How long do you run your controller for?
It’s amazing how often I walk up to an irrigation controller and look at how long each station is scheduled to operate. Regretfully, it’s more of the norm to see spray heads set to water 15, 20, even 30 minutes every day, applying up to an inch of water, when they only need to run 6 or 7 minutes per day.
So how long should you run your systems: Today, most spray-type sprinklers apply 1.5” to 2” of water per hour? The average evaporative losses on Oahu are about 0.18” so on an average day, in theory you need to irrigate less than 7 minutes per day to replenish the full ET. However, not all plants need full ET and not all areas will be the same.
A protected shady area of your property may only have losses of 0.12” or less while a dry, windy area that exposed to full sun will be higher. Each plant type has a different crop co-efficient. For example, a cool-season turf grass may have a crop co-efficient of 0.9 to 1.0 which means it needs 90% to 100% of ET to survive. Warm season turf grasses however are happy with 65% to 75% of ET. Like most hard wood shrubs only need 40% to 60% of ET, but tropical ornamental plans can be as much as the cool season turf.
We also see most controllers set to irrigate every day or every-other day, but is this best for the plantings? Perhaps, if it’s a sandy well-drained soil, but most of Hawaii soils are clay or loam soils which would be better to irrigate every three or four days. The trick is to water deep enough to encourage the roots to grow deeper. This not only allows for healthier plants, but will also allow the soil to act as a reservoir to supply the root zone during drier periods.
Computing this out can be difficult, but there is new technology, which will allow it to be automated in the future.
In the 1920’s the first irrigation controllers were introduced into the marketplace. These were expensive and did little more than turn on or off the valve at a given time. While crude, they were an improvement over the manual night watering man, it replaced.
Today’s new “Smart Controllers” do so much more and can actually pay for themselves in water savings within the first year.
Typically these new controllers use either on-site data, from NOAA stations or from soil moisture sensors, to collect the data for the site, and then automatically compute the run time for each station, based upon the actual site conditions.
Initially when you set up the controller, it does take slightly longer, as you must supply the controller with some basic data. The basic set-up includes programming in the sprinkler type for each valve (sprays, rotors, drip), the plant material you’re irrigating (turf, shrubs, trees, etc.) the soil type (clay, loam, sandy) the solar exposure (full sun, part sun, shade) and the slope condition and the computer automatically will program each station on a daily basis, depending upon the actual climatological data for the site.
For those desiring to even save more water, you can do advanced programming to customize the actual precipitation rate, the desired root depth of the plants, location on slope (top of slope needs more water than bottom of slope) and the amount of effective rainfall you want the controller to utilize.
Historically, these Smart Controllers save anywhere from 30% to 50% of the amount of irrigation used on a site over conventional control systems.
As with any controller, the cost of the controller varies depending upon the brand and features, but we’ve seen eight-station models with a list price of less than $200 on up to very sophisticated versions which sell for twice that or more. As with anything you would get more features with the more expensive ones, but even the less expensive models will save you money.
Today, you can hire a professional to program your irrigation system and then retain him on a monthly basis to fine tune it as the climatological conditions change….or you can use a Smart Controller, which easily walks you through the programming and will save both you and your client money.
Mr. Schildknecht is the President of Irrigation Hawaii, Ltd and is a Professional Member of the American Society of Irrigation Consultants (ASIC), an Irrigation Association certified irrigation designer (CID), Hawaii’s first EPA Water Sense Partner.