DENVER (MainStreet) — Marijuana growers are capitalizing on Colorado’s 300 days of sunshine with a move toward establishing cultivation facilities in greenhouses, rather than indoor warehouses retrofitted to handle the colossal electrical load cannabis production requires.

And while there are significant cost savings that come from using the sun, there are significant challenges to overcome with growing weed in a greenhouse. Growers must keep the temperature and humidity in the proper range, which is largely dependent on what the environment outside the greenhouse is like.

“You may spend more on heating and cooling, depending on where the greenhouse is located,” said Matthew Sharpe, an electrical engineer with Surna, a Boulder, Colo.-based manufacturer of equipment for the legal weed industry. “But the general consensus is we need to be using the sun for cannabis. It’s just how to do that effectively and control your environment.”

Greenhouse grows use about a quarter of the lightbulbs that indoor cultivation facilities need, and at a cost of about $500 a lightbulb, that adds up, said Trent Woloveck, chief operating officer of American Cannabis Company Inc., which provides provides consulting services, manufactures cultivation products and facilities and manages a group partnership that supplies ancillary products to the marijuana industry. The cost to outfit a 100,000-square-foot building with lightbulbs is about $625,000, compared with $156,250 for the same size greenhouse.

Growing weed in greenhouses also keeps electric bills substantially lower. The electric bill for a 120,000-square-foot warehouse using 22,320 kilowatt hours is about $38,100 a month, compared to $9,525 for the same size greenhouse using 5,580 kilowatt hours.

“Greenhouses enable us to reduce carbon footprints,” Woloveck said.

Still, it’s unlikely growers would shift to greenhouses if consumers were still in search of the most attractive buds. Instead, consumers are smoking less and eating more weed — 45% of marijuana sales are now attributed to edibles.

“As more consumers are shifting toward vapor pens and edibles, the goal no longer becomes who has the best-looking flower,” said James Lowe, president of cultivation for MJardin Management, a Denver company that provides cultivation and processing services to licensed cannabis businesses nationwide. “It’s, 'How do I grow the best resin?' It’s just a different beast altogether.”

Lowe says that growers building greenhouses that try to compete with indoor facilities growing the best-looking flowers have to invest nearly as much per square foot to make that happen. A high-tech grow costs up to $100 per square foot to build, compared with about $50 a square foot for a greenhouse that grows weed purely for extraction purposes.

“But obviously, the long-term operations are substantially cheaper,” Lowe said “However, if all I’m doing is extraction, it will be designed differently.”

The trend to grow weed in greenhouses also comes as warehouse space becomes more expensive and difficult to find. Since voters approved legalizing marijuana for recreational use in 2012, growers have absorbed more than 1 million square feet of industrial space throughout 2013, according to the third-quarter industrial Market Trends report by Newmark Grubb Knight Frank. The total space occupied by the industry is more than 4 million square feet.

With the state allowing new players to enter the grow industry in October, traditional warehouse space is likely to become even scarcer, prompting further development of greenhouses for growers. Jason Thomas of Avalaon Realty Advisors, an agency that helps growers find warehouse space, estimates there is likely up to 300,000 square feet of greenhouse space in development in Pueblo and another 500,000 square feet in Denver.

"Greenhouses go up quickly, so we're looking at adding to that supply," Thomas said. "And you're able to produce monster plants compared to indoors."

--Written by Margaret Jackson for MainStreet