This Is the Best Time to Water Your Grass, According to a Lawn-Care Pro

“The absolute best time to water your lawn is the early morning, before 10 a.m.,” Maurer tells Popular Mechanics. Cooler temperatures and calm breezes help keep evaporation to a minimum. And watering in the morning keeps the turf cooler during the hottest parts of the day, which means less stress on the grass.

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If it’s not convenient to water in the morning, late afternoon is the next-best time. However, don’t wait too long. Although it might seem smart to wait until nighttime, when temperatures are cooler, watering in the evening keeps lawns wet overnight, which can make the grass susceptible to disease. “My pet peeve is when people water at six o’clock or later in the evening,” Maurer says. “A wet lawn at night is the perfect condition for fungus to grow. Along with cutting grass too short, watering at night is about the worst thing you can do to a lawn.”

As a general rule, you should water long enough to moisten the soil down to about 6 inches, which is the average depth of a healthy grass-root system. It takes about one inch of water to properly hydrate normal lawns to that depth. But, Maurer warns, “each lawn has different soil. You have to water for your specific property.”

There are a few ways to determine whether your lawn is getting the right amount of water.

The simplest way to determine if the soil is properly watered is to conduct the screwdriver test. After watering the lawn, take a long-blade screwdriver and shove it straight down into the lawn. The blade should easily penetrate the soil to a depth of 6 inches. If it doesn’t, the soil is hard and dry, and you’re not watering enough. You can also use a shovel to lift the sod and dig down 6 inches, but the screwdriver test is easier on the lawn.

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If you just bought a new sprinkler, calculate its flow rate to determine precisely how much water is being sprayed onto the lawn. Multiply the square footage of your lawn by 0.62 gallons; that’s the amount needed to reach one inch of water per square foot. Then, divide by your sprinkler’s flow rate to determine how long to water.

Don’t know your sprinkler’s flow rate? No worries. Just set out an empty can in the watering zone, and time how long it takes for the can to fill 1 inch deep with water.

An in-ground irrigation system with pop-up sprinkler heads is the best way to water lawns. The timer automatically waters the lawn at preset times, and delivers a precise amount of water for your particular lawn. “In-ground sprinklers are the most efficient way to water lawns and will pay for [themselves] in the long run,” Maurer explains. “Over the years, if you’re planning on staying in your house, an irrigation system is a worthwhile investment.”

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But for homeowners who don’t have an in-ground irrigation system, or don’t want to invest in one, Maurer suggests using a pulsating, revolving sprinkler hooked up to a garden hose. “This is the next best choice for watering an established lawn,” says Maurer. (For watering a new lawn, see the next tip.) Pulsating sprinklers shoot out water horizontally at high velocity, so it’s not as vulnerable to wind and evaporation as oscillating types, which spray the water straight up, and then rotate side to side.

There are two basic types of pulsating sprinklers. The first type has a wide, flat base that sits on the grass and can easily be moved around the yard. The second type of pulsating sprinkler is attached to a sharp spike that allows you to stick it into the ground anywhere on the property.

How often you should water a lawn is dependent on several factors, including the type of soil. Maurer recommends watering clay soils once a week, and sandy soils about every three days. “People think they need to water the lawn as frequently as their landscape plants. They want to water for 15 minutes every single day,” he says. “Be careful not to over-water. Most people think more water is better, but it’s not.”

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Conversely, too frequent or very light watering can lead to fungus growth and a shallow root system that can’t support the grass. Watering that soaks the soil more deeply encourages the roots to grow deeper and stronger. “You want to train the roots to go down deep into the soil with proper watering,” Maurer says. “I tell my customers if you’re going to water, water every three to seven days once we hit summer. And if you see mushrooms sprouting in your lawn, you’re probably watering too much.”

A very common lawn-watering practice is to turn on the sprinkler and then watch the clock and try to remember to turn off the water. What happens all too often, however, is that you get involved in something else and completely forget that the sprinkler is running, and you end up wasting water and over-saturating the lawn. Here’s a better option: buy an automatic lawn-sprinkler timer.

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The timer screws onto the hose bib (spigot) outside your house, and then the garden hose connects to the timer. “With a timer, you don’t have to ever worry about remembering to turn off the sprinkler,” Maurer says, “the timer will automatically shut off the water after a preset amount of time, ensuring the lawn gets the proper amount of water.” Some timers also measure flow rate, so you can get an accurate idea of exactly how much water your lawn needs to stay green and lush.

Lawns in new housing developments, where the topsoil was removed, often have soil so hard that water can’t sink in.

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In that case, homeowners need to water in stages to soften up the ground so water can eventually seep down into the soil. “Water for 30 minutes, then stop and let the water soak into the ground. Then, water for another 30 minutes,” Maurer says. Don’t try to water all at once; compacted soil can only absorb so much water in 30 minutes. After that, the rest of the water will simply run off.

Pulsating sprinklers work great for lawns with mature grass, but for newly planted lawns, the intense water stream can wash away the seeds and erode soil. Oscillating sprinklers are a better, gentler choice for new lawns until the grass takes root.

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“Oscillating is good for new grass and for recently sown grass seed. The water is not too strong to push the seed, and the water stream is softer when it lands,” Maurer says. For newly planted grass seed, keep the top inch of the soil moist, but not soggy. Monitor and water regularly until the grass is 3 inches high, then water on your regular cycle. Also, be very careful when mowing not to damage the tender grass. Take wide, slow turns to prevent the mower’s wheels from tearing up the lawn.

“If you’ve just planted sod, water for 15 minutes everyday for the first two weeks, or twice a day during very hot weather,” suggests Maurer, “and occasionally walk along the seams between the sod pieces to gently press the sod down into the soil and help the roots to knit.”

“If homeowners don’t want to water their lawn, that’s fine,” Maurer says. The lawn will go dormant just as it does in the winter, which won’t harm the grass as long as there’s not a drought lasting longer than a month. However, if you let the lawn go dormant, you can’t suddenly start watering, and then discontinue watering, and then water again. That’s too hard on the grass.

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“You don’t want to half-water and go back and forth between dormant and watering. You’ll stress out the grass,” Maurer says. A dormant lawn will come back to life after a good rainstorm. “The lawn will come back naturally, just like it does when it goes dormant in winter.”