Get smart about irrigation with controller tips

During his long career as an irrigation specialist, Don Franklin has seen the evolution of “smart” controllers. They’re definitely a major improvement over standard sprinkler control boxes, those fixtures with the little dials and manual adjustments. But they can have the same issue: Controllers depend on user input.

“You need to do some homework before you set them up,” he observes. “The more you understand, the better equipped you are to program your controller. They need information.”

Smart controllers can make a huge difference in total water use while contributing to a healthier landscape. According to the Regional Water Authority, a Water Sense-labeled controller can save an average home about 13,500 gallons a year.

“But ‘set it and forget it’ is a myth,” Franklin notes. Get to know your landscape a little before you set up your controller, so it can be truly smart.

What your controller needs

Start by understanding how your controller works. Some information is pretty basic, Franklin explains. “Any controller – old style or the latest technology today – needs three pieces of information: Station run times (how many minutes per zone); water days to irrigate; and what time to start.”

A controller becomes “smart” by adding either weather information or soil moisture information, he says. “Then, it automatically makes adjustments to the water schedule.”

Most weather-based smart controllers use evapotranspiration (ETO) in their calculations, Franklin explains. “The sensors factor in wind, humidity, temperature and solar radiation, the heaviest variable in the equation (due to) the lack of clouds. They use an algorithm to determine how many inches of water left the environment in the last 24 hours through evaporation and transpiration, the loss of water from plants.”

These systems then look at past ETO data as inches per day, he continues. “It could be anywhere for .01 inch to a half inch. The smart controller then puts back that amount of water the landscape lost over that last 24 hours.”

Those amounts also are based on another assumption: It’s irrigating tall fescue grass, among the thirstiest landscaping.

“To set the proper run times, you need to know plants, soil and your irrigation system – how much water does it deliver per hour,” Franklin says. “Most controllers ask you to program run times for worst-case scenarios – the hottest days in July or August. Then, the smart controller cuts back from there.”

But what if you’re irrigating shrubs, trees or other plants? The controller needs that information, too.

“You need to look at the plants – what are you growing?” he adds. “And get your fingers dirty. Look at the soil.”

Check your soil

Franklin suggests using a soil probe or moisture meter to check how far water is penetrating.

“Check your soil daily. That will tell you how frequently you need to irrigate. Moisture level is like the gas tank in a car. Typically, you let it get half empty before filling up; the same with soil moisture. It’s really the smart way to program your smart controller, with actual observations.”

As for run time, start with your best guess, Franklin says. “First, set run time for what you think it might need. Then, two hours later, look at the soil and see how deep it penetrated. The root zone for most plants is 12 inches. If water is penetrating more than 12 inches, it’s of no value to the plants and you need to back off the run time.”

Also, observe any surface runoff and make adjustments accordingly.

“Some smart controllers are now looking at weather information and predicting usage – which is much, much smarter,” Franklin adds. “They’re able to predict temperature and rainfall three days out, pulling information off the internet. It takes it to another step.

“If there’s a 60 to 80 percent chance of rain, depending on how you set up your controller, it won’t irrigate,” he adds. “It will take advantage of all that free water.”

Now, that’s smart.

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