Weather Or Not: Irrigation Rain Sensors

Saving water and money, rain sensors make perfect sense for most irrigation systems.

Economical, efficient and easy to install, rain sensors are, indisputably, a good idea. Having been on the market in some form or another for about half a century, these straightforward devices are based on a simple objective: operating an irrigation system only when necessary. Jerry Gunter, general manager, TechScape, Richardson, Texas, summed up the logic underlying rain sensors nicely: “No sense watering your lawn when the Lord’s doing it for you.”

Whether they simulate the rate of moisture evaporation in soil with an absorbent wafer or disk or collect rainwater in a cup, rain sensors know when it’s raining and shut down a system accordingly. While they’ve been around for years, these devices started seeing increased use in the mid-1980s, according to Rick Malkin, product manager, Rain Bird, Glendora, Calif. “They started to come into their own about 15 years ago,” he observed. “Technology got to the point where they were inexpensive and easy to install.”

Conserving water and reducing operating costs, these devices are a beneficial addition to most any system, according to irrigation experts.


    Wind and freeze sensors can be beneficial additions to irrigation systems – but on a more limited basis than rain sensors. Freeze sensors are well suited to climates that don’t experience drastic changes of season and might have unpredictable freezes, according to Kevin Gordon, senior product development manager, Hunter Industries, San Marcos, Calif. These devices are most popular in markets that don’t shut down systems for the winter, he said. “In Dallas, for example, it can freeze one day and the next day be 75 degrees.”

    Similarly, in a climate like Colorado’s, irrigation often takes place in colder weather, Rick Malkin, product manager, Rain Bird, Glendora, Calif., pointed out. “Many times in the late spring or early fall, temperatures will drop, but they’ll still need to irrigate,” he said. Contractors in climates without a definitive seasonal transition find freeze sensors a good way to prevent irrigation rather than shutting off the system completely.

    Freeze sensors are commonly used as safety devices, activated at a pre-set temperature. “These can eliminate any runoff that can cause dangerous icing on a road or sidewalk,” Gordon said. In some areas, freeze sensors are even required by law as a safety precaution. Jerry Gunter, director of irrigation, TechScape, Richardson, Texas, recalled a big automobile wreck that happened years ago in nearby Dallas that was caused by a sprinkler operating in freezing weather.

    In this case, freeze sensors would have provided considerable liability protection.

    Because of this accident, they have since been mandated by law in Dallas, Gunter said.

    Wind sensors, on the other hand, are useful in areas with sporadic wind or if a system is watering a landscape near a glass building, for example, Gordon said. He sees a lot of these devices used in fountains where a big column of water can blow outward onto passers-by. Malkin noted that wind sensors are often used in more sophisticated systems, such as one where effluent water is used under strict regulations and can only flow at a limited velocity.

    – Cynthia Greenleaf

SAVING RESOURCES. Rain sensors conserve water, which is of vital importance, especially in areas where municipal water supplies are increasingly strained because of population growth and population expansion. Rain sensors have saved hundreds of thousands of gallons of water, according to Dave Klever, president, Ecologic, Richmond, Va., which makes the RainBrain rain sensor.

By conserving water, rain sensors also provide a sizeable economic benefit in many cases. After all, “no one gets free water,” pointed out Kevin Gordon, senior product development manager, Hunter Industries, San Marcos, Calif. These sensors can also save on electricity costs if a system relies on a pump for water delivery.

Rain sensors are also a way of maintaining a property’s health, observed Dan Standley, owner, Dan’s Landscaping and Lawn Care, Terrytown, La. “If a property is overwatered, it runs the risk of fungal or insect problems,” he said. With a rain sensor, however, “you’re protecting your landscape investment.”

With many commercial accounts, politics also come into play. “Taxpayers do not like to see sprinklers working when it is raining,” said Dirk Lenie, marketing manager, irrigation division, The Toro Company, Riverside, Calif.

While rain sensors are generally a good idea, they’re not usually necessary in extremely arid environments that receive relatively small amounts of precipitation. In this case, a sensor would have little or no value, Gordon said.

Klever agreed, noting that locations with annual rainfall in the single digits shouldn’t bother installing a rain sensor. “It just wouldn’t be cost effective,” he said.

In some areas, rain sensors are mandated by law, including Florida, which is the only state with an overall rain sensor statute. Laws such as these, which are also locally enacted in areas of California, Minnesota, New York, New Jersey, North Carolina and South Carolina, are generally driven by water conservation concerns, Gordon observed.

EASY TO INSTALL. Rain sensors are simple to incorporate into a new or an existing irrigation system, according to industry experts. Better yet, most sensors are compatible with almost any irrigation components. Usually, setting a sensor up is just a matter of running some wires and mounting a system, Malkin said.

If a sensor doesn’t have a bypass switch built in, contractor Robert Sigsworth always installs one for convenience sake. This makes routine maintenance and other tasks, such as washing fertilizer into a lawn, simpler, said Sigsworth, owner, Robert’s Landscaping and Maintenance, Metairie, La. “If the device is mounted really high on a two-story home and you’re not sure if the cup is full of water, you can bypass it and make the system come on,” he said.

Simple in design, most rain sensors require little, if any, maintenance. With a cup- type sensor, Malkin suggested checking the device occasionally to make sure it’s not full of leaves or dirt, he said.

Matt Piper, product manager, Weather-matic, Dallas, Texas, advised testing a sensor at installation and verifying that it works.

Similarly, Gordon said a periodic visual inspection would be fine. Generally, though, “there’s very little that can go wrong with a rain sensor,” he said.

Basic, no-frills rain sensors are relatively inexpensive, with most retailing between $30 to $40. Many contractors look at these devices as a minor investment that pays for itself in time. And better yet, they’re durable and long-lasting. Gunter has been installing sensors for about 15 years and said he can’t remember ever replacing one.

INTELLIGENT INSTALLATION. Despite their simplicity, even the most effective rain sensor is useless if installed incorrectly. For a sensor to provide an accurate reading, it must be properly located. This means not putting a sensor behind a sign, beneath a gutter or under an eave. If this is the case, “you’re not getting a true feel for actual rainfall,” Standley said.

Malkin agreed, noting that the biggest installation mistake contractors make is not considering the nature of rainfall in relation to the rain sensor. He recalled a few jobs where the sensor was mounted so inaccessibly that he had to crawl up on a roof to deactivate it.

Along the same lines, Sigsworth observed that many of his jobs come from contractors who install rain sensors improperly. “Nobody understands the principle of the rain sensor device,” he said, pointing out that many contractors run the sensor directly from the system timer, which is an easy installation but won’t yield an accurate rainfall reading. For greatest accuracy, always put the sensor in the highest point in the yard and in the most open area, he advised.

Another common mistake is mounting a sensor too close to a sprinkler head. “So when the head comes up, it sprays and fills the cup up and the system turns off,” Sigsworth said. “Meanwhile, it’s a hot, dry day and the flowers are dying.” Other installation gaffes include putting a sensor too close to a bird feeder or underneath a tree. “You don’t want to put it where a tree branch is sitting 3 feet above it,” Sigsworth warned.

And, while this might be obvious advice, avoid putting a sensor on the ground where it can be run over by a lawnmower, said Dave Cujas, irrigation manager, TruGreen LandCare, Naples, Fla. Placing the sensor two stories or higher is generally a good rule of thumb, he concluded.

Finally, don’t install a rain sensor in an area that doesn’t receive precipitation, such as an enclosed courtyard with a skylight or one with a sizeable overhang, Sigsworth advised. To avoid creating a problem spot, contractors should bypass the rain sensor on any zone with these considerations, he said. Especially with larger or more elaborate irrigation systems, contractors must consider the individual needs of each zone, he said. “You’ve got to manage each zone as a system inside of a system.”

AN EFFORTLESS SELL. Since rain sensors operate on a premise that’s difficult to argue with – water conservation and financial savings – they’re usually not a tough sell for contractors. Gunter started selling them with great success about a decade ago.

“I was driving down the road one day and saw somebody’s sprinkler running in the rain and I thought, ‘That’s pretty stupid,’” he recalled. “So I went to the door and said, ‘I can put a rain sensor on your system that will cause it not to run in the rain.’” Gunter sold a rain sensor that day.

Sigsworth has used a similar approach with his customers. “I’ll walk up when it’s raining and ask, ‘Are you tired of seeing your system run in the rain?,’” he said. “It’s such an easy idea, they try to put money in my pocket before I get started.”

For Standley, the issue of cost control is his biggest selling point with commercial properties. “They always want to look for a way of saving money,” he said.

Gordon agreed, adding that there is such a clear economic argument for using a rain sensor. “If I can install a $35 device and pay for it after about 10 waterings, it’s real easy math,” he said.

The author is Associate Editor of Lawn & Landscape magazine.

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May 2000
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