2019-08-18 sc-mastergardp1

A simple irrigation audit will determine how long to run sprinklers during the summer. Tom Ingram/for the Tulsa World

It’s been so hot outside. How do I know how much I should be watering my lawn? JB

Keeping our growing things alive in July and August can be a challenge in Oklahoma. However, there are some general guidelines that can help.

If your lawn is primarily Bermuda (or another warm-season grass), it needs about 1 inch of water per week this time of year, while fescue (or other cool-season grasses) need about double that or 2 inches of water per week.

Whenever we tell someone this, the next question is typically something like, “Then how long do I run my sprinkler to get an inch of water?” The answer to that question necessitates you doing what we call a “simple irrigation audit.”

For a simple irrigation audit, you are going to need nine collection cups, a pen, paper and a calculator (most of us will probably need a calculator). Collection cups can typically be purchased from an irrigation supply store or you can use clean metal cans that might previously have contained tuna, cat food or perhaps tomato paste. You will get the best results if all your collection cups are the same.

If you choose cans, you can use a ruler and a fine-tip permanent marker to mark the outside of the cans in ¼-inch increments. Or you can just measure the collected water by sticking a ruler directly into each collection can.

To collect your measurements, place your nine collection cans about 8 feet apart in something close to a 16-by-16-foot grid. For best results, do this in one sprinkler zone at a time.

Next, let your sprinkler run over your collection grid for 20 minutes. After the collection period is over, measure the amount of water in each of your collection cups, add up the total amount collected (now it’s calculator time), and divide the total by nine because you were using nine collection cans. This will give you an average amount of water your collection grid area received in 20 minutes.

So let’s assume your average measured amount was ½ inch. This means for every 20 minutes your sprinkler system runs, your turf will be receiving a ½ inch of water. If you have Bermuda grass, which needs 1 inch of water per week, you are going to need to water twice that amount, or 40 minutes per week. You can split this up into two watering sessions per week of 20 minutes each.

If you have a fescue lawn, which needs 2 inches of water per week, the math says you would need 80 minutes per week, which can be split up into two watering sessions of 40 minutes each. This would not be a total for your yard, just for that zone. As you can imagine, each zone is going to be a little different, so for complete accuracy, you would need to repeat the process for each zone.

Performing this simple irrigation audit will likely end up saving you money, as most of us overestimate the water needs of our turf and end up “pouring money down the drain.”


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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.