Adjusting crop coefficient monthly?

So I read this article:

For my cool-season lawn in Northern California, would it make sense to adjust the crop coefficient for my turf zones on a monthly basis based on that chart? Or am I going to be dumping way too much water since Flex Daily waters based on the daily ET balances, which go down quicker when it’s warm out?

Also, why the heck is April 1.04? :slight_smile:

Isn’t the Rachio’s “intelligence” supposed to compensate for things such as temperature, humidity, and wind in calculating plant transpiration?

Yeah that is basically my question. I know Flex Daily does adjustments based on the local weather, so I was wondering if increasing crop coefficient in line with the chart during the warm months will just over-water my lawn.

If the Rachio is doing what it’s billed as doing, I would imagine so.

Rachio does not adjust crop coefficients monthly at this time, only a number of weather variables to calculate adjustments.

That kind of variation is just too complex to consider for a home. I’m surprised they even have that table for Warm Season Grass, when there is more variation between one type of warm weather grass and other (my Centipede versus Bermuda, for example), than the monthly variation shows. Such variation can be critical in farming, where hundreds or thousands of acres can result in huge amounts of money being wasted, but even looking at this non-specific table, there are some potential problems: Like April, May and July Kc all higher than June Kc. Variations like this can and do occur, due to stages of growth, like seed production, dormancy, etc. But in the end, for residential lawns, a single value is sufficient. Heck, it’s hard enough to even get specific and accurate average values for specific grass and other crops.

In the end, I think if you take actual or average values for ET over these months with a constant Kc, or with varying values of Kc, the results will be close and the complexity it would cause is really just not worth it. Most people have much higher errors in their other values for this to matter much in comparison.


Great post. Thank you!

I use this exact chart for my yard in the central San Joaquin Valley. I started doing so after @Klaus from Rachio told me they no longer support Kc calc’s in the app. I’m guessing they just “round it” so they would use that 80 figure and adjust other parameters from there — but it’s just a guess.

I can tell you this, since I started using the UC chart and adjusting the Kc on my yard monthly my water consumption dropped nearly 50%/yr and my yard stays beautifully green all year long instead of turning brown in the summer (fescue-cool season grass) and being drenched in the cooler months.

I just set a reminder in my iPhone and put a copy of the chart on a Notepad text file (iOS). It takes about 3- to 5-min/mo to adjust all of my zones.


Awesome, great feedback, thanks!

I adjusted my zones and I’m now putting down 2-2.5" per week, wowzers! But we’ve been at over 100’ here in the Sacramento area for almost a month now, so maybe that’s right?