NEW Dynamic Crop Coefficient feature

Hello all, we’ve just released a new feature we call Dynamic Crop Coefficient, and we’re excited to already see interest in the feature. We build this in part using feedback from the community in these forums, so I’m posting this here as a starting point to get more feedback from the feature as customers use it.

We’ve written up an FAQ document that will address many of your questions, here: Dynamic Crop Coefficient FAQ

Beyond the FAQ, I’ll take some time here as to address specific questions that have come up in the community.

In a nutshell, this feature generates a new crop coefficient (Kc) value every month for all crops, for every zone. When you turn the feature on, you’ll get that value for your zone and cannot edit the value. You can toggle the feature on and off as much as you like. The values are local to your climate, and will change every month.

Our hope is that this feature will help avoid the heat-stress problems that many customers experience in peak summer. If you think about a sinusoidal curve vs a flat line, it’s clear that the static Kc values we used to provide were really only accurate some time in Fall and Spring, and were likely leading to over-watering in the shoulder seasons and under-watering in summer for a lot of controllers (they did for my yard).

The Kc values for turfgrass are regional, varying by high-level climate types, for example a mediterranean climate on the west coast will have different values that steppe/ semi arid climates in the Rockies, southwestern deserts, eastern humid regions, etc. I’m sorry I can’t be any more specific at this time.

The Kc values for garden-type crops will vary slightly across even smaller climate micro-regions, roughly the size of western counties. This is because we fit expected growing season Kc values to the local growing season timing, and we can do this at a finer spatial resolution.

Data sources: we compiled the Kc curves for turfgrass from peer-reviewed research where available and other academic published documents (Master’s theses, Ag school department materials, etc) where needed. For other crop types, like vegetable and flower gardens, we’ve taken average seasonal values from the U.N. Food and Agricultural Organization (FAO) tables, which are extensive, and fit them to the local growing season (link to FAO tables is in the support document).

You have already provided some great concepts for improving this feature. To get this to market quickly we did not build an offset or an enter-your-own function, and those are good ideas. If you want to apply an offset this season, you can activate the feature on the first of the month, note the value, turn the feature off, and set the value with whatever offset you want. I realize that is a hack, and we really want to learn about the appetite for a feature like this so we can plan follow-up features.

You have also identified other changes made the user interface. We combined the ‘Annuals’ and ‘Perennials’ classes into a ‘Flower beds’ class. It turns out a lot of customers didn’t know what those really meant, and even for those that do, our garden aesthetics often combine them. The root zone depth and Kc parameters for this new class is close to the average of the old classes, erring a bit on the side of more frequent watering. We have also made under-the-hood changes to “vegetable garden”, which will water more frequently, and changed “xeriscape” to “desert-adapted”, which will water less frequently and is a great choice for native steppe and desert plants that are becoming popular landscape elements in the southwest. In addition, if you set up new zones, you will find a cleaner and more informative zone setup process that we hope will lead customers to get it right more often the first time.

It’s worth saying that some of you have a really good intuitive and data-driven handle on how to tune a Rachio controller to get optimal results on your yard. We designed this feature as a finely discretized, yet generalizable solution that will work for most yards, most of the time. It could be that what you’ve learned through research and trial and error works better for your yard, and if so, keep doing what you’re doing! And please let us know if when you find discrepancies; we’re committed to improving this feature and we want your feedback.


I am really excited to see how this plays out! Previously, I didn’t do monthly adjustments, but I would make adjustments 2-3 times a year to account for winter/summer needs here in Arizona. It was clear that the Kc values were an “average” of sorts, and summer needed a bit of a boost, especially years when we had LOOONG stretches of 110+ degree days.

This is a followup to what I posted previously related to a “crop quality” offset to the new Dynamic CC feature. Texas A&M is looked to as the horticulture expert in our area as they have been involved in agriculture research in Texas longer than anyone. Below is their statement on Crop Coefficients, in Texas, for turf grasses. (See ET and Weather Data → Turf Coefficients at for source.)

First, note that the starting Tc of 0.6 is a lot lower than the one picked by the Rachio Dynamic Coefficient feature for my area (0.8). Second, note the statement that the Tc remains constant throughout the growing season for established lawns. A&M recommends no water during the dormant season for warm weather grasses in my area. Rachio might want to somehow work with Texas A&M when developing their “proprietary” settings.

Lastly, see the quality offset (Qf). This is the offset that could be added as a feature. Using this table, I set my Crop Coefficient at 0.36 for my Bermuda/St Augustine lawn during the growing season. This seems to pretty much put me in line with recommendations from A&M’s “Water My Lawn” update service.

Below is from Texas A&M:…

Turf Coefficents

Potential Evapotranspiration, ETo (also abreviated as PET), is an estimate of the water requirements of a 4-inch grass growing in a deep soil under well-watered conditions. A turf coefficent (Tc) is needed to relate pET to the water requirements of a specific turf. For established lawns, the Tc remains constant throughout the active growing season of the grass. For warm season grasses, such as St. Augustine, the Tc is 0.6 throughout much of the year, while the Tc for cool season grasses, such as rye, is 0.8.

However, we seldomly apply this amount of water to lawns. Why? Because we do not want maximum production of grass clippings. Instead, we want to maintain a healthy, attractive turf with as little water as possible. Thus, we modify the coefficent by specifying a Quality Factor.

The complete equation is:

ETo x Tc x Qf = turf water requirement

Turf Coefficient Values (Tc)

Warm Season 0.6
Cool Season 0.8

Quality Factor (Qf)

No Stress 1.0
Low Stress 0.8
Normal Stress 0.6
High Stress 0.5
Very High Stress 0.4

This sounds like a great idea. Guess we’ll see. My concern is that while Rachio recommended 0.6 Kc for warm season grass (I’m in Columbia, SC), online sources recommend 0.85 for Centipede grass, which is what I have. I’ve used that since getting Rachio, and if anything, I think I’m overwatering.

After implementing the variable Kc feature in Rachio, it moved what would normally have been the 0.6 Kc to 0.8. And you say you expect it to be higher in the summer. That sounds like it’s going to be a lot of water.

It’s also a bit confusing for the default warm season grass that your year-round value was 0.6, but it’s already set at 0.8 and will no doubt get higher. I’ve been told by lawn guys that I greatly overwater my lawn, but it sounds like Rachio will advise more, not less, in the future.

Can we obtain any of the variable grass Kc data throughout the year, to anticipate how this will affect our water usage?

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My comments (and source of information) are basically in line with what tlight posted.

I was excited to see this feature but when it jumped the Crop Coefficient from the 0.6 I set straight to 0.8 which is as high as I would ever go when we get several weeks of over 100 deg F in August I’m afraid it is not going to work for me. Right now is our ‘rainy season’ in North Texas :slight_smile: We are permanently in some form of drought so overusing water is definitely not desirable.

I understand an awful lot of work has probably gone into this but I don’t think it can realistically cater for all the microsystems. Truthfully, having a single setting for warm season grass is not ideal since Bermuda, Zoysia, St Augustine all have differing needs which themselves differ in different areas - even in the same state. For my needs, a simple table where I can set (or override) the coefficient for each month would be more useful.

I have had my Rachio turned off all winter simply because the Bermuda/ Zoysia is dormant and the rain we get is adequate during the winter months. The aim (for me) is to apply just enough water to keep the lawn healthy without over-watering and wasting a precious resource.

Sometimes I think moving away from the Flex Daily and setting a Monthly (optimistic) schedule might work better for me. Then, if we don’t get the expected rain or the grass starts to look stressed I can just do a manual water to play catch-up.

EDIT: Which reminds me of something I have seen suggested many times which is a simple water more/less slider. I play with the coefficient which has to be done on each zone. It would be great if I could just reduce the intelligent watering at the top level by 10 or 20% most of the year and then increase it in the heat of summer.

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This would be a GREAT FEATURE.

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Okay, since the dynamic Kc is built into both the mobile apps, but NOT in web app (which I prefer using), I need to know what, if anything, I should avoid doing in the web app so as to not screw up the dynamic settings. Can I VIEW everything? But maybe not CHANGE anything? Or can I change things, but not the Kc value? I’d really like to know what my system is going to do. Any my other concerns and questions and concerned above have not been answered.

Hi @rraisley, as a general trend we are not going to support new features in the web app, but you can still use it to view schedules and make adjustments that aren’t related to new features. For example, adjusting crop coefficient might get confusing since you won’t be able to see the DCC functionality, however you could adjust exposure, efficiency, or other advanced settings without any trouble.

Might be the most disappointing thing I’ve read on this forum. Do you mean the changes will lag behind those of the mobile app, or the decision has been made to stop development on the web app all together? If the latter, I’m going to be very disappointed.

One of the great things about Rachio is the ability to make changes on both the mobile and web apps. i don’t think I’m alone when I say I prefer to make changes, especially big changes to many zones, on the web app. Having to do that in the future on the mobile app is not going to be fun.

Please tell me it ain’t so…

I agree with tlight: I really prefer using the web app, because I’m on my computer all the time, and with the larger screen, etc. it’s easier to use, I can do screen captures for use with the forums, etc.

drew_thayer concerning the DCC, can I get a listing of what the Kc values will be for each month? I can then use those to make my own table to change manually to. And do you think that the table applies to Centipede grass as well?

The reason I’m asking, is that I find the water adjusting (Adaptive Watering) feature pretty much worthless. I WANT/NEED to water my lawn less than it currently is. But messages like “No adjustments made since last watering” tell me nothing. If I set it to Water a Little Less last week, does it still say that, since I haven’t adjusted since last watering? How much is a Little? How much is a Lot? Are they additive? (We were told they were, but they don’t seem to be.) There really needs to be documentation on this major feature. But really, why can’t a single slider and/or text field be used to add or reduce flow in say 5% increments?

Without a better water adjust feature, the only way it is possible to change the water applied to my yard over time is to manually change the crop coefficient. Which I can do, but would like to know what Rachio would set it at, so I can go say 15% lower than that. That’s a pain, but something I could do, once a month, if I knew what the table values were.

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@rraisley I appreciate your critique of the Adaptive Watering feature. We share a lot of the same critique and we are working on gathering feedback to improve the feature, or possibly replace it with an adjustment feature that is based on crop coefficient, as you and others have suggested here.

I realize this is an annoying answer, but I can’t share the Kc value tables for all regions for every month right now. However, if you want to offset from our recommended value, you can toggle the feature on at the beginning of each month, note the value, and set your own. We realize this is cumbersome and not ideal; again we’re gathering feedback as best we can right now to choose the best improvement to the feature.

@twin1 @tmcgahey @rraisley @tlight @gweston @championc @ECOBEARD

Hi, to all that have been active in discussing this feature, today (May 24th, 2:30 PM MDT) we needed to make a system-wide adjustment that re-set Dynamic Crop Coefficient for all controllers into an OFF state. You can simply turn it back on in the settings of any of your zones, and you can select “apply to all zones” to re-activate it for your other zones if you wish. No changes have been made to the functionality of the feature. Sorry for the inconvenience.

I hope you are all experiencing success with your irrigation this spring. In Colorado it’s been a strange season with an extremely dry and windy April due to La Nina weather patterns, followed by a very wet period in May that even had us flirting with frost temperatures last week; it’s kept us on our toes. This is the earliest I’ve turned my system on in several years. Cheers.

And, in the last 5 days, you got snow…

I appreciate that, and considered doing it the way you suggest.

In the meantime, you should at least be able to share by how much “Little More”, “Lot More”, “Little Less” and “Lot Less” mean? That may give me the same functionality I need; I just need to know more about how it works, and as a “completed” feature, we should have a complete explanation for it.

Thanks for telling us about turning off Dynamic Crop Coefficient. Too bad the 99+% of Rachio users that don’t visit this forum and/or didn’t see this post don’t know that.

I am a bit late to this new feature party, so I apologize if I miss something that has been previously posted. As a geeky engineer type, I am all for tweaking things with more advanced AI like variables, but also know the value of manual observation and corrections.

My thoughts:
Assuming one has done a good job of dialing in the root depth and watering rate for their soil type for each zone, unless we have tons of adjustability and fine location data for the individual crop every week of the year, we are sort of stuck with cramming a lot of variables together. That is why we try to use evapotranspiration (ET) vs transpiration and evaporation separately. When in doubt, it is easiest to error on the more vs less water and end up with a healthier lawn. The hard work is achieving 90% or 80% of that ideal lawn with far less water per year. Personally, this is my goal here in California. One key to that is letting the grass grow longer as summer approaches to shade the soil and drive deeper roots, without letting it fall over (stay vertical). I use a power rake a few times per year as well as some back breaking Groundskeeper II manual work in smaller areas. Another is staying on top of grub so that there are more and longer roots to draw from a deeper root water zone. Another is using a high lift blade in your mower.

It appears that this dynamic crop coefficient is actually convoluting ET and transpiration. The Rachio engine claims to do ET in the back end, but is basically a fixed ratio of evaporation (wind, heat humidity). It does little to deal with transpiration through the various plant cells and out from week to week. How could it without a big table of optional crops, not to mention that the end user would need to have single crops per zone, just like they already need single root depth per zone. What I thin Racio does is attach a single variable to crop coeffect (Kc) for each of the various crops chosen in the filed before the advanced field (ie cool season grass vs warm or shrubs), but then that is convoluted in with the root depth.

I am totally on board with @tlight post on a quality variable. What we need is a simple per zone correction to the crude ET calculation based on a base crop type (daily evaporation*fixed crop type month to month). This is even a good way to advanced menu handle shade and slope changes per month. If we go hard core to water rationing, what do I do to have barely alive grass for a couple of years with almost no water?

Last thoughts: When we add in fruit trees, we have a totally different situation on watering than for turf. First off, you cant do a good job mixing a 4-5 inch root depth grass with a 12 to 24 inch tree root depth. Second, stone fruit needs a lot of water during fruit development but not usually during the hot moths of the summer. Those fruit development months in my area are at the tail end of the rainy season until June, where the water requirement goes up by 7x to 12x, then back down to ¼ of what it is in May-June, just a month or so later in mid July and August months.

Not sure I agree here. All “crops” from grass to shrubs, to trees (fruiting or not) will actually have different Kc (crop coefficient) depending on the time of year. Rachio is just trying to tap into that rather than leaving an average Kc value (albeit user adjustable) for each plant “type”. You are 100% correct that even people with zones spilt between trees, shrubs, grass, etc will have specific plants within those vegetation types with differing Kc values. Unless you are in the Ag world, you probably aren’t going to have singular crops, so you still need to kind of need to find the best middle ground.

The root depth controls the duration and/or frequency of water. You need to keep the soil at a certain moisture level at the root depth…

Again, in any case, this isn’t the best situation. Ideally you should have grass, shrubs, and trees on their own zone. If they aren’t, you really need to play towards the most needy, and the others will have to make due. This isn’t really a Rachio issue, as much as it is an irrigation system design issue…

Crop coefficient, which determines how much water the crop needs over time, has nothing to do with root depth. Root depth helps determine how much water is applied at one time, as does soil type and allowed depletion. Crop coefficient helps determine when to water the amount previously calculated to keep the moisture level within allowables.

Hello bug99

Are your familiar with the Penman-Monteith evapotranspiration model (PM)?

I am not yet certain to what extent Rachio has implemented the algorithm because I’ve only recently setup my first controller. But lets assume they have rigorously done so.

Then, all parameters for the flex daily schedule correspond to parameters in the PM equation which was originally derived for clipped cool season grass (12 cm in length). The Kc parameter was later added to the equation to compensate for other crops’ transpiration efficiency (relative to grass).
Kc is merely a factor to ET0 and does not convolute the equation at all.

The actual determination of seasonal Kc is a whole scientific subject of its own and I am curious where Rachio gets its data from.

Root depth on the other hand does not enter the PM equation at all but is used for determining the soil volume accessible to any given crop type. Deeper roots translate to a bigger water reservoir which translates to fewer irrigation events but longer irrigation duration.

Cheers, Sebastian

@wpd84 I am not familiar with that document. It is thick, but as i glance at it, I believe that it goes into detail on the calculation of a baseline ET, then corrects it with a simple Kc, as we are doing here, for the various crop types as they differ from that baseline. I am not sure that it deals with changes in Kc over time and conditions (changes in the specific plant from week to week).

Perhaps the way i referenced root depth above was unclear. I was not trying to say that it was included in the ET calc, but rather that the app picks several baseline values on the screen before the advanced settings screen when you pick the crop (ex cool season grass), one of which is root depth, which can be manually changed on the advanced screen. I suspect that several other values (variables) are also chosen that we cant manually change in the advanced screen section when the crop is selected.

Something that comes to mind that seems important is that we are dealing with integers, but basically calculating with real numbers. We / the system chooses to water on a particular day or it chooses not to and it waters the same amount every day that it waters. There is no 60% or 120% watering going on nor is it going to change when it is going to water on a given day or water more than once in a day, so it is a crude tool at best. It can only do so much. What it will do, if there are normally significant gaps in the days of watering (hopefully the case), it can change some of the days and the number of days that get water in a month to achieve the calculated result (integer, more with less).