If you search for water requirements for the average lawn on the Net, chances are you’ll see the figure of 1" water/rain per week quoted. Quite often. With little consideration for temperature or location it seems.
I’ve just ordered a Rachio 3, but I currently have a standard programmable controller, and after some research, decided to use the FRET values quoted for my area weekly by the NOAA site (https://digital.weather.gov/ then Total Weekly FRET (in) from the second dropdown). Today, for example, it shows 1.50" for my area in South Carolina. For reference, Bangor Maine is 1.15". It is my understanding that FRET (Forecast Reference crop EvapoTranspiration) is basically the amount of rain a crop (grass, hopefully, or close enough) requires in a week. Definitely different in SC than ME, as expected. In setting my system, I’ve assumed that if a “normal” lawn needs 1" rain a week, and my FRET is 1.50, then I set my Budget for 150% (I’ve calculated all my irrigation times based on actual gpm and actual square feet and number of runs per week to give 1" of water, but will refine that with the Orbit cup measurements).
When I go to Rainbird’s site for ET (http://www.rainmaster.com/historicET.aspx), it gives 0.14 for June (x 7 = 0.94") for Bangor and 0.17 (x 7 1.19") for SC, which is about 80% lower than NOAA. I’m not sure about Bangor, but our 90+- temperatures here are pretty normal, and I’ve seen FRET values up to 1.8 or so on the NOAA site.
I just received Orbit’s cup gages, and while I haven’t used them yet, I did play around with the area of the cup top vs inches of flow, and readings on the cup sides, in both ml and inches. Turns out Orbit recommends for the whole summer here in SC a total of 0.87" per week. I think my grass would literally dry up and die at only that rate (maybe not quite, but still).
Why all this discrepancy? (You don’t know, I know, they’re all different sources). But I’m concerned what my new Rachio will recommend. Based on its recommended times and the inches per minute measured by my cups, I can calculate it. Any idea what it will end up?
It’s probably silly asking at this point, but what I do NOT want to do is blindly let Rachio (or ANY system) put a completely different amount of water on my lawn than it is used to, and see after a few weeks that it’s drying up and hurt the lawn.
(Again - sorry - retired engineer overthinking things.)