I’m sure there are countless posts on this, but needed my own discussion.
I have 4 drip zones, with around 10-20 plants per drip zone. I try to do rain bird red 2gph drippers with 1 on each plant. Each zone is a mix of bougainvilla, yellow bells, cape honeysuckle, and lantana. I have 2 zones in front and 2 in rear. I calculated 1.125 gph out of a single emitter, even though they are rain bird 2gph red. My plants are established so i calculated 2 ft x 2 ft for area per plant.
Soil is mostly clay, I did the jar separation test and I had about 1% sand, 1% silt, 95% clay, and 3% water or so. It was very much clay.
For some reason when i do flex daily, it gives me a 1 hour run time. It appears to actually not be enough because my plants get wilted. I do not have any real advanced settings on my 4 zones, and they seem to run 1 hour 11 minutes with the default settings.
Should I go in and set the exact square footage, the crop coefficient etc? I believe the available water at 0.15 is correct, root depth is 15 inches, all default though.
Where in North Phoenix are you (SE Gilbert here…)? That seems like and AWEFULLY high clay concentration for Arizona.
This thread is the BEST for calculating the drip settings. If you follow the directions, you should be able to get a PR (in/hr) that works well. Main thing to start with is dialing in your soil though, and again, I struggle with that clay content for the valley.
For reference, here are my old settings from when I set mine up. I have 1gph emitters on my shrubs, which equates to a .30 in/hr, which has my shrub zone running for right at 4h each time, but this is based of my clay loam soil (not to be confused with heavy clay).
Square footage does nothing other than calculate estimated water usage, nothing related to actual watering. 15" might be a tad deep for anything but the most established and strong shrubs. I have mine set at 12" right now, but I have a mix of well established and newer planting shrubs, and you need to cater to the more needy.
Thank you. I also realized through some of my notifications I started this process back in 2018 and kind of gave up.
I was using AI to help me calculate some of this and after testing 1 nozzle I’m getting 1.125 gallon per hour, per emitter. Using the AI math (I’ll try this spread sheet next) it was suggesting my PR was 27.05? I am in anthem and my soil map shows 12 and 44. I am in 12, and 44 is within half mile around me in all directions.
|12|Carefree cobbly clay loam, 1 to 8 percent slopes|181.9|43.5%|
|44|Ebon very gravelly loam, 1 to 8 percent slopes|201.0|48.1%|
From AI about my PR:
Step 2: Relate Output to Soil and Root Depth
The goal isn’t to dump 12 inches of water depth across the zone in 3 minutes—that’s not how drip irrigation works. Instead, we’re delivering a small volume of water (e.g., 7.2 oz per plant) to the 2 ft × 2 ft root zone, letting it soak into the clay soil to reach the 12-inch root depth over time. Here’s how:
Volume to Inches: Convert the water applied to an equivalent “precipitation depth” over the area.
Yea, that PR math doesn’t check out…at least not in this application.
If you follow the spreadsheet, it is using the inches of water Rachio calculates it needs to put down, the gph of your emitter, and the amount of gallons you should put down (from the "Water Use it Wisely guide) to calculate what the PR should be set to.
Were you able to check the soil type? I did find an error in my zones, they were bubbler, i changed to emitter. Now my drip is scheduled to run for almost 2 hours. That seems more in line with 2-4 gallons per plant per watering, while doing 1.125 gallons per hour from my emitters.
You can use the Web Soil Survey site to look up your address and would tell you what the native soil is. It is usually pretty accurate, however with large subdivisions, they do a lot of earthwork to the lots prior to building, so use it as a rule of thumb. What you found from AI might be somewhat accurate since it probably pulls from the WSS site…
Not sure what your shrubs look like, but I usually set mine to put down about 4 gallons. My biggest “shrubs” I have stepped up to a 2gph to give them a little extra if it looks like the 4 gallons (which works on 90% of my shrubs) isn’t cutting it.
Here’s what I ended up with in Rachio after setting up soil. It’s .84 inches in the app, which breaks down to .32 PR? Hopefully that makes sense. It appears the run time is 1 hour 40 minutes per zone.
Yep it looks like AI was doing GPH instead of GPM in its math. I think changing from bubblers to emitters was the biggest help as that doubled my drip time. Now to watch the water bill.
