The key to irrigating your lawn is to remember the term Deeply and Infrequently. This segment shows an easy way to figure out how frequently to water by using an evapotranspiration table for your area supplied by the K-State Weather Data Library.

Produced by the Department of Communications at Kansas State University. For more information, visit our website at:

How Often to Water Lawns

One of the key questions when we’re trying to figure out how to irrigate our landscape is “how often should we apply the water?” The key term that we use when we’re applying water to turf, trees, flowers, or vegetables is always going to be irrigate deeply and infrequently. That means to water a whole lot of water today and then wait as many days as possible before we irrigate again.

A lot of people when they think about plants and the plant roots, they think that the function of the roots is solely to absorb moisture out of the soil to provide water for plant growth. The problem is that plant roots need air to breathe. So, if we’re irrigating every day, or if it’s raining every day, the soil will be saturated, and there won’t be any air for the plant roots to grow and be healthy.

Therefore, we want to irrigate deeply to get the water deep into the soil, and then you’ll want to wait as many days as possible so the soil can dry out and new fresh air can move deeper into the soil so that the roots can have good oxygen to breathe under the ground.

The term to remember is deeply and infrequently. But the question is “How deep and how infrequently?” If you’re looking at frequency, you’ll need to use weather data. And the term to look at is evapotranspiration or ET. Go to the K-State Weather Data Library at or other weather data sources, and look at the evapotranspiration for turfgrass, and it will give us an indication of how often to water the lawn. Normally, a general rule of thumb for irrigating a lawn is the use an inch of water per week. So, by looking at the evapotranspiration table and determining when you’ve lost about an inch of water, then it’s time to irrigate.

If you look a the weather data here, you can see for example that on the first of June we lost about ¼ of an inch. On the second of June, we lost roughly another quarter of an inch, and on the third of June, we lost another quarter of an inch. So, that’s about ¾ of an inch. You may want to think about irrigating your lawn on the evening of the third. Or, you could wait until the fourth of June. After the 4th, you’ve definitely lost of full inch of water, and you should then water your lawn.

The important thing to look at on the weather data is that on the eighth of June, there is 8/10ths of an inch of rain. So, when you add up the ET, and you subtract the amount of rainfall, you may not need to irrigate at that time. So, you need to look at the ET and you need to look at the precipitation that fell, and use those two numbers in conjunction to determine when to irrigate.

The term for turf and landscape irrigation is Deeply and Infrequently, and you can determine the frequency by using weather data and evapotranspiration data to determine how frequently you should irrigate your lawn.

This feature story prepared with Rodney St.John, former Kansas State University Research and Extension Turfgrass Specialist. For more information, visit your local county extension office or visit our website at

Horticulture Newsletter

KSU Horticulture Newsletter

Get more information from our weekly newsletter.

Find Your Local Office

Have questions or need help?

Local Extension Office Map

Click the map to find your Local Extension Office.

YouTube Videos

YouTube Videos

Watch K-State Research and Extension Videos.

Kansas Healthy Yards Tagline