Campbell Vaughn: Lawn irrigation can be tricky to get right. See these tips to help.

Anyone notice that it is a little warm outside? And when I say warm, I mean how are birds not falling out of the sky because of this heat.

We have had zero days where the maximum temperature was below 90 degrees since June 12. We have also had no rain since June 5 except for a rare, scattered shower.  The 10-day forecast looks horrible. So, the calls that I have been getting are common: “With this kind of heat and drought, how much do I need to irrigate? Is 30 minutes OK?”

My standard answer? “Let’s take a step back and go through this process together.” In other words, I am going to give you the long version of the answer because my job is to educate, not guess.

There are so many variables to consider before deciding how long to run your irrigation system. Irrigation is math with a little science to mix into the fold.

Let’s first talk about the math portion of irrigation systems. There are all kinds of irrigation heads that emit water in all kinds of directions and at different rates. For this column, we are going to talk about rotor head irrigation. These are the standard irrigation heads that are most likely seen in your lawn. You click the “RUN” button on the controller and these things pop us from the ground and start shooting a long arching stream of water about 30 ft. These rotor heads start to slowly move one direction and then at a set spot, they turn the other direction.

Rotor heads come standard with a 3 gallon per minute water flow. Here is where it gets tricky. We assume you are getting 3 gallons per minute, but these heads will take GPM rate nozzles of 1 GPM up to 8 GPM. One head could potentially be putting out eight times as much water than another. Remember that the head rotates, so sometimes they go 90 degrees, 180 degrees or even spin a whole 360 degrees. In the same amount of time, the rotor head watering at 90 degrees is applying four times as much water to that area as the area applying a full circle. Really good irrigation design helps prevent some of these type discrepancies in volume of application, but it isn’t fool proof.

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The science part of irrigation considers how much shade/sun do you get? Sunnier areas are hotter and evaporate water faster, so they usually need more water. Sandy soils don’t hold moisture for as long as clay soils do, but clay soils need slow application of water to infiltrate. Compacted soils don’t take water as well as loose soils. Zoysia grass needs more water than Tif Tuf Bermuda. A 3-year-old pecan tree will drink 10 gallons of water a day in August, but a 25-year-old pecan will drink 300 gallons of water a day. Hydrangeas need more moisture than camellias. Watering in the morning keeps evaporation at a minimum so water can get to where it needs to be, in the ground. I can probably come up with 400 other factors to consider in deciding how much you need to irrigate.

In saying all this, I really can’t tell you for how long you should run your irrigation system, but I have a foolproof trick that will help you figure that number out; a plastic dish. Get an old beat-up plastic dish that used to be a home to deli ham and put it right in the middle part of your lawn that looks like it needs the most water. Turn your irrigation on and see how much water you get in that container in your normal watering cycle. If it isn’t three-quarters inch of water, then increase your time. If it is over three-quarters inch of water, decrease your time. This time of year, if you water twice a week to equal 1.5 inches of water total that should be good. If it rains three-quarters of an inch one evening, then turn the controller back to one day that week.

Don’t be afraid to use a shovel to see how much moisture there is in the soil from the surface to 6 inches deep. At 101 degrees, it would be fine to irrigate one more time a day if you need to replenish moisture levels.

You also may want to take a lawn chair and sit by that plastic dish and watch it fill up to stay cool.

This article originally appeared on Augusta Chronicle: Campbell Vaughn: Lawn irrigation hack to see how much water is needed