We're gonna need a bigger boat! Crop Coefficient for timber bamboo?


Hi, I’m new to Rachio and am migrating my 13 zone yard from an old Rainbird controller to a Rachio Gen 2. Sorry in advance for the long-winded post, but I’m really excited about getting this system set up and have lots of questions!

For backstory:

Along with all of our other junk (more questions on how to set up for a lined bog later), we have 14 different bamboo cultivars here in our garden ranging from well behaved and docile to…well…threatening is a good word for some of them.

The bamboos are actively cultivated and managed (sand-trap maintenance, fertilization, and pruning 3-4X per year depending on the weather/motivation), and are irrigated for performance and maintenance. (VERY heavy irrigation during early shooting, then tapering off as the new canes mature. In my case, I work to avoid directly watering either the wall, or the sand trap, so as to lessen their attraction to new rhizome growth.) The beds are irrigated with Techline 0.9GPH drip hose at 12" on center throughout the beds.

I’m looking for a good starting point Crop Coefficient for timber bamboo groves. In my case, at full maturity here in SW Portland, a managed grove is usually 3-5 inch diameter canes that are 45-65 feet tall at about 18 inches on center, with a max root depth of about 16-18 inches if you don’t make it angry. Simply calling that a Warm Summer Grass seems a bit disingenuous to me. Suggestions?

The picture below is of one of our combined stands for reference:

The terrace beds are dry-stack stone, oriented East to West with full Southern exposure for the lower (Golden bamboo), which provides deep shade to the less drought tolerant Dulcis and Marliac in the upper terrace. The walls themselves are between 18-22 inches deep, and are back-filled with quarter minus aggregate. There are sand traps between the walls and the planting beds that are approximately 18" deep X 15" wide.

Any and all thoughts from people who have bamboo in general, or my beds in particular would be greatly appreciated.

Thanks very much in advance for any feedback.


Odd thing, bamboo is a ryzome so technically it is a warm season grass.

Just set your root zone to 18 inches. Bamboo will handle the stress much better than most because of the moisture they store in the stem. Such a cool plant…when a specific variety flowers, they always flower at the same time, regardless of their hemisphere, that is so wild to me…


Hi plainsane, and thanks for your response!

While you’re absolutely right, bamboos can be very resilient to stress, it angers them and makes them unruly to live with in my experience, so I try to avoid it at all costs being naturally lazy as I am.

I’m trying to avoid causing Rachio to underestimate my beds’ evaporation rates, and the bamboos’ transporation rate because of inaccurate input from me.

If I startle, spook, or otherwise annoy this bamboo, it will use it’s not insignificant growing prowess to go looking for whatever I’ve neglected to give it enough of - water, sun, nutrients, unattended neighborhood pets, the usual. (Notice the newly rebuilt corner on the wall? I left 1 cane I shouldn’t have, 5’ away for 6 months with a few hot days.)

For those of us playing along at home, here’s the game:

This is my 3-year-old P. vivax bed with species and 2 cultivars:

How do I explain this plant to Rachio?

Each mature bamboo cane (P. vivax) is a 4-5-inch diameter grass that grows more than 6 inches a day for about 100 days out of what is effectively a 2 cubic foot terracotta pot of soil. A lot of plant and canopy in very little soil. (30’ Area X 18" RZ) / 25 canes = 1.8 cubic feet per cane. It’s more complex than that, but that’s good enough for baseline.

The soil is 60% 5f soil mix (33% Fine Bark / 33% Peat Moss / 33% Pumice), hand-triple-dug into panned native clay to a depth of ~48". 6" steer manure mulched on top of soil (grass snacks/moisture retention).

Thoughts on how to compensate for these walls?

The bed’s walls are oriented SE/SW and are extremely porous and HOT. They’re about 32" tall, ~18" deep, dry-stacked lump basalt infilled with quarter minus aggregate. Behind the wall is a sand trap (~12" wide / ~18" deep).

I’m just trying to understand how Rachio thinks so I don’t hurt too much while I’m learning.


Well your soil is rich in organic matter so I would use an awc of .2 for sure.

Now I’m trying to read between the lines here, I assume you want to stunt stolen growth.

I would set the root zone to 18 inches.

I would set the allowed depletion to 20%. This will require flex daily to water 3.6 inches a cycle.

I would leave the coefficient at .65 myself. I think that is pretty accurate for the grass.

The pr on your zone needs to be set to something. To get that something, take the length of the soaker tube by 1 foot (to start with).
Here is where it gets nasty. Take the length of the tube in feet and round down. I’m going to do the math with 20 foot of tube.
//pemdas rule applies here…parenthesis, exponent, multiplication, division addition, subtraction in that order
waterApplied = 96.25 * (20ft * .9 / 60) //here we are trying to get the gallons per minute and based on 1 cubic foot, coverts this flow rate to inches per hour
pr = waterApplied / length of tub.

This is what I would start with. Besides pr, I can explain why I would set those parameters if you like…

Your first run will probably be insanely long, but after that should be fairly short, if it is waiting too long to water, we adjust your allowable deplition to 10%


Hi, and thanks again for the thorough response!

It’s not so much about stunting as it is cat herding. The bamboo’s gonna do a lot of growing no matter what. I’m just trying to gently steer that growth into fewer, bigger canes, rather than down / out through the walls.

18" and 20% totally make sense, and I’ll defer to your judgement on the .65 crop coeff.

PR’s really simple for my setup - .9GPH emitter every foot, laid out in a grid for .9GPH/ ’ sq. * Remember I have 11 zones, 5 of which are big bamboos, all need water fast if there’s a heatwave during shooting season.

Rachio doesn’t like that math: 96.25 * (30ft * .9 / 30) = 86.625"/hr = Displeased Rachio, so I bluffed and said “Emitter” for the time being. Should I at least make a 5"/hr custom emitter (whatever max is), and adjust other inputs to compensate?


You need to divide by 60 as in 1 hour.

Also you should be an emitter


I knew there was a reason to show what little work I had done! I blew right past the GPM / GPH bit…Thank you!