Spring into Scheduling - Part 3 of 3

By Lori Palmquist

This is the third of a three-part post on irrigation scheduling. To read part two, click here, and to read part one, click here. 

In this last post of the series, I’m sharing the web application I use in my practice. It’s a tool I created several years ago to make the tasks I performed as a water manager more efficient. It’s one of the 14 web apps that I’ve created and offered freely to the public since 2010. If you’re curious about them, visit my Puddle-Stompers site to explore them all, on the Apps page. https://puddle-stompers.com/apps.php.

This particular web app is called Irrcalc. This tool takes the formulas I wrote about in part two of this series and applies them directly. Whereas the two scheduling calculators in part one were for the general public or the lay person, this tool requires that the user have at least a moderate understanding of the values that go into the scheduling formula.

Following is a screenshot of the Irrcalc app, which can be found at  https://waterwonk.us/irrcalc .

Changing Up Monthly Schedules

I like to change irrigation schedules monthly for controllers that are not smart controllers. The way I use this tool is that I enter up to five zones at a time for a given month, then take a screenshot of the results and email it to the person in charge of programming the controller. I copy myself on the email so that I have a record of the schedule, in case there are any questions at any time.

The parts of the formula the tool asks for are weekly ETo, plant factor, precipitation rate, and D.U. (distribution uniformity or coverage). I covered all of those elements except for D.U., in the previous post. I’m not going to go into D.U. in this post, as it’s a deep subject that merits its own post, which I’ll do someday. Let me know in the comments, if you’d like me to address it sooner than later. What I suggest you do in the meantime, if you use this tool, is just enter 1.0 in the D.U. column, unless, of course, you truly DO know what the D.U. of the zone is.

If you don’t know the weekly ETo, the plant factor, or the precipitation rate, you can get these values by clicking the image at the bottom of each respective column. Clicking the image will launch a popup that will provide default values. For the weekly ETo, I’ve only programmed in five Bay Area counties - Alameda, Contra Costa, San Francisco, San Mateo, and Santa Clara counties. If you’re in California, but not in one of these five counties, you can go to  https://waterwonk.us/weekly_eto.php.

What’s the Value of a Good Base Schedule?

The Irrcalc tool is also good at calculating base or “peak” schedules. A base schedule is the schedule for the hottest time of the year. Many smart controllers require that you enter in a base schedule. And then the smart functioning of the controller adjusts the schedule for every day that is not the hottest time. Here in California, our peak schedule is usually July. In some places it could be June. But more commonly, July is peak month.

One of the shortcomings I see with using this type of smart controller is that so many people don’t have the knowledge or skills to create a good base schedule. It’s that “garbage in, garbage out” idea. You need a valid base schedule so the weather-based controller can truly be efficient in its functioning, saving water and keeping the plants healthy and happy.

If you create a good base schedule for a smart controller, it will then adjust either the run time or the frequency of watering for the times when it's not peak season. Most smart controllers that require a peak schedule will adjust the run times. Some of the newer controllers will adjust the frequency. And a few of them will adjust both.

The other strategy for smart controllers is to have you enter in the data for each irrigation zone. This often includes the plant type, exposure, the irrigation device, the soil type, wind, and slope. But I’ve noticed that controllers with this strategy are disappearing from the market. They are few and far between. The most popular strategy by far is to adjust a base schedule.

That’s All, Folks!

This concludes my posts on irrigation scheduling. I hope this has helped you gain deeper understanding and that you’re eager to put your knowledge into practice. I wish you a glorious spring and happiness in the garden. Hug your favorite plant for me.