Connecting the Drops: Weed and Water

With the legalization of marijuana in various states and forms, conservation groups and others are asking how much legal grow operations affect water consumption. In Colorado, water managers and researchers are working together to answer that question. Maeve Conran reports as part of Connecting the Drops, our state-wide radio series on water issues.

Tim Cullen is CEO of the Colorado Harvest Company, one of the state’s largest marijuana businesses. It employs more than 75 people at their 3 retail outlets in Denver and their 10,000 square foot grow facility which houses roughly 3,000 plants.

Here in the nursery room, Cullen points to a row of young plants that he calls “cloners”. In about 5 months these plants will mature with golf ball sized flower buds that retail for up to $300 an ounce. Plants here are grown in coco fiber rather than soil, a substance with no nutrient value. Cullen says that allows them to closely monitor all the nutrients going to the plant, all delivered through water. “We never let water run out of these plants and if you look into these trays, they’re designed to hold water in them …we don’t want any water to run out of the bottoms of the plants cos that’s just wasted nutrient.”

Practically every drop of water is accounted for in this grow facility, a practice that Jeff Tejral, Manager of Conservation for Denver Water has observed in other operations.

“I’ve been in a lot of commercial and industrial sites for audits and I’ve never seen a place that’s actually written down how much water has been used in an area before…that was new to me, that was a best practice I’d like to see a lot of people using.”

In the early days of legal marijuana cultivation in Colorado, Tejral and other water managers started to pay attention to how much water was being used. “We also saw the articles coming out…Mother Jones: 6 gallons per plant per day…that piqued our interest.”

Jeff Tejral says he’s been impressed with the attitudes towards water that he’s seen in Denver marijuana grow facilities. “I’ve been in a lot of commercial and industrial sites for audits and I’ve never seen a place that’s actually written down how much water has been used in an area before…that was new to me, that was a best practice I’d like to see a lot of people using.”

In 2014, California Fish and Wildlife Officials started clamping down on illegal marijuana operations which they said were using 6 to 8 gallons of water per plant per day, stressing drought stricken water-sheds. But in Denver, Tejral says he did not see growers using anywhere near that amount. “That was way more than what I ever saw, I would have really noticed that in some of these grow operations with several thousand plants.”

However, due to the nascent nature of the industry, and the ongoing federal prohibition of marijuana, little official research has been done into exactly how much water cannabis plants use. That limits options for shared best practices across the industry. James Zazanis is President of ZJ analytics LLC, an agricultural research company in Maryland. He is partnering with another marijuana grow facility in Denver to monitor water use, with a goal of creating guidelines for the industry. Using soil moisture sensors they monitor in real time how much water the plants are using. While no results are available yet, Zazanis says what he’s seen at different grow facilities in Denver is encouraging.

“These guys are the leaders in using the newest technology, they want to understand how plants work on a scientific level and they’re really championing conservation.”

Back at Colorado Harvest Company, Tim Cullen says he too is eager to see research into conservation techniques. “When you’re talking about the number of plants we’re dealing with, this isn’t like filling a pitcher up at your sink and watering your houseplants. Our nutrient bills are close to $10,000-$12,000 a month so we’re not wasting that water once it has nutrient in it, it really needs to stay in the plant.”

As the marijuana industry continues to grow and evolve, Denver Water says they’ll be looking to Zazanis’ findings to help inform them of best practices.

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