Deep Watering Grass: The Science of Watering Mature Turf

September 30, 2020


Deep Watering Grass: The Science of Watering Mature Turf

There is only one substance that all known life forms cannot live without: water. Hot or cold, fresh or salty, plentiful or hardly any—all life needs water. And your turf is no different. Without water, your grass would shrivel up and die after just a few weeks. What allows more drought-tolerant varieties like TifTuf™ Bermudagrass to go for weeks without rain or irrigation is their ability to draw water from deep underground, where there is still some moisture. Typically, plants with deeper roots can better withstand periods of drought. Also, plants with shallow roots are more susceptible to damage from stressors like drought, foot traffic, and disease. So it’s no surprise that lush, green grass requires deep roots. Mature turf should have deep roots, and to get deep roots you need deep watering.

How Often Should You Water Mature Turf?

Most landscapers will throw out a standard answer. You should water your grass with one to two inches of water once a week. This is convenient for homeowners because it means you can pick one day a week—typically a weekend—and water your lawn on the same day every week. While this may be easier for homeowners, it is not the best way to water mature turf. It’s certainly better than watering daily, but it doesn’t account for differences in weather, soil conditions, and plant varieties. The best way to determine when to water your grass is not to follow a set schedule. Rather, you need to pay attention to the grass itself.

The Science of Deep Watering

The key to watering mature turf is to let the grass reach the early stages of drought stress before you water. This may seem anathema to the home lawn enthusiast, who would never want to intentionally stress their turf. But the science indicates that this kind of stress is actually necessary for a plant to grow the deep roots that will allow it to withstand actual drought.

When a plant—in this case, grass—experiences mild stress from water deprivation, it releases a hormone called Abscisic Acid (ABA). As the drought persists and more ABA is produced, the grass takes action to preserve its water. The stomata, tiny pores in the grass blade, close up to preserve water, and the cuticle, the surface of the grass blade, grows thicker. The increased ABA causes a plant to grow deeper roots to reach out for more moisture deeper underground.

The goal of deep, infrequent watering is to allow the grass to experience mild to moderate drought stress so that it produces ABA and deeper roots between waterings.

Deep Watering Grass - The Science of Watering Mature Turf [infographic]

When and How to Water

If the goal is to hit a mild drought stage, how often should you water? The answer is that it depends on many factors, including soil conditions, weather, and the variety and health of the turf. The best way to tell when to water is to look for signs of drought stress. One significant sign of drought stress is that the grass blades lose their springiness and will not immediately spring back after you walk on them. If you walk across your grass and see footsteps behind you, don’t fret. Your grass isn’t dying; it has reached the perfect stage of drought stress. Another sign is a change in the color of the grass as the grass blades are bent over. Once the grass has reached this stage, it’s time to initiate a deep watering.

Deep watering doesn’t just mean turning on your sprinkler and leaving it. The goal is to moisten the soil to the full depth of the roots, at least 6 inches, if not more. However, a single soaking may not do it. In perfect, loamy soil, the soil may be able to absorb the water all at once. But depending on the water pressure of your sprinklers and how clayey the soil is, one long watering can often lead to runoff and wasted water.

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Intermittent Watering

Start by turning on the sprinklers for 15 minutes, then come check to see if you are noticing runoff. If water is running off, that means the soil needs time to absorb the water. Turn off the water for 40 minutes or even an hour to let the water soak in, then water for another 15 minutes or until you see runoff. This may seem complicated at first, but if you take notes on your process, you should learn the unique characteristics of your lawn, your soil, and your turf.

Once you know your soil and turf conditions, you can water in spurts just long enough to soak the soil. Keep watering on and off like this until the soil is moist at least 6 inches deep. To test the moisture depth, you can do a simple screwdriver test. Take a long screwdriver and poke it into the soil. The screwdriver will penetrate moist soil easily, but stop when it hits dry soil. If you can easily insert the screwdriver 6 inches into the soil, you are done watering. If not, keep watering on and off to moisten the soil adequately.

Exceptions to the Rule: When You Should Avoid Deep Watering

While deep watering is ideal for most mature turf, there are times when it is not recommended. The most common situation in which you should avoid deep watering is in sandy soil. While loamy or even clayey soil can hold a lot of water, sandy soil cannot. It drains quickly. The soil cannot hold onto water, so infrequent deep watering will just starve the plant of water. You need to water lightly multiple times a week in sandy soil to ensure that your turf has access to enough water.

Also, deep, infrequent watering is only suitable for mature turf. Young turf, newly-laid sod, or freshly-seeded grass needs the top layers of the soil to stay moist at all times. Its roots are not long enough to reach moisture deeper down, and it is not mature enough to handle drought-induced stress. With younger turf, water daily to ensure the top layer of soil is continually moist.

Deep Watering and Sprinkler Types

The type of sprinkler you use to irrigate your turf will have a significant effect on how you achieve deep irrigation. While there are many types of sprinklers, most sprinklers can be described as low-pressure oscillating sprinklers or high-pressure impact sprinklers.

Low-pressure oscillating sprinklers are typically hooked up to a garden hose and spray water in a broad arc, oscillating back and forth to cover a larger area. For anything other than a small lawn, you will have to move an oscillating sprinkler around your yard to cover the entire area. Oscillating sprinklers tend to be less water-efficient since the droplets are sprayed up into the air, where they are susceptible to wind and evaporation. But they provide a slower stream of water, which may allow you to soak the soil without pausing to let the water soak in.

Impact sprinklers use high-pressure to send a stream of water a long distance across your lawn. Different types can rotate or otherwise move to reach your entire yard. They spray a high-pressure blast low to the ground, so less water is lost to wind and evaporation. They are ideal for large lawns since they can spread water anywhere from 15 feet up to 60 feet in a single blast. However, since they spray a lot of water all at once, you need to monitor your lawn for runoff and pause as necessary to allow the water to soak into the soil.

Avoid Timers

Avoid running your sprinkler on a timer. Although it may seem convenient, a timer setup doesn’t take into account the state of your turf and when it actually needs watering. If you like the idea of a timer, one option is to install a smart irrigation system. Some simple systems just use a rain gauge to avoid watering when it has just rained. Other, more advanced systems monitor soil conditions and account for weather information, usually obtained via a WiFi connection.

However you choose to run your sprinklers, it is critical to ensure that the soil, at least the top layers, has time to dry between waterings, so the roots are forced to grow long and deep.

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