In the U.S., one square foot of indoor marijuana cultivation uses four times more energy than the same space in a hospital, eight times more energy than a commercial building, and 20 times more energy than a center for religious worship, according to a study by Lewis and Clark College.

But a rising number of people in the fast-growing cannabis industry are trying to reduce their environmental footprint, from energy to water to pesticides. Still, a lack of research and regulation has left an industry that is on track to post $20.2 billion in sales by 2021 in a tough position.

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