Lawn

Watering a lawn

A lawn in summer uses about an inch of water a week, more in heat and less in spring and fall. This guide covers how much to put down, how to tell when the lawn needs it, how long your sprinklers take to apply it, and how to keep it from running off. The Lawn Watering Calculator does the same math for your grass, climate and soil.

Updated October 2026 7 min read By Connor Schmitz

Weekly need

University of Minnesota Extension figures that a Minnesota lawn uses about 4 to 6 inches of water a month in June, July and August, and rain supplies about 3 to 4. Their advice is to add about 1 to 1½ inches a week in summer, minus any rain.

Colorado State University Extension gives a season-long schedule for cool-season lawns along the Front Range. Each figure is irrigation plus rain:

Time of year	Inches a week
Late April	0.75
May and June	1
July and August	1.5
September	1
Early October	0.75

CSU GardenNotes #265, Table 1.

Both are for cool-season grass in Minnesota and Colorado. Other climates and grasses need different amounts, and the calculator adjusts for both. A rain gauge or a straight-sided can on the lawn tells you how much rain to subtract.

Deep watering

UMN recommends wetting the soil to about 5 inches deep each time you water. From dry, that takes about ½ inch of water in sandy soil and up to 1½ inches in clay soil. Water past that depth drains below the roots.

To check, push a shovel in after a normal watering and pry the slot open to see how far down the soil is wet. Then step the soil back into place.

Between waterings, let the lawn tell you when it needs water. UMN lists three signs, and CSU uses the first two:

Color Gray-blue The lawn turns from its usual green to a grayish or bluish green.

Footprints Stay flat The grass doesn't spring back after you walk on it. CSU says footprints still visible an hour or more later mean it is time.

Wilting Slight wilt The blades start to wilt slightly.

Sunny slopes, south-facing spots and strips along sidewalks dry out first. UMN suggests hand watering those spots so the whole lawn can go longer between waterings.

Most common mistake

Watering a little every day. UMN notes that light, frequent watering grows shallow roots, while deep watering spaced as far apart as the lawn allows grows deeper roots that can reach more water. CSU recommends once a week in spring and fall and twice a week in summer for most Colorado soils.

Sprinkler rate

To turn inches into minutes, you need to know how fast your sprinklers put water down. That is the precipitation rate, in inches per hour. CSU gives typical rates for the two common kinds of in-ground heads:

How fast soil takes water in How fast sprinklers put it down

Inches per hour. Soil rates are FAO's basic infiltration rates for wet soil, converted from millimeters. Sprinkler rates are CSU's typical ranges.

A spray head at a typical 1½ inches an hour puts down ¼ inch in 10 minutes. A rotor at ½ inch an hour takes 30 minutes for the same ¼ inch. CSU warns against mixing spray heads and rotors in one zone, because they apply water at such different rates.

Ratings are only a starting point. CSU's catch-can test measures your own zone:

Step 1 Six cans Set six identical, straight-sided, flat-bottomed cans at random between the heads of one zone. Soup or vegetable cans work. Tuna cans are too shallow, and water splashes out.

Step 2 Ten minutes Run the zone for exactly ten minutes.

Step 3 One can Pour all six into one can and measure the depth with a ruler. That depth in inches is the zone's rate in inches per hour.

The pour works because six cans for one-sixth of an hour add up to one can for a full hour. If the cans held very different amounts before you poured them, a head may be broken or badly placed.

Try it

Turn a catch-can test into a run time

Can depth (in) Inches a week Times a week Heads

Rate1.50 in/hr

Each time20 min

Split2 × 10 min

Split into 2 runs with soak time between, so it soaks in instead of running off.

Run time per zone. The split follows CSU's Table 4 for runoff.

Quick check

After a ten-minute test, the six cans poured into one hold ½ inch. How long does the zone need to run each week for 1 inch?

Answer: 2 hours. Half an inch in the one can means the zone puts down ½ inch an hour, so 1 inch takes two hours. That rate is typical of rotors. Watering twice a week, that is 60 minutes each time, split into two 30-minute runs.

Lawn Watering Calculator Weekly water, days a week and minutes per zone for your grass, climate, soil and sprinklers, with cycle and soak when the soil needs it.

Open the calculator

Runoff

The chart above shows the problem. A wet clay soil takes in 0.2 inches an hour or less, and a spray head puts down 1 to 2½. On clay, compacted soil or a slope, water starts running off long before the session is done.

The fix is cycle and soak. Split each watering into shorter runs with time between them for the water to soak in. CSU suggests this many runs:

Run time	Spray	Rotors
1 run	Up to 16 min	Up to 48 min
2 runs	16 to 24 min	48 to 72 min
3 runs	Over 24 min	Over 72 min

CSU GardenNotes #265, Table 4.

On a controller, that means more than one start time. CSU notes that with only a few zones, the start times should be at least an hour apart. With a hose-end sprinkler, UMN's version is simpler: when water starts to puddle or run off, shut it off for 15 minutes, then finish.

Timing

UMN calls early morning, from about 4 to 8 a.m., the most efficient time to water. It is cooler, there is less sun and usually less wind, so less water is lost and the pattern is more even. Midday watering cools the grass but loses more to evaporation.

Avoid evening watering. Grass that goes into the night wet stays wet for hours, which can favor turf diseases. Where a city sets watering days or hours, those come first.

Dormancy

Watering all summer is a choice, not a requirement, for many lawns. UMN notes that Kentucky bluegrass left dry goes dormant. It turns brown and stops growing but usually does not die, and it greens up again when the weather cools and water returns. Fescues don't go dormant but grow slowly and use less water in dry spells.

Some grasses handle drought worse. UMN names perennial ryegrass and some improved Kentucky bluegrass varieties as less drought tolerant than older common bluegrass types. They also list cases where the lawn should be kept watered: turf recovering from disease, insects or heavy weeds, areas that get a lot of wear, and new seedings.

New seed is the exception to deep and infrequent. Seedlings have tiny roots, so they need light, frequent watering until they are established. The seeding guide covers that schedule.

Summary

Plan on about 1 to 1½ inches a week in summer, rain included, and less in spring and fall.
Water deeply, to about 5 inches, and wait for the gray-blue color or lingering footprints before watering again.
Find your zone's rate with six cans and ten minutes. The depth in the one can is inches per hour.
Spray heads put down water much faster than clay can take it in. Split long runs into cycles.
Water early in the morning and avoid the evening.

Sources

University extension services and the FAO.

Taylor, D., University of Minnesota Extension, "Watering Lawns and Other Turf" ↗, FS-02364-A (reviewed 1998). Summer water use and the 1 to 1½ inch figure, the 5-inch depth, the shovel check, signs of water need, timing, runoff pauses and dormancy.
Whiting, D. and Jones, K.M., Colorado State University Extension, "Methods to Schedule Home Lawn Irrigation" ↗, GardenNotes #265. The seasonal schedule, the catch-can test, cycle and soak, and signs of water stress.
Colorado State University Extension, Colorado Master Gardener, "Sprinkler Types Used for Lawn Irrigation" ↗. Precipitation rates for spray heads and rotors.
FAO, Irrigation Water Management, Training Manual No. 1, Table 7 ↗. Basic infiltration rates by soil type.

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