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. (Learn about the science of weed.)

In National Geographic magazine’s June 2015 edition, Editor-In-Chief Susan Goldberg wrote about the