By Vanessa Salvia

The Western states are in a drought. That’s not news. It’s also not news that cannabis grows need a lot of water. More water is being pulled from rivers than ever, and in alot of places less water is falling from the sky. That leads to a lot of tension over water rights and usage from farmers who don’t want to compete, and from wildlife that need the water but can’t find it. A study published in February 2022 in the journal Nature Climate Change shows that we’re living through the West and Southwest’s driest stretch since 800 A.D. They don’t expect the drought to let up before 2030.

Michael Box works with Sustainable Village in Boulder, Colorado. He is the lead designer for all their irrigation systems. Box has been in Boulder for 22 years working in the world of organic agriculture. He entered the cannabis realm in 2008 and was formerly part owner of a large-scale medical facility. Back in 2011 he helped build the first legal greenhouse in Colorado. 

“I’ve always been fascinated with plants and how they grow and, the real thread of all that which I have followed, is irrigation,” Box says. “I just happen to have a fascination with water in general. I’ve closely followed a lot of irrigation work around the world and for most of my life.”

Sustainable Village’s founder Steve Troy has been working in the appropriate sustainable field since  1967. Troy designed and sold products and systems that were efficient and effective for their intended usage in developing countries, in order to save kilowatt hours of electricity, gallons of water, and keep pollutants out of the atmosphere. Sustainable Village sells sustainable products for homes, farms, and gardens, including cannabis. Box says large-scale and living soil and native soil cannabis growers are the types of clients they love to work with.

Their roster of irrigation products includes Blumats plus tools and accessories for drip irrigation. The Blumat technology is a sensor that automatically supplies plants water through thin tubing. It’s a ceramic cone that employs the principle of hydrostatic pressure, which delivers water extremely slowly, and at the plant’s own preferred rate, allowing each plant to determine its own irrigation schedule. This technology is highly effective and reliable, which helps create ideal plant growing conditions without the use of electricity. 

Water conservation means using our limited water supply wisely. By implementing basic water conservation techniques, you are able to save thousands of gallons of water each year. Image by @jmagilla in Washington state.

Water monitoring
The way we have delivered water has changed a lot over time and involves many methods. Field flooding — essentially diverting water out of rivers and channeling it to flood a field with it—is still frequently done in developing countries and even in the US too. But we now have access to technology that provides more efficient and precise water delivery methods.

“The things I like to see in irrigation are simplicity, low energy called, and sensitivity to the environment,” explains Box. “We’re really shooting to maintain static moisture levels and never over water, not underwater, but provide just the right amount of water at the right time.”

That involves monitoring, and there are different ways to go about that. In areas that have been experiencing drought and irregular weather patterns, including Colorado, they often get water from precipitation when they don’t need it, and not when they do need it. Even large-scale cannabis farms can improve efficiency by using monitoring systems to make sure the right amount of water is being added when the plant needs it. 

Drip irrigation 

For large fields, drip irrigation is commonly delivered through rows of drip tape stretched out in long runs. Box says drip tape is 90% more efficient than flood irrigation. “From there, we can step into even more efficient models that will last longer, that are made out of products that are more sustainable, that don’t need to be replaced as quickly, and that use less energy to pump and power the water system,” Box says. 

Most of the growers Box encounters are producing cannabis either at home or in larger scale productions, and both are usually growing in some sort of container like a pot or a raised bed, although some are planting right in the ground. “When we grow cannabis in a container, the goal is to maintain a really consistent master level of soil that is not too dry, not too wet,” Box says. 

Maintaining an optimal moisture helps all the biological activity in a soil growth media like beneficial bacteria and fungi. “Those are living organisms and their living environment is soil,” explains Box. “When the moisture levels fluctuate dramatically it disrupts their ecosystem. Too dry and the  microbes go dormant or too wet and you can start developing anaerobic conditions and killing off oxygen breathing microbes.” 

In other words, find the Goldilocks zone of the perfect conditions, and stay there as much as possible. Proper moisture levels means the microorganisms can flourish and do their job — whether that’s to fix nitrogen, transfer nutrients, or hydrolyze phosphorus — they’ll be able to do that job 24 hours a day, instead of just when they have periods of optimal moisture levels.

“With an optional environment, what people tend to see is significant yield increases, increases in plant vigor and plant health, and resistance to disease,” says Box. “And then we’re also using a lot less water because we’re only using just enough for what the plants want without a lot of runout from the bottom of the pot.”

A big thing for any indoor production these days is reducing capturing the runoff and cleaning it, reprocessing it and reusing it so that water is not wasted. In many cases, regulations require runoff prevention, so the more you can do to optimize water usage in your grow, the better. 

Box says the moisture-sensing valves in Blumats are highly effective, which is why Sustainable Village has used them for years and built them into larger irrigation systems. These are properly called “tensiometers,” which are devices for measuring liquid surface tensions. They look like a ceramic cone about 5 inches long with a plastic top. A thin, 3-millimeter line runs through the top. It’s buried to the top of the soil line and filled with water. As the soil dries, the hydrostatic pressure (the pressure created by standing or resting water) on the ceramic tip changes, which pulls on a little membrane that opens a valve that allows water to flow. 

“These are really low tech products, quite inexpensive, and we use them as valves to control a watering system in a container,” Box explains. “For a 100-gallon pot with a nice big outdoor plant, you could use one of these valves and then just downstream of it, connected to that would be a Tyvec soaker hose that we like to use to give a nice, slow, even watering and raise the moisture level just enough to, to close that valve.”

Systems using these “carrots,” can be operated from pump systems or pressurized water lines, but they can also be gravity-fed as well since they operate at a low pressure of under 15 PSI. Box says some of the most elegant irrigation systems he’s seen are in the Northern California region that take advantage of the natural elevation of hills, with a large water reservoir on top of a hill with a pond or a water source at the bottom of the hill and a solar powered pump, The whole system uses no fossil fuels and can supply anything from a home grow to a large-scale greenhouse. For multi-acre projects, there are other options that use different kinds of moisture meters that tie into solenoid valves. 

The Blumat Digital Moisture Meter accurately measures the level of moisture near the roots. Allowing for a more exact measurement when applying water to plants. Image by @stinktinkie2.0.

Moisture meters

There are two main ways moisture metering can be done: a volumetric measurement or a tensiometer. A volumetric moisture meter measures the amount of moisture or water in the soil as a percent. Tensiometers, which are the technology that Blumats use, provide a measure of pressure in millibars (1/1000th of a bar) or centibars (1/100th of a bar) rather than percentages. One bar is 1 atmosphere of pressure, or about 15 PSI. The amount of water that a soil type can hold is called field capacity. Box says the cheap and common home and garden store volumetric moisture meters that are a metal probe that goes into the soil are a waste of money for most people. 

“With cannabis, the best moisture level that you want to hold is just below field capacity,” explains Box. “Once the soil hits field capacity, it can’t hold any more water and starts to drain. You can measure very small pressure changes in the soil with tensiometers, which helps you keep the level at just below field capacity.”

Different soil types can all hold different amounts of moisture depending on their composition (more or less clay, for example). So when you’re measuring using a percentage, the number will be different depending on the soil composition. But with a tensiometer, it doesn’t matter what the soil type is — you’re always going to be looking for a number that’s right around 100 millibars as, as that number is just below field capacity. 

In addition to monitoring the water in your grow, there are a couple of other things your facility can do to reduce its overall water usage impact. Instead of buying cases of plastic water bottles, use a water filter system so employees can fill their own. Install low-flow toilets and faucets, as well as waterless urinals, to drastically cut your water consumption. 

The final word

Box’s main goal is to encourage people to automate their watering systems. Not only does overuse of water waste it (which has environmental and business costs), it’s also not good for the plants. “When plants get too much water, their root exudates close up, they stop taking in nutrients in water, and sometimes you don’t even notice it, it’ll still kind of look healthy, but it’s losing a lot of potential.” (Exudates are low-molecular-weight organic compounds secreted by the roots of living plants.)

Box outlines the following scenario: A grower will overwater during flower, when the weight is setting up. Then, it may take 3 to 5 days for the container to dry to an optimal water level. Then you take it offline and that causes the plant to shut down its root system so it’s not taking in any water. There’s too much water in the soil and it takes the momentum right out of the plant’s growth pattern. You might not see an unhealthy plant, but you will see a lower yield.

“One of the key factors with cannabis production is just getting out of the way when the plant starts to gain momentum,” says Box. “You have a limited window of when they’re going to grow and how they’re going to do it. And if you can get out of the way of what the plant wants to do and don’t interfere with the momentum that it’s building, that’s going to give you the best results.”

Bottom line: Provide the nutrients the plant needs and just the right amount of water, and the support it needs as it’s growing; and you’re going to get the best quality product and your highest yields.