How Long Should You Water Your Lawn? Minutes, Gallons and the Can Test
Most lawns need about 1 to 1.5 inches of water a week in the growing season, rain included. How long that takes depends on your sprinkler: a spray head puts down about 1.5 to 2 inches an hour, so 1 inch takes 30 to 40 minutes, while a rotor puts down about half an inch an hour and needs about two hours. Water two or three times a week rather than a little every day.
How much water is an inch?
An inch of water over one square foot is 144 cubic inches, which is 0.623 US gallons. So a lawn needs about 0.623 gallons per square foot for each inch.
| Lawn size | 1 inch a week | 1.5 inches a week |
|---|---|---|
| 1,000 ft² | 623 gallons | 935 gallons |
| 2,500 ft² | 1,558 gallons | 2,338 gallons |
| 5,000 ft² | 3,117 gallons | 4,675 gallons |
| 7,500 ft² | 4,675 gallons | 7,013 gallons |
| 10,000 ft² | 6,234 gallons | 9,351 gallons |
Step 1: Find out what your sprinkler puts down
The number to know is your sprinkler's precipitation rate in inches per hour. Do the can test:
- Put out 5 or 6 straight-sided cans (tuna cans work) at different distances from the sprinkler.
- Run the sprinkler for 15 minutes.
- Measure the depth of water in each can with a ruler, and take the average.
- Multiply the average depth in inches by 4 to get inches per hour.
If you know the sprinkler's flow, a quicker way is rate = 96.25 × gallons per minute ÷ the area it covers in square feet. A sprinkler using 4 gallons a minute on 400 ft² is putting down 96.25 × 4 ÷ 400 = 0.96 inches an hour.
Step 2: Work out the run time
Minutes per watering, for common sprinkler outputs:
| Sprinkler output | Typical for | 1 inch a week, 2 times | 1 inch a week, 3 times | 1.5 inches a week, 3 times |
|---|---|---|---|---|
| 0.5 in/hour | Rotor / gear-driven sprinkler | 60 min | 40 min | 60 min |
| 1 in/hour | Impact or oscillating sprinkler | 30 min | 20 min | 30 min |
| 1.5 in/hour | Fixed spray heads | 20 min | 13 min | 20 min |
| 2 in/hour | Fixed spray heads (high output) | 15 min | 10 min | 15 min |
Enter your own lawn, rate and target in the lawn watering calculator, which also gives the gallons and the cost on your water bill.
When and how often
- Early morning. Water before about 10 am, when it is cool and calm. Less is lost to evaporation and wind, and the grass dries through the day. Evening watering leaves the grass wet overnight, which favors disease.
- Deeply, not daily. Two or three long waterings a week soak the soil and push the roots down, which makes the lawn tougher in a dry spell. Short, daily watering keeps the roots shallow.
- Count the rain. A rain gauge shows what the sky provided. Skip a watering after a good soaking.
- Cool-season and warm-season grasses differ. Cool-season grass (fescue, bluegrass, ryegrass) peaks in spring and fall and goes dormant in a summer drought. Warm-season grass (Bermuda, zoysia) grows in summer heat, and needs less water.
If water runs off
On slopes and hard clay soil, water runs off before it soaks in, especially with a high-output spray head. Split the watering into two or three short cycles about an hour apart, so that the first soaks in before the next arrives. A rotor, which puts down water slowly, is often a better match for these areas.
Signs the lawn needs water
- The grass turns a dull blue-gray instead of bright green.
- Footprints stay flattened and do not spring back.
- A screwdriver pushed into the soil meets hard dry ground below the first inch or two.
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