Grow-lamp-loving, water-sucking marijuana plants aren’t so green

Pot’s energy, water use is under scrutiny

Marijuana’s reputation is about as green as they come. Not only is it an oxygen-producing and carbon-dioxide-absorbing plant, its alternative-medicine bona fides and hippie ethos are often associated with the environmental movement.

Yet cannabis plants suck up around twice as much water as maize, soybeans, wheat and wine grapes, according to a 2021 study in the Journal of Cannabis Research. Additionally, growing indoors requires extensive lighting and climate control, making it particularly energy intensive. Morningstar estimates that cannabis cultivation will account for 1% of total U.S. electricity demand by 2030.

It’s a problem that the industry is trying to address — but cultivators have a long way to go, according to my interviews in the run-up to last week’s industry meeting, called Regenerative Cannabis Live, at the United Nations. Marijuana’s federal illegality means there hasn’t been much research into its environmental footprint. 

“People are looking at cannabis as if it’s just up the ladder from crypto mining in terms of sustainability,” said Chris Hagedorn, executive vice president of Scotts Miracle-Gro and division president of Hawthorne Gardening Co., a subsidiary that provides lighting, nutrients and other materials for indoor and hydroponic growing. Mining for cryptocurrencies such as bitcoin, which requires vast computing power, is famously harmful to the environment. 

For the nascent cannabis industry’s small, young companies, the initial challenge of getting up and running has largely outweighed questions about environmental impact, but that’s beginning to change, Hagedorn said. Since Hawthorne started offering more energy-efficient LED lights to customers in 2019, they’ve quickly become 70% of the company’s lighting sales, he told me.

Hawthorne is trying to cater to environmentally conscious cultivators by offering new growing mediums to replace items such as “stone wool,” made from volcanic rock that isn’t recyclable. Hawthorne sells CocoPro, made from coconut fibers, and announced last week the acquisition of Cyco, an Australia-based growing-media company. It also has a filtration system that reduces water waste, Hydro-Logic.

Much of the industry’s environmental challenge stems from the plant itself: Not only does the sun-loving plant require more light than many crops, it’s also extremely sensitive to humidity in the last weeks of flowering. This can can foster mold and requires energy-intensive dehumidification systems.

There’s also a legal element. Because cannabis can’t be shipped across national and state borders, it can’t be imported to cold climates like most agricultural products. This makes indoor cultivation a necessity in many places. And even if laws change, cultivators of high-end marijuana prefer the control of indoor climates, which allows them to create marijuana with different concentrations of secondary compounds and flavor profiles, which can increase the value of raw flower or help create products based on extracts.

There may be a happy medium in a shift to greenhouses, which take advantage of free sunlight while also allowing for some environmental control, said Ryan Douglas, a Miami-based cannabis growth consultant.

Douglas, who spoke at the conference last week, said that many entrepreneurs don’t stop to consider the economic and environmental benefits of greenhouses in their race to set up cultivation sites. Products such as blackout panels can be used to help stimulate flowering, while innovations like semitransparent solar panels can help provide some shade where needed.

The savings can be huge: Greenhouses or hybrid growing sites require 134 kilowatt hours per square foot, versus 262 for indoor cultivation, according to a 2018 report from New Frontier Data. 

“The majority of new cultivation sites are still indoors,” Douglas said.

“But indoors you reach a ceiling on price savings; we can’t make the plant need less LED light, or need less HVAC.”