I have been watering my lawn using our sprinkler system, but how do I know how long to run my sprinkler? DT

Sprinkler systems are a wonderful invention for both our lawns and our gardens. But you are correct, how do you know how much water your landscape needs? The unfortunate reality is that most of us tend to overwater. When we do this, we are not only wasting water but wasting money as well.

This time of year, Bermuda lawns need about an inch of water per week and fescue lawns need about 2 inches per week. But how long do you leave your sprinkler system on to accomplish that? This is especially difficult to calculate with different watering zones that use different sprinkler heads in a variety of patterns. The only way to know for sure is to do something we call an irrigation audit.

An irrigation audit sounds like a fancy name, but in reality, it’s just doing a few tests to see how much water your sprinkler system is putting out in a given amount of time. Here’s how you do it.

First off, you’re going to need something to collect the water for your experiment. They make water collection cups specifically for this purpose which are not very expensive, however you can use something like empty tuna cans or cat food cans if you have those available. You’re going to need several of these so just make sure they are alike. Consistent container size will help you get more accurate results.

Now that you have half a dozen or so collection cups, scatter them around in a regular pattern in a single irrigation zone approximately 9 or 10 feet apart, then start your sprinkler in that zone and let it run for 15 minutes. At the end of this period of time, measure the water in each of the cups, add them together, and the divide by however many collection cups you are using. This will give you the average for that particular zone. Now repeat that same process for each of your watering zones.

So, let’s say you ran the test on your first zone and your average was 1/4 of an inch for a 15-minute period of time. If you have a Bermuda lawn, Bermuda lawns need about an inch of water per week so to get your inch of water in this zone, you’ll need to run the sprinkler for an hour during the course of a week.

To make the best use of your water, it’s good to water more deeply and less often. This means that to accomplish your 1 inch of water per week, you should run the sprinkler on this zone for about an hour in a single pass or perhaps twice a week for 30 minutes. Try to resist a little every day because this trains your roots to stay near the surface to meet their water needs when what we want is the roots to reach down, deeper into the soil. With deeper roots, they’ll be better suited to survive.

That’s about it. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Tom Ingram