Turf Design Build Magazine - December, 2012
Laying the Groundwork
Planning is essential before installing an irrigation system
"Irrigation is not as simple as it seems - there is a science to it," says Craig Borland, senior customer resource specialist with Toro. For landscape contractors who design, install or work with irrigation systems, there's plenty to know and understand. There's lots of irrigation technology on the market today, but even in an era of smart clocks, moisture sensors, weather stations, and Internet and satellite controls, "you still need to follow the basic rules of irrigation, those are still critical," says Borland.
Before designing an irrigation system, it's essential to start with some background research. "I can't stress how important it is to take your time and do your homework," says Borland. "What do you have for flow? What do you have for pressure at the point of connection? You have to find out what you have, because if you don't do that, you're really just throwing a dart and hoping for the best."
The next step is to take the property and do some hydrozoning. In a nutshell, hydrozoning is a plan that lets you water plants with different water needs separately. "If you have a turf area, it needs to be irrigated on its own setting. If you have a flower bed, it needs to be irrigated on its own setting," states Borland. "You have to break everything down into hydrozones."
Third, Borland advises placing sprinkler heads starting in the corners and making sure the distances match the head sizes: "If it's a 12-foot nozzle, the heads are 12 feet apart. If it's a rotor, they're roughly 35 feet apart. This lets you make sure you have head-to-head coverage within each hydrozone."
It's in step four of his outline that zoning of the irrigation system itself takes place. "If the maximum flow rate on the property is, say, 12 gallons per minute, then the heads you put on each zone can't have a demand of more than 12 gallons per minute," says Borland. "If you have a large turf area with 60 heads, you need to add up the flow requirement for each nozzle and make sure to map it out so you don't exceed 12 gallons per minute in any way."
Zoning is also the time to be sure that like equipment types are grouped together. "If it's a rotor, you want to put all the quarters on one zone, all the halfs on one zone, and all the fulls on their own separate zone. Separating out the different-shaped circles gives you better matched precipitation," Borland points out. Because rotors move at roughly the same speed, putting quarter and half rotors on the same zone would mean that the quarter units would cover each area twice for each time the half units covered an area once, resulting in some parts of the property getting twice as much water as others. Creating a large number of separate zones is sometimes impractical, though, and compensating by using different nozzles to equalize water delivery is another solution, he adds.
Flower beds and turf do not have the same irrigation requirements, so the irrigation system should be designed so plants receive the amount of water they need in order to thrive.
Photo courtesy of Rain Bird.
Borland says that once the number of heads for each zone has been determined based on need and flow capacity, installers need to consult spec charts to see that the correct piping size is being used. "If you have 12 gallons per minute, you need a pipe that can handle 12 gallons a minute safely," he emphasizes. "If you exceed 5 feet per second velocity, bad things, such as water hammer, can happen." A smaller pipe doesn't produce higher pressure, simply more velocity, explains Borland.
Choosing the right controller is also important to be sure that the established zones all work properly. There is a huge range in the sophistication (and price) of irrigation controllers available. "You need a clock that will handle the number of zones you've laid out and has the flexibility to manage the water demands of different plant types with different run times," says Borland. "If you have a property that's all turfgrass, you don't need all the bells and whistles. If you have a gorgeous landscape that looks like a miniature arboretum, you're going to need a lot of zones, so you'll need a lot of flexibility from your clock."
Borland says that the Irrigation Association (www.irrigation.org) and manufacturers are great sources of information for installers who have questions about the right equipment and techniques to get the job done. "We want our industry to be knowledgeable, because a knowledgeable industry is a better-performing industry," he says.
Before designing an irrigation system, it's essential to start with some background research. "I can't stress how important it is to take your time and do your homework," says Toro's Craig Borland. This involves studying the layout of the property as well as the pressure and flow rate of the water source.
Photo courtesy of Toro.
Jeremy Mansell, senior technical trainer for Rain Bird, says one of the most common mistakes made when installing irrigation systems has to do with mixing different types of equipment on the same valve. "Trying to irrigate a grass area and a shrub hedge together, or trying to use a spray head and rotor on the same valve, doesn't work," he states.
Hydrozoning, he explains, is a process that allows for different areas to be irrigated differently, and similar planting materials to be irrigated similarly. This is what allows rates and run times to be dialed in for each part of the landscape. Most landscapes don't come prepackaged in a way that is best suited for easy irrigation. "I don't know many landscape designers who focus on this first when putting together a plan for a property - they have their own goals," says Mansell. So the responsibility often rests with an irrigation system designer or installer to tailor that system to the landscape.
Hydrozoning is a plan that lets you water plants with different water needs separately. "If you have a turf area, it needs to be irrigated on its own setting. If you have a flower bed, it needs to be irrigated on its own setting," states Craig Borland. "You have to break everything down into hydrozones."
Photo courtesy of Toro.
That's fine for new installations, but what about cases where existing irrigation systems need to be changed to correct mistakes made during the initial installation? "New equipment and technology [are] making that easier," states Mansell. He cites the common mistake of placing pop-up spray valves on the same zone as a sprinkler. "They have very different application rates, and it used to be a huge labor problem to go in and locate pipes underground to dig them up and separate piping into two different valves. Today, depending on the size of the area, there is equipment called stream rotor nozzles that fit on a pop-up spray body, but are more closely tied to rotors. Often they can go on the same valve together."
The number of drip irrigation systems now on the market also makes it easier to irrigate plants with different water requirements, adds Mansell. Where plants within a bed with very different water needs once would have required separate zones, "because there's such a huge range of low-volume emitters available, and all these different flow rates are possible, you can make it work on one valve," he explains.
One common mistake is placing pop-up spray valves on the same zone as a sprinkler. "They have very different application rates," explains Jeremy Mansell, senior technical trainer for Rain Bird.
Photo courtesy of Rain Bird.
Rain Bird and other manufacturers offer training classes and other resources to guide installers through the process of customizing an irrigation system. In those classes, Mansell says he emphasizes that every site is different, and all the variables (plants, soils, exposure, size, etc.) must be considered before the best combination of different zones and irrigation equipment can be determined.
"You have to know what the planting plans are going to be before you set the zones out," agrees Bryan Smith with the Clemson Extension Service in South Carolina. "You can use as many zones as you need; other than the cost of the valving and the piping, it doesn't really matter. Fewer is generally preferable because it lowers those costs, but if you have widely different-water-need plants in the same beds, you may need multiple zones in different beds to accommodate that." When possible, he advises landscapers to craft designs that allow them to get the foliage and texture and color they want, while keeping plants with similar water needs together.
No matter the number of zones required, it's especially important that all of the zones have similar water flow when using well water. "You make the most efficient use of your pump when all of your zones have a similar flow rate," Smith explains. This includes drip irrigation used in beds, which will run for long periods of time. "On city or county water that doesn't make a difference, but it's not a very efficient use of the pump, because the drip might only be putting out 2 gallons per hour," he explains.
He's seen some systems that have the drip irrigation at very low rates, but are set to run every time any other zone is running. Smith also cautions those planning to use well water and drip irrigation to be sure the iron content is low, as the iron will plug up the emitter holes.
Properly setting up each zone sometimes requires extra piping, notes Smith. For example, he sees situations where irrigation contractors will install sprinklers on a lawn area, but then come to a small corner and use a spray head there because the size of its throw fits. "But a spray head applies water twice as quickly, so that area will stay wet and flooded," he explains. "The way to do that is to find a zone that's run on spray heads and run a pipe all the way around to that corner and put that spray head on a spray head zone. It's a little extra work and a little extra money, but that's the right way to do it."
Confirming pressure and flow rate is essential before determining how many zones will be required for a given property, and what type of irrigation equipment will work best for each zone.
Photo courtesy of Rain Bird.
In some cases, a little extra time during the landscape design phase can help create a more effective irrigation system. "Oftentimes people don't put plants into groupings. They'll put one tree here and one tree there; one shrub here and one shrub there," says Sarah Browning, extension educator with the University of Nebraska-Lincoln. "Grouping plants together, especially plants with the same water requirements, can make a big difference." Conversely, putting plants that need a lot of water with plants that only need a little, for example, can increase the challenge of designing an effective irrigation system. "That makes it difficult from an irrigation perspective, and it also makes it difficult to keep the plants alive," she states.
Browning recommends that anyone designing landscapes and/or laying out irrigation systems should look for solid scientific information on the water needs of the plants being used. Data for most trees and shrubs can be found online, while local extension offices can help with ornamentals, she notes. "The site itself, and the soil type - the water-holding capacity and percolation rate of the soil - are also critical," Browning explains. "That lets you know how much water can be applied in a certain amount of time with a certain type of sprinkler head without having water runoff."
If there are different types of soil on the property, that can impact the number of zones needed and the layout of those zones in order to water all areas effectively. If there is clay present, for example, it's good to have a zone that can be run several times a day for shorter durations to get the water deeper without running off. Conversely, if there are well-drained soils and trees present, it helps to have a zone that can utilize longer run times to get water down past the turfgrass and to those tree roots.
"Oftentimes people don't put plants into groupings. They'll put one tree here and one tree there, one shrub here and one shrub there," says Sarah Browning. Hydrozoning a property allows each type of plant, from turf to trees, to get the proper amount of water.
Photo courtesy of Rain Bird.
To arrive at solutions to these issues, Browning recommends that landscapers convert typical irrigation figures (often gallons per minute) into numbers that mean more from a horticultural perspective (inches of water being applied). "Most plant or turf recommendations will be in inches of water," she says. "We often see cases where people have no idea how many inches of water their system puts out in a given period of time, and that's essential information. You need to know the output of the system in order to put on the right amount of water for each plant type."
Patrick White is a freelance writer based in Middlesex, Vt. Over the past 15 years he has covered hundreds of landscape installation and maintenance projects. He is always on the lookout for unusual stories and cutting-edge installations.