on too long and the soggy ground will invite excess thatch, pests, and/or fungus while wasted water will run off and weather your hardscape. The ideal watering duration for your lawn depends on a variety of factors, including grass type, season, sprinkler system, and weather. Read on to learn exactly how long to water your lawn for a healthy, vibrant turf.
Determine your lawn’s weekly watering needs.
First, learn how much water, in inches, your lawn needs a week. Most require an average of one to 1½ inches weekly, but specific watering needs vary by turfgrass type (cool season versus warm season) and time of year (active versus dormant growth season). Check with your local Cooperative Extension Service office for precise weekly watering recommendations.
In general, cool-season grasses need more water than warm-season grasses, and watering needs are higher in the active season (spring and fall for cool-season grass, mid- to late spring through early fall for warm-season) than in the dormant season (winter for cool-season and warm-season). Cool-season Kentucky Bluegrass, for example, needs 1½ to two inches per week in the active season and ½-inch per week in the dormant season. In contrast, warm-season Bermudagrass needs only one to ¼ inches of water weekly in the active season and only ⅛ inches per week in the dormant season.
Figure the water output of your sprinkler system.
To calculate how much water your sprinkler system puts out per hour, place six straight-sided containers of the same size and shape in one area of the lawn where your sprinklers hit and run your sprinklers for 20 minutes. Measure the depth of water (in inches) in each container with a ruler and calculate the average depth across the containers. Multiply the depth by three to figure out how many inches of water your sprinkler system outputs per hour. For example, if the containers each had ⅓, ¼, ¼, ¼, ¼, and ⅕ inches of water, the average water depth would be ¼ inches, and your sprinkler’s water output would be 1½ inches per hour (¼ X 6).
Calculate how long to water the lawn with your sprinklers each week.
To figure out how long your sprinklers should run each week, divide your lawn’s weekly watering needs in inches by your sprinkler’s hourly water output. For example, if your Bermudagrass lawn needs one inch of water weekly, and your sprinkler’s water output is 1½ inches per hour, you would need to run your sprinklers for ⅔ hours, or about 40 minutes per week on average (1 / 1½).
Divide weekly sprinkler duration by weekly watering frequency to calculate how long to run your sprinklers each watering session.
To grow a healthy lawn, water must reach and be fully absorbed by the grass roots, which requires watering often enough to suit your lawn’s soil type. If you water only once a week, you could wind up with soggy soil that invites pests and rot. Water daily, and the water may only reach the top of roots, yielding short roots and a dry turf.
In general, clay and loamy soil store water longer but absorb it more slowly, so water lawns with these soil types one to three times per week. Sandy soil absorbs water faster but doesn’t store it as long, so water two to four times weekly.
To determine how long to run your sprinklers during each watering session, divide the total weekly sprinkler duration by the weekly watering frequency. If you need to run your sprinklers 40 minutes per week to meet your watering needs, and plan to water your lawn twice a week, set your sprinkler to run for 20 minutes each watering session (40 divided by two). Space watering sessions at least a few days apart to allow the grass roots to absorb water and breathe.
Adjust the math to account for rainfall.
The above calculation will tell you how long to run your sprinklers in an average week with no rainfall. But natural rainfall reduces the need for supplemental irrigation. To figure out how long to water your lawn during a week when it rains, subtract the number of inches of rainfall from the weekly watering need to get your new weekly watering figure and do the rest of the calculations normally. So if your normal weekly watering need is one inch of water, but you get a half-inch of rain one week (as measured with a rain measurement tool known as a rain gauge, which you can pick up on Amazon), your watering needs for that week are only half an inch of water. If your sprinkler output is 1½ inches per week, your sprinklers should run for only ⅓ hours or 20 minutes that week (½ divided by 1½). On a twice-weekly watering schedule, run your sprinklers 10 minutes each time.