You’ve seen it before: lush, green grass tainted by dry, brown circles—almost like crop circles or donuts.
The culprit
Most likely they're not an issue in the winter months, but as soon as the summer arrives, you may start to notice these dry, brown circles (donuts), resulting from evapotranspiration (ET) and is an indication your irrigation system has spacing problems (also known as stretched systems).
Jeffrey Knight, Ewing’s Director of Learning and Development, said the number one problem with spacing is that it’s almost always stretched.
“This is a problem because the uniformity isn’t consistent throughout the entire radius of the heads' spray,” said Knight.
Once you correct the spacing problems, the brown, dry circles will go away. If you still have brown circles spoiling your turf, then you’re dealing with a different issue entirely—most likely a fungus.
Lay off the donuts! Abide by the 10% rule
Head-to-head coverage is what most contractors try to achieve on a new install. Unfortunately, the majority of irrigation systems don’t have overlap.
“In order to eliminate donuts plaguing your turf and to achieve higher uniformity, you’ve got to have equal distribution of water with head-to-head spacing,” said Kirk Burris, Branch Manager of Ewing’s North Richland Hills, Texas, store. “When spacing your sprinkler heads, it’s important to make sure there’s a 10 percent overlap of spray from one head to another.”
To be most efficient with your watering practices, it’s important to keep consistency with your sprinkler heads and nozzles. They shouldn't be mixed on the same zone.
“You don’t want to use MP Rotators with HE-VAN nozzles,” said Burris. “They each have different watering requirements.”
It’s equally important not to add heads at random. Burris said if you add heads sporadically, you’ll have to worry about whether your gallons per minute (GPM) will work correctly or not.
Another important element of smart irrigation (efficient watering practices) is understanding your precipitation rates. You don’t want to oversaturate your turf, as it’s an irresponsible practice of watering. Over watering can often lead to fungus problems, while under watering can lead to dry, dead, brown spots in your turf.
Knight explained that by examining the profile of a sprinkler head’s spray pattern, you can determine the precipitation rate is typically greater at or near the head. However, the precipitation rate is less at the farthest point of that head’s radius of throw.
Too much, too little: A common issue of stretched systems
Just because all your grass is getting wet doesn’t mean there’s an equal distribution of water. Making sure your sprinkler heads overlap each other ensures equal amounts of water on the entire area of your lawn so you’re not left with over watering in some areas, while barely watering in other parts of your lawn. Having proper pounds per square inch (PSI) will negate this problem.
“If your system has too much PSI, you’ll have problems with misting, and you’ll have loss of water and be wasteful,” said Burris. “But if you don’t have enough PSI, you won’t have the pressure needed to throw water from one head to the other.”
Spacing recommendations
It’s important to note spacing recommendations in manufacturers’ catalogs are based on laboratory conditions—perfect environments, free from outside conditions, such as wind, ET and other weather elements. When outside in the elements, a good rule of thumb is if the distance from one head to another is 12 feet, choose a nozzle that will reach 15 feet. Overlapped distribution of water (10%) is better than the alternative.
If enough GPM and PSI are available, you can add your desired heads. But if your system is lacking the proper amounts of GPM and PSI, then you’ll have to adapt to the following solutions, provided by Brian Dixon, Branch Manager of Ewing's Redding, Calif., store.
"You can replace popup heads that have fan sprays with low precipitation rate rotary nozzles, such as Hunter MP Rotator, Rain Bird R-VAN and Toro Precision Series Rotating Nozzles," Dixon said.
Rotary nozzles allow you to step down with regards to GPM and PSI. In addition, you’ll conserve water and be more water efficient.
The big picture: Benefits of a properly spaced system
There are many benefits of having a properly spaced irrigation system. Proper spacing ensures even distribution of water and prevents dry spots. Your irrigation system will be more efficient and your landscape more beautiful.
Comment below about your experiences with donuts in your turf. For more information and help with proper head-to-head spacing on your next project, visit your local Ewing store.
Still have irrigation issues? Check out this blog for other possible solutions.