By Vanessa Salvia

In Grow’s Sungrown 2022 issue, I interviewed Michael Box, who works with Sustainable Village in Boulder, Colorado, as the lead designer for all their irrigation systems. He has worked in the field of organic agriculture for 22 years and with cannabis since 2008. In 2011 helped build the first legal greenhouse in Colorado. He gave some great advice and tips on reducing water usage to not only operate a more sustainable grow but to keep your plants healthier. 

He told me about a study done by a company called KiS Organics in Washington about the significant, measurable increases in yields when plants get just enough water that they need and not more than that. KIS’s chief research scientist, Dr. Ben Higgins, implemented the studies and wrote the papers that are published on KIS’s website. 

The studies were undertaken at Gold Leaf Gardens, a commercial production facility in Lacey, Washington, using Blumat watering systems. Grow does not have any sort of relationship with Sustainable Village or Blumat’s; we’re simply reporting on this interesting data to best serve the growing community by giving them access to information that many people would not otherwise see. 

Higgins, who has a PhD in ecology and evolutionary biology, says they first attempted to publish their results in an open access peer-reviewed journal before deciding to simply publish the material themselves after it had been vetted by other colleagues. “We wanted as many people as possible to have this information, which is why we ended up just releasing it on our own as a white paper on our website,” Hussey says. “The journal would have been open source, but it would still have been more difficult for folks to find because once it is in a journal you basically have to go through academic channels to access it, regardless of it being open source.” 

Higgins says he has always been a proponent of divulging research even though some people in academia and in the cannabis industry want to keep their cards close to their chest. “My philosophy is a little different because sharing information that is going to benefit the plant, the consumer and everybody involved is more important than KiS Organics possibly having a slight edge in irrigation techniques,” he says. “If growers have access to best practices in sustainable and organic growing, it’s going to benefit them more.”

Using less water benefits the environment in a number of ways — less nutrients running out of soil means less algal blooms, less lost nutrients, and a more sustainable grow. Hussey says that there is some financial incentive for them to report this info because KiS Organics sells custom designs of Blumat systems and helps people set them up, which he says can be tricky the first time. “So that’s the big picture,” Hussey says. “But overall, we wanted to offer a science-based methodology because that’s one thing that separates us. We use and sell these systems, but we have this data around the design and usage that shows they really work.”

The study that Higgins and Tad Hussey, who runs the KiS business, wrote together is based on the knowledge that soil moisture plays a critical role in shaping physiological and biological responses in both plants and the microbial communities within the soil. There is a lot of knowledge about this effect in agriculture in general, but there is a lack of scientific inquiry specifically into C. sativa cultivation. 

The goal of the study was twofold: to test the hypothesis that yields would increase when C. sativa was grown in living soils with a constant soil moisture through an automated irrigation system, and that an automated irrigation system that functioned on soil water potential pressures rather than timers, would create a more stable soil environment relative to standard hand watering practices. 

In their study, 112 C. sativa plants from five distinct cultivars were grown for 73 days until harvested. The difference between the above-ground biomass (AGB) of plants grown in experimental beds which were irrigated with Blumat systems that automatically sense soil water potential were compared to control beds which were irrigated by hand. The results show that when grown in living soil with stable water pressures (irrigated with the sensors), four of five cultivars tested increased their AGB by 20-29%, with only a single cultivar decreasing (-10%) in AGB. The plants watered with the Blumats were significantly larger, averaging 24.7% more AGB than plants grown in identical medium irrigated by hand. The sensor-monitored plants yielded 5.08 pounds per eight-plant trellis while the other group yielded 3.8 pounds per eight-plant trellis. The study concludes, “To maximize the yield of numerous cultivars grown simultaneously, commercial facilities should consider utilizing automated irrigation systems that have some degree of interaction with the soil rather than relying on timers to determine when to start/stop irrigation cycles.”

Box says that growers have been hearing about this type of yield increase anecdotally for years, but truly unbiased scientific studies are rare. He says often, when a company does enter into an agreement to do this sort of study and see a significant increase in yields, they don’t reveal the results because they don’t want their competitors to enjoy a similar advantage. “They say, ‘Oh, we don’t actually want to talk about this because the results are too good and this is our industry secret now,” Box says. “But to actually do a rigorous study on it and get repeatable results, and then to publish the results is remarkable.” Let’s take a closer look.

Methods and Results

The growers grew Birthday Cake, Pineapple Mimosa, Animal Sherbert #2, Wedding Cake, and Mimosa. All plants used the same water source and were planted in the same conditions and handled the same ways throughout their growing period. Some plants were irrigated using Blumats while the others were watered by hand. The Blumat systems use Blusoak drip tape to deliver water into the soil based on moisture sensors placed within the soil. When moisture content lowers, the sensors allow water to flow through the sensor and into the drip tape and into the soil. Beds without the Blumats were watered as much or as often as deemed necessary by gardeners with no less than 10 years of cannabis growing experience. 

Mimosa actually performed better when hand-watered, but overall, the Blumat-irrigated plants were taller earlier, wth larger flower masses. Because of this increase in size, the cultivators installed trellises a week earlier than for the hand-watered plants. Both Birthday Cake and Wedding Cake increased AGB 29%. Pineapple Mimosa and Animal Sherbet #2 increased their yields by 24% and 20%, respectively. On average, Blumat systems beds yielded 24.7% more AGB relative to those that were hand watered.

Hussey says the results support what they had anecdotally heard and he wasn’t too surprised by it. “But this was the first time we had someone like Ben who could really apply more rigid methodology to our trials,” he says. “But all of our other grow trials prior to that supported these results, so it is in line with what we expected.”

Hussey is the host of a podcast called “Cannabis Cultivation and Science,” where you can find a more in-depth discussion on this exact topic with Higgins. That’s episode 51 of the podcast, which you can find in the Learn section of the KiS Organics website. To read the full study, visit this page: and visit the KiS website for information about a custom Blumat design.