How Much Water Do You Really Need?

Plant needs and irrigation performance

Photo Courtesy of Utah State University Extension.

Utah State University extension personnel conduct an irrigation audit.

Most people now know that it’s important to conserve water. For those in the lawn care and landscape business, and their customers, that means irrigating only as much as necessary. While that sounds simple, actually applying the correct amount of water takes some work, and it requires knowing how much water is actually needed and how much an irrigation system is actually applying.

While every area of the country—even specific locations within the same region—may have different irrigation requirements, there are some general rules to follow to help gauge how much is needed and to be sure the system is supplying the correct amount.

One common challenge is to balance the water needs of various parts of a landscape. “With turf species, we have a really good idea about water requirements. A lot of that information is available locally through land grant university systems. There’s just been so much more research done on turf than on ornamental plants. It gets fairly complicated when it comes to ornamental plants,” says Kelly Kopp, associate professor and water conservation/turfgrass extension specialist at Utah State University, who oversees irrigation audits.

In situations where both turf and ornamentals are being watered on the same zone, the amount of water sufficient for turf will typically be more than sufficient for everything else. “That’s not true for annual flowers, they require a lot, but in general, turf­grass is going to be the higher water-using plant in the landscape,” says Kopp. The simplest approach is to water the turf efficiently and assume that the ornamentals will be covered sufficiently with that same amount, she explains. Then, monitor the ornamentals for signs of under or overwatering.

Part of the reason for our greater understand of the water needs of turfgrass versus ornamental plantings has to do with the substantial amount of research that’s been conducted in the golf course maintenance industry, on sports fields, etc., but another reason is the sheer number of different ornamentals, each with its own unique water needs. “There are hundreds of varieties of bluegrass, for example, but the water use between them isn’t going to vary dramatically,” she explains. “On the other hand, with all the different tree species and perennials and shrubs and groundcoverings, there are just so many that you could spend a lifetime working on the water needs of all these different things and never even scratch the surface. It’s just sheer numbers.”

Photo Courtesy of Utah State University Extension.

Supplying thecorrect amount ofwater requiresunderstandingthe needs of theturfgrass/plantsin a landscape,as well as theuniformity andapplication ratesof the irrigationsystem itself.

Whenever possible, Kopp says it’s “most definitely” a good idea to get turfgrass and ornamentals onto different irrigation zones to better give each the amount of water it needs. “That requires a lot of front-end planning with both the plant selection and the irrigation system. For the most part, people are working with a system that they’ve inherited, but there are some modifications that can be made to improve existing systems. Adaptors that can be placed on standard spray heads that will turn them into drip emitters, for example.”

Even though water needs for various turfgrass species are generally known and available from extension offices, irrigating turf efficiently is not always a simple matter. “People never ask, ‘How much water does my turf require?’ They always ask, ‘How long should I run my sprinkler?’” says Kopp. “They often don’t understand that every system is going to be different. Just the difference between rotor head versus spray head is huge. So, I can’t just tell them, ‘Run it for 20 minutes.’

“Some of the challenges in determining the proper irrigation program for a landscape have to with inefficiency in irrigation systems, as well as the fact that many people don’t know how much water their irrigation systems are putting out,” says Kopp. That’s why the intensive irrigation audits she oversees with begin by determining what the application rate of a particular irrigation system is.

“Without knowing that, you can’t know how long to run it to put down, say, 1 inch of water,” points out Kopp. After all, even if you know how much water a landscape needs, unless you know the rate of the irrigation system itself, it will be impossible to ever hit that magic number.

After an audit, most extension agents can provide a schedule that will vary during the growing season and will be based on historic climate data, she says. “There are some states that now have statewide weather networks and can give you real-time data, but most states are still using historic climate data, which is fine,” she says. “It typically uses a 30-year average, so in a wet year it will be overestimating [the plant’s irrigation needs] and in a dry year it will be underestimating, but it’s much more in the ballpark than what most people are currently doing.”

Kopp adds that it’s important for those setting up irrigation programs to keep in mind that turf and other plants typically don’t need as much irrigation during cooler months. “We realize a lot of savings during the fall and spring,” says Kopp. “Most systems are set up for the middle of the summer, and then they never adjust it. We really emphasize changing the schedule throughout the growing season.”

Jacob Johnson, conservation specialist with the city of Austin (www.waterwiseaustin.org), wholeheartedly agrees about factoring in the season when programming an irrigation controller. It’s one of the things that program emphasizes when conducting irrigation audits. “After we offer a recommended schedule, we ask that the operator of the system become actively involved with it,” says Johnson. “Our recommendations are for the summer, but we really encourage people to seasonally schedule, during the spring and fall; when it’s cool at night and the ET rates are down, you can get by with less,” he explains.

Johnson says another common water-wasting mistake is “watering up” to the needs of one specific plant or area. “On a zone, if there’s one plant that has a high water need, they want to run that zone for a long time. Instead, we recommend watering at a rate for the rest of the plants and then hand-watering that one plant that needs more,” he explains. “If you see that one larger area needs more water, that doesn’t mean you want to water the entire yard more,” says Johnson.

After first determining how much water an irrigation system is putting out in gallons per minute by monitoring the water meter during operation of each zone, the auditors in Austin then “walk the system” to look for deficiencies as well as take stock of the landscaping. “We look at plant material, the sun exposure, etc. We also look at the soils. Around here we have a lot of clay soils, so we factor that into the recommendations,” Johnson explains. Those recommendations are also based on water requirements for the turfgrass in question, as well as historic ET rates.

Austin’s irrigation recommendations uses a two-day-per-week irrigation cycle designed to provide effective, deep watering. “That gets the water deep into the rootzone, while giving the ground enough time to dry out so that the roots continue to look for water. If you water every day, the roots know they’re going to get water so they can stay shallow, which can lead to more problems,” he explains.

Johnson emphasizes that even after a professional provides a recommendation for irrigation, it’s important to monitor the plants. “If it’s doing really well on the recommended schedule, you might be able to bring the irrigation down a little more,”

In Utah, where Kopp has been involved with irrigation audits for 10 years, she says that over that time the typical distribution uniformity of the irrigation systems evaluated is about 50 percent. “That means that if you’re trying to apply an adequate amount of water, you’d have to run it for twice as long. With that low of efficiency, we really shouldn’t even give people a program, but this is a public program, so we talk a lot with them about how to improve the efficiency and then give them a program,” she says.

About 10 to 15 percent of the audits conducted by the Utah State University extension personnel are on commercial or institutional landscapes with professional grounds managers. “That’s really fun, because we can talk about a lot of different issues in depth, they’re excited and motivated, and we know that they’re going to use the information,” she says.

Kopp has also given workshops to professional landscapers to help them do audits themselves. Part of the point of the workshops was to give these professionals the tools needed to do routine evaluations of irrigation systems, something that’s important especially in cold climates. “Every year there’s freezing and thawing, heads are tilted and popping out of the ground and breaking. You really have to keep up with it, so that the system is continually operating as efficiently as possible. If we could get them to turn the irrigation system on and check it out once a year, I would be thrilled. A lot of times irrigation systems are run at night and people never even see them.”

Kopp says part of the challenge is making people aware that overwatering turfgrass can harm plant health. “I sometimes wish that turf would start showing the detrimental effects earlier rather than later, but it can take quite a lot of overwatering before it starts having disease and nutrient issues show up,” she says. “Some ornamental plants show the effects of overwatering pretty quickly. From a visual standpoint, turf doesn’t help us very much, so that’s where education comes in.”

Patrick White is a freelance writer and editor who is always on the lookout for interesting and unusual stories.