It just isn't smart

Set your root depth to 4 inches and your allowed depletion to 50.


@runner1717 is right but which specific grass do you have, I think you need to be at a 6 inch depth.

Maybe too much water and fertilizer take makes Brown patch decimate a lawn. Only a few products that will prevent or halt brown patch - Headway G and Pillar G and these are commercial products that sell for about $85 for a 30 pound bag. I bought mine online.

Sounds to me like your lawn is not very healthy currently. You say you need to water twice a day during the heat, but the Rachio is correctly setup to run once per day. You need to train your lawn to grow a longer, healthier root system. My guess is your roots are about 2 inches right now. Keep your current setup, but slowly increase your root depth every few weeks. You may need to add a fixed schedule for the same zones that runs later in the day as you have ‘trained’ the lawn to take water like this, but a healthy lawn really should not need a double watering. Have that fixed schedule run daily while it is very hot, but after a week, switch it to every other day, then remove it as you increase the root depth of your lawn. Are you sure your soil settings are correct?


I think you have nailed it. The combination of shallow root depth, Sandy Loam, and 30% allowed depletion appear to have conspired with Flex Monthly to underwater your zone. Assuming you have the irrigation rate correct for the rotor type (if you’re not sure, you really need to check this), I think you should change to Flex Daily and increase your root depth, first to 4" then back to 6". Flex Daily would adjust more rapidly to the high usage rate your chart shows. At the very least, you would be able to see what happens. As it greens up, you may even be able to back down your crop coefficient (but I would do that last).

Good luck!

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I have already tried previously before the Iro to water less often, this results in the whole lawn drying out and wilting.The reason we need so much water is because the soil is extremely sandy, especially because we’re on a beach here and the natural substrate is all pure sand. The roots simply do not grow any longer, I suppose they may be 4 or 5" some places, but in the most troublesome spots of course they are not. The heat kills the grass before it can really establish itself very well each season, it seems.

Its a Canada lawn mix, I am not sure exactly, because seed was added multiple times, so its pretty much a mix of all sorts of grasses. Probably things like perennial rye, creeping fescue, etc.

Definitely not too much water, as the grass and soil feels bone dry on the hot days. Literally you can pick it up and its dust-like. That’s not normal for lawn soil. I know it seems unlikely when you have nice soil, but here with how sandy it is, we need lots more water to keep a lawn alive during hot weather. When it cools down, it does great with less watering.

You’ve got the Allowed Depletion set very low. Setting this value to 30% means Rachio will allow the available moisture to decline all the way to 30% before watering starts. It also looks like when Rachio runs, it’s running for very short durations.

I would raise Allowed Depletion to 70% and see if that makes a difference.

Can someone confirm this? From what I understand the allowed depletion works in the other direction - ie. 30% is actually water more often, not less often. Is that not the case?

You are correct. Lower depletion means more frequent (and shorter) waterings. That’s one reason why I would consider increasing the root depth and go to Flex Daily: you could see if it projects daily, longer waterings given your sandy soil.

Yes, “Allowed Depletion” is how many percent away from 100% (fully saturated), before watering should happen again to refill.

From your settings, it looks like you are trying to “game” too many settings at once. AFAIK, Cool Season Grass should have a Crop Coefficient of 0.70. I would suggest keeping it at that, unless you really have vegetation consuming more water. Same with Root Depth, you really need to figure out your average root depth properly. 3" vs. 4" is a huge difference, percentage wise. Even more so with 3" to 2", if your grass has virtually zero grip due to previous schedules.

If you have a fairly good head-to-head coverage, your efficiency should be higher than 50%. Turning this too high would put down more water at once, without any added benefit. Given your soil type, it would probably just go further down, away from your roots and add zero effect.

Really the only key factors should be:

  • Available Water, which must be very short, since as you say, you have almost sand like soil.
  • Allowed Depletion which probably could be even shorter 20%, on a Flexible Daily schedule of course.

However, I think there must be a calculation error in the Rachio, which may be triggered when switching weather stations:

Looking at your Moisture Levels chart, on July 21 & 22, the Rachio put down 0.19", which is the same as your evap. ratio = steady moisture balance. However, on the day you switched weather stations, it put down twice as much as your normal evap. ratio, and then skipped a day. Almost like it did a “soak” due to the change, and though there was more than enough for the next day. However, with your Available Water set to 0.1, the overshooting moisture should not be accounted for, and as such, the next day should start fresh at 0.10" as 100% moisture level and the expected evap. ratio to ~0.19"…

I’m also curious as to why Rachio is reporting 0.10" as 111%, if that’s your Allowed Water setting? That would be 100% then, and not 111%.

So, it’s clear that you with a Allowed Water at 0.1" and a evap. ratio of 0.15-0.19 are trying to get your sprinklers to run twice a day. But that won’t happen automatically I guess, since the Rachio only waters once a day on the flexible schedule.

My only suggestion to that would be to enable an additional fixed schedule which you run whenever you want, to compensate; and which you turn off as soon as the temperature creeps back down to normal levels. Maybe there’s some IFFFT integration you can use to take over on the “bad” days?..

If this is pure sand, add a lot of organic matter to increase the water holding capacity. If grass won’t grow look around and see what native species do. Sounds like you are fighting an uphill battle. I don’t think Rachio is for you.

It is soil over pure sand, the lawn is not growing directly in sand, but it gets mixed in and also the drainage is really good. We are working constantly to improve the soil layer, but we still need more watering. If I can do it manually, why can’t the Iro do it?

Obviously, if you are willing to run non-flexible schedules, you can make it do whatever you want. However, as far as I know, the flex schedules are not designed to run twice a day, no matter how you game the system with advanced variable tweaks.

So, back to my suggestion, add a non-flexible schedule which you enable just for the periods where you really do require twice a day watering. And turn it off as soon as your daily evap. ratio doesn’t surpass your Allowed Water level by ~2x.

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How deep does the sand start?

If it is 3 inches down, I would lower awc to .08 or .07 and I would increase your root depth to 6 inches. Most cool season grasses can get to and pass 6 inches.