Watering your grass is simple if you keep two goals in mind.
- First, you want to water long enough to moisten the root zone without wasting water. The root zone is simply the soil surrounding the roots.
- Second, you want to let the soil dry out somewhat between watering so that the roots can take up oxygen.
It’s not a good idea to water your grass every day. Watering every day doesn’t allow enough air to get into the soil, which leads to shallow, unhealthy roots.
How long to water?
Let’s start with the first step. Whether you use a hose-end sprinkler or an automatic sprinkler system, you have to figure out how long to run it.
This is something that you have to figure out for yourself for both your front yard and back yard. Sprinkler systems are so different that it could take anywhere from 10 minutes to 60 minutes or more.
Even different zones in the same yard might require different run times if the sprinkler type or spacing is different. That’s why it’s important to actually test how much water your sprinklers apply over time.
The power of the test
Landscape experts have determined that if you apply ½ to 1 inch of water each time you water, that will moisten the soil to a depth of 6 to 8 inches. That’s generally how deep the roots of your grass should be.
Water less and you’ll have shallow roots. Shallow roots lead to thin, stunted grass. Water too much and the moisture will move through the root zone into the subsoil where the roots can’t reach it. That wastes water.
The best way to test your system is to measure how long it takes for each zone of your sprinkler to put down ¾ of an inch.
Here’s how you do it: Get at least 6 empty soup cans or cups (all the same size and shape) and space them out one zone of your sprinkler system. Run the sprinklers in that zone until there is, on average, a depth of ¾ of water in the cups. If you overshoot it, don’t worry, just empty the cups and try again.
Once you determine the “run time” for that zone, write it down. Repeat these steps for all of the sprinkler zones of your system.
The cool thing is, once you know it takes say 20 minutes to collect a depth of ¾ inch in zone 1, you now have a customized starting point for your sprinkler schedule. Each time you water, you want to run zone 1 for about 20 minutes. You may have to tweak the time up or down once you see how the lawn responds.
Runoff causing problems?
When you do this test, you may find one of two common problems.
One problem is that water starts running off the landscape onto the sidewalk and into the gutter before you get ¾ of an inch in your cups. We call this problem runoff. It’s caused by soils that have very small spaces and therefore cannot absorb water very quickly.
Here’s how you water without causing runoff. First, start watering and see how long it takes to get runoff. Stop watering and write the length of watering time down. Wait an hour, then start watering again. If you get runoff again before you get ¾ of an inch in your cups, stop watering and write the second length of watering time down.
Repeat these steps until you get an average of ¾ of an inch in your cups. These measurements help you get an idea of the average number of minutes you can run your system before you get runoff.
Your notes may look like this:
Zone 3:
- Run time 1 = 9 minutes (then runoff)
- Run time 2 = 7 minutes (then runoff)
- Run time 3 = 6 minutes (then reached 3/4 inch depth in cup)
Once you’ve figured this out, you know you will have to schedule your system to “cycle and soak.” To cycle and soak means to run the zone for the number of minutes before you got runoff, wait for a period (usually an hour), then water again, and stop if needed, etc. You simply do this until you’ve applied ¾ of an inch total. Once again, this is a starting point. You can tweak your schedule if you need to do so.
For zone 3 in the example above, we could schedule its program to run, say, 3 days per week on Monday, to have a run time of 7 minutes each time it watered.
To cycle and soak, we would then add three start times each 1 hour apart. It the start times could be 3 am, 4 am and 5 am depending on how many zones were on the same program. The total run time would still be about 21 minutes, but rather than half of the water running down the gutter, it would be soaking into the soil where the grass can use it.
Wild results?
The second problem you may run into is that when you run your system, you get very different amounts of water in your cups. For example, one cup may have an inch of water and the second cup may be dry. This result means your system is not applying water evenly because something isn’t working right or the system was not designed well. You might need to dig into this problem deeper or call a professional to help.
To review, you’ve just figured out how long to run each zone in your system each time you water. Keep this information close to your sprinkler timer or in a place you can find it.
How often to water?
Next, you need to figure out how often to run your system. It’s tempting to set your sprinkler system for three days per week and walk away. You can do it that way, but you might be wasting a lot of water. There are two other options.
Adjusting by the season
One option is to set your system to run either one or two days per week during April and May. If you see your grass turning dull grey green or there are visible footprints in the grass 30 minutes after you walk on it, you need to water again.
You may have to add another watering day to your schedule if the weather is warm or your grass needs to be watered more often.
Then, when June rolls around, change your system to run either two days per week or three days per week if you are seeing the signs that the grass needs water more often.
When September comes, once again set your system to run one or two days per week. By changing the schedule 2-3 times per year you can save a lot of water. Letting the grass show slight signs it needs water won’t harm it in any way. Grass is actually very resilient.
The on-demand method
The other option is to use what I call the “on-demand” method. I learned this from Dr. Tony Koski, who is the turfgrass specialist at Colorado State University.
Simply leave your timer in the “off” position and let the grass tell you when it needs water. Water when the grass needs it by starting the programs manually on your sprinkler timer, and don’t water when it doesn’t need it.
This is the method I personally use. It’s a good one if you are around most of the time in the summer and like to pay attention to your grass. You can save the most water with this method and still have a beautiful lawn.
Here’s how I do it at my house. In my sprinkler system, I know I need to run each zone of my sprinklers for about 75 minutes (since I have MP rotator nozzles) each time I water. I look at the grass each day in the afternoon and look for the dull gray green color or visible footprints 30 minutes after walking on it.
If I see those signs, I water. Then I turn my system back to off. I don’t water again until I see the signs.
The trick with this method is that once you see the signs, you can’t wait a few days to water. You have to water as soon as you see the initial signs of drought stress.
If you wait too long, your lawn will start to turn brown because it’s beginning to go dormant. Too much drought repeated stress and your lawn will get thin over time.
Like I said, this method works well if you are in town and paying attention. When I go out of town, I set my system to run 2-3 times per week until I get back. Then I go back to this on-demand method. When the weather is cool or rainy, I might only water once every 1-2 weeks. When it’s hot, I water much more frequently.
Summary
Do a cup test to see how long to run each zone of your sprinkler system. This tells you how long to water each zone.
Add the cycle and soak strategy to your schedule if you have a runoff problem.
Address any coverage issues by repairing your system or modifying the spacing of your sprinkler heads.
Change your schedule 2-3 times per year so that you’re watering 1-2 times per week in cool seasons and 2-3 times per week in hot weather. Alternatively, use the “on-demand” method to water only when the grass shows signs it needs water.
By getting a good sense of how long and how often to water, you’ve gone a long way towards growing a beautiful lawn that you can afford. It also means you are acting as a steward one of the most precious and limited resources in Colorado: water.