In a quandry

Hi! I have been using Flex Daily for several months now, and the yard is doing great! I have a strawberry tree in the backyard that has always struggled. The new leaves would burn, and the growth was very slow. This summer, the tree is shooting up, the leaves are green, lush, and full, and it has more flowers than I have ever seen! I’m seeing the same results with a ceanothus “Ray Hartman” in the front yard… more growth, lots of healthy leaves. Everything is doing great!

So what’s my problem? I think it’s using a LOT more water than I used to, based on my recent water bills. Which is probably accurate, since in the past I basically watered just enough to keep the lawn from dying, not enough for it to thrive. And now, the goveneror is asking for us to reduce our water use, and I am feeling a little guilty about using so much water to keep non-desert plants alive in a desert environment. So, should I keep the settings the way they currently are, or try cutting back the water a little? And if I wanted to cut back, what’s the easiest way?

Cut back on the lawn and garden areas to the point they just survive and water the trees separately?

This article has suggestions for tree watering: How, When, and Why To Water Trees Effectively

If you’ve mulched around the trees, you could even put soaker hoses on their own zone, under the mulch, to automate it.

Keeping all other settings the same, if you reduce Allowed Depletion to 10% it’ll water less gallons per month. However it’ll water more frequently. You’d think it would end up using the same amount of water regardless and only change the frequency, but my math is showing otherwise. I may be wrong but messing around with my spreadsheet right now. By my calculations, AD @ 10% reduces gallons per month by almost 50% compared to AD @ 50%, probably because it technically would need to run multiple times everyday but flex daily only allows once per day. Interestingly though (comparing to AD @ 50%) setting AD @ 20%, 40%, 60%, 80% actually increases monthly water usage, AD @ 30%, 70%, 90% is about the same water usage as AD @ 50%. I’m not sure why that is. But AD @ 10% appears to reduce water usage substantially. I think AD is the only setting to mess with in flex daily if you already have your zone fine tuned for nozzle rates, root depth, etc.

Honestly though your best bet if you feel guilty is disable your flex schedule for lawn zones and run fixed like you used to while reduced watering is being requested.

Tto reduce water usage, the first thing I would try is to reduce the crop coefficient. You might reduce by 5% to start with, and depending how your grass/shrubs respond after a month or so, try reducing further. I would reduce gradually to give time for your yard/stubs to adjust. I would be more cautious with reducing watering for your trees.

I disagree. Changing Allowed Depletion only changes the amount of water applied per time/day. Using Flex Daily, the Total water that need be applied over any length of time will be the total of the ET values, which do not change. Of course, if you change the value so much that it can’t keep up by watering every day, then you’re under-watering the zone (but saving water). That should not be considered the same.

To change the total water applied over time, change the Crop Coefficient (lower will decrease water, higher will increase it). As the Kc is used to calculate each day’s ET, it directly changes the amount of water required and applied.

I wouldn’t mind seeing your spreadsheet.

If I understood his comments correctly, he admitted that’s probably what his spreadsheet results reflected.

That’s probably the “right” way to do it. You could probably also achieve it by messing with both MAD and NIPH, as I did.

I copied my spreadsheet calculations for lawn zones into a new sheet so I can post it here. I forgot to delete out line 10, the second recommended watering time, it used a slightly different scheduling multiplier but overall was about the same, I forgot to enter the formula though. So when the outlined boxes are filled out that line won’t update.

lawn zone calculations

I’m still working on my drip zone calc. Its much more complex since I list every plant then average and combine everything. I’m seeing how my current setup runs for a month before I tweak it again if needed but if it works I’ll post it as well.

MAD also affects only water amount at one time, but NIPH affects everything.

To summarize the Advanced parameters when used with Flex Daily schedules (abbreviations are mine - not necessarily official):

  • Available Water (AW) is determined by the Soil type. The higher it is, the more moisture your soil can hold. There are soil tests you can do to determine the soil type, or look up your actual soil online. Rachio’s values seem reasonable.
  • Root Depth (RD) is determined by the Crop Type (grass, shrubs, etc.). It represents the desired depth rather than the actual depth. Rachio’s values seem reasonable, although for warm season grass, my Centipede grass has lower root depth and higher Crop Coefficient.
  • Allowed Depletion (AD) is a percent of the total water the soil holds to the root depth of the crop that is allowed to be used up before the crop begins to wilt. This is normally taken as 50%, but is not a hard number.

Those 3 values together (and no other values) determine the INCHES of water that Flex Daily will apply to the zone at one time/day. They are simply multiplied together to get the result:

Inches Water Applied at once = AW x RD x AD

ONLY the above 3 values determine the amount of water applied at once. For newly installed sod, you can save water by setting the Root Depth to a lower level, but always higher than actual root depth, and increase it over time to the desired root depth. And you can play a bit with the Allowed Depletion. But in general, these values can and should stay the same.

  • Nozzle Inches per Hour (NIPH) is a measure of the amount of water in inches covering the zone that will be applied in an hour. It is a critical value to the calculation of any irrigation system, and unfortunately, not easy to determine exactly. This information can be gotten from manufacturer’s charts, and by using Catch Cups. IMHO, the easiest and best way is to measure the gallons of water used per unit time for the zone and the area of the zone in square feet to calculate it by the formula:

NIPH = Gallons / Minutes / Area x 96.25

  • Efficiency is a measure of how evenly water is applied to a zone. When using a Catch Cup test, it is defined as the average Inches of the lowest 25% of the readings divided by the average Inches for ALL the readings.

NIPH is then used to calculate how many minutes of irrigation is required to put X amount of water down, usually the Inches of water at once. It is modified by the Efficiency by dividing the time by (0.4 + 0.6 x Efficiency). The idea with considering Efficiency is to over-water most of the yard in order to not under-water the lowest flow areas. I feel Rachio’s values are fine. Better values can only be obtained through use of Catch Cups, and my experience indicates that this can be so problematic with actual placement as to be almost worthless.

The only Advanced factor left is:

Crop Coefficient (Kc) is a measure of the percent of water required over time compared to an open pan of water (the FRET value). If a pan of water sitting out in the sun evaporates at the rate of 0.2" per day, and your Crop Coefficient is 0.8, it means your crop would use 0.8 x 0.2" = 0.16" of water per day. The higher the value, the more water it uses, and vice versa. FRET (Forecast Reference crop EvapoTranspiration) is calculated by the NOAA and the NWS and is published in various forms, and takes into account temperature, humidity, wind, sun, etc. Rachio calculates the total ET (Evapotranspiration) for each day from all this information, as well as the Sun setting you input for the zone.

The ET is the value that determines how much water the zone needs over time, and the only factors that determine it are the Crop Coefficient and Sun which we can set, and the weather, which we cannot.

It has been stated many times that the NIPH changes the amount of water received, and it does, but it is best if it’s calculated accurately and left alone, rather than used to change the operation. But reducing NIPH will increase the time which then will increase the ACTUAL water applied during each water application. It doesn’t change the water needed, only what is applied at one time. But while most of the other factors are based on facts, adjusting NIPH just to change watering amount is in effect lying to your system; I think that changing actual factors like Kc or AD make more sense, and using a determined-accurate value for NIPH.

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Looking at your spreadsheet, I find a couple things:

You seem to be using Efficiency twice: Once, using the square root of efficiency, to calculate a corrected PR value (which I don’t think should be done), and a second time using the standard formula to determine the number of minutes. IMHO the only place efficiency should be applied is the minutes calculation. The actual water applied by the nozzle does is not affected by efficiency. This does not change any other calculations, as you don’t seem to use this value anywhere.

You assume 4 weeks per month rather than an average number of days, but again that doesn’t change any relative numbers.

Where I think you are indicating a savings when changing values that I think is incorrect is in the rounding of the days between watering (2.3 in the example). You round that value UP to determine how often to water, when in fact Rachio would round DOWN (rounding up would allow the zone to go below zero MAD). And you can’t use the result as a real value anyhow, because it’s not constant. The first 2 times, Rachio would go only 2 days before watering, to not allow too low a MAD, but the third time it could probably wait 3 days. On average, the system will water 7/2.3 = 3 times per week or 13 times in a 30 day month (12 times in a 28 day month). Any “Savings” resulting from changing MAD or root depth would actually indicate under-watering, because the required water based on ET does not change.

@rraisley The efficiency used in ‘actual in/hr’ is just a random reference. I don’t use it for any of the other calculations, I’m not even sure now why I put that there. I only use the PR nozzle in/hr for the calculations.

For the cycles per month I chose roundup because 2.3 for rachio flex would actually be 3 days since anything 0.1 or above is counted as a day. There’s discrepancy either way its rounded though. Like if it were 1.5, in 7 days that would actually be 4 cycles, but if rounddown then it would do 7 cycles and if roundup it would do 3 cycles. That of course throws off my calculations for everything below that line. You are correct though about AD not having effect on water usage, I removed roundup and that makes the gallons used per month stay the same regardless of AD changes. @philospher77 do not listen to what I mentioned above.

Here’s the updated spreadsheet:
lawn zone calc