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In Centennial, there are plans afoot to launch what would be Colorado’s largest rooftop greenhouse — a 2-acre operation on top of a to-be-built sports complex that will grow and package nearly 2 tons of leafy greens a day from a perch three stories above Interstate 25.

It’s a novel enough concept that elected leaders in the south suburb first need to change their zoning to allow an agricultural use currently not permitted in the 36acre mixed-use project known as The District, which is beginning to sprout just north of the Ikea store on the west side of I-25.

The City Council is expected to vote on the zoning change next month.

“The concept of produce being grown to provide for restaurants and residents nearby is innovative, and it’s in keeping with Centennial’s reputation for being forward-looking and futureready,” Councilman Mike Sutherland said. “Space in a metropolitan area is expensive, and ideas that utilize maximum use of available space will be both aesthetically and economically pleasing.”

Growing and harvesting food atop buildings is not a new phenomenon in the metro area — Altius Farms’ 7,000-square-foot greenhouse atop sushi restaurant Uchi in downtown Denver has gotten some attention in recent years, with the operation yielding leafy greens, herbs and edible flowers like Genovese basil and red Russian kale.

But most efforts to harvest from urban rooftops have been on a much smaller scale than what is proposed in Centennial, which will boast a 90,000-square-foot greenhouse and will operate 16 hours a day. It is expected to produce 3,800 pounds of leafy greens a day.

“I think it’s a direction we’re headed in and a chance to further develop urban horticulture and see where it can go,” said Joshua Craver, a Colorado State University professor who specializes in controlled environment horticulture and has been involved in the creation of a rooftop garden and greenhouse at the school’s Spur complex at the National Western Center. “Any time these operations show up, it’s exciting.”

The greenhouse in Centennial isn’t expected to grow its first head of lettuce for another few years as the project works its way through the city’s approvals process and goes under construction. But when complete, Blaine Longnecker said, it will set an example for the rest of the region.

“When you have large buildings like this, it seems like a better use of that space to do this,” said Longnecker, managing principal of Sphere Sports Management. “Let’s be on the leading edge here.”

Denver-based Sphere Sports Management is the entity behind a proposed nine-story hotel and attached sports complex — complete with indoor ice rinks, turf fields, a pool and basketball courts — in The District. The greenhouse would sit atop the sports complex.

The idea of using the building’s roof for anything other than conventional heating and cooling equipment wasn’t immediately apparent, Longnecker said.

“At first, it was kind of a joke,” he said. “Hey, we can grow tomatoes up there.”

But when he became aware of the financial potential of leafy greens. Longnecker penciled out the project’s feasibility and was pleased to discover that although it will cost him about $30 million to get the greenhouse up and running, he should be able to generate about $6 million annually selling the romaine, red leaf and green leaf lettuce that will be harvested.

“Leafy green lettuce — that’s a cash crop,” he said. “We’ll be selling wholesale to King Soopers, Safeway, Whole Foods, Trader Joe’s and to restaurants.”

The greenhouse will use assembly-line technology from Finnish company Green Automation to plant, grow and harvest the lettuce without soil, minimizing human contact with the produce and allowing the operation to run lean, with about a dozen employees on hand. A system of troughs holding the lettuce will continuously move and adjust as the plants grow.

The lettuce will be packaged on the roof and lowered to loading docks on street level via a freight elevator.

“This is a fully automated hydroponic growing system that is extremely water-conscious,” said Marc Plinke, founder and chief operating officer of Boulder-based Ceres Greenhouse Solutions.

Plinke, whose company will design the greenhouse for Sphere Sports Management, said one of the immediate benefits of the project will be the cooling effect a greenhouse full of plants — as opposed to an empty expansive, reflective flat roof — will have on surrounding buildings.

“Instead of heating up the city, you’re using the sun’s energy to grow food,” he said. “We’re seeing an uptick in people’s interest in our cities becoming greener and cooler.”

The urban “heat island” effect from sun-blasted roofs was the main driver that propelled Denver’s green roofs initiative forward, a measure voters passed nearly five years ago. A study of surface and air temperatures in 108 cities, including Denver, found that radiation of heat from asphalt landscapes boosts the temperature by up to 20 degrees.

Growing produce on a Centennial rooftop also gives a boost to the local food, farm-to-table movement, which encourages people to eat food that is grown closer to where they live.

“That lettuce, being that it’s so fresh, has a longer shelf life,” Longnecker said.

The trajectory for more indoor agriculture in metro Denver is on the upswing, even if it isn’t always rooftop-based. Gotham Greens, one of the bigger players in the space, was founded a decade ago in Brooklyn, N.Y. By next year, CEO Viraj Puri said, the company will own and operate 13 high-tech, climate-controlled hydroponic greenhouses, totaling more than 40 acres across nine states.

That include s a 30,000-square-foot greenhouse behind Stanley Marketplace in Aurora that opened in 2020. A second Gotham Greens facility is scheduled to open in Windsor in 2023.

We see a bright future ahead for different forms of controlled environment agriculture, whether at ground level or on rooftops of buildings,” Puri said. “We believe they will take different shapes and forms and be located in different areas, but the need for more resourceefficient indoor farming is clear, and we expect the industry to proliferate.”

This year, Florida based Kalera opened a 90,000-square-foot warehouse in Aurora to house a vertical farming operation, where eventually 15 million heads of lettuce are expected to be produced per year. The vertical farming industry is forecast to grow globally from $3.1 billion last year to $9.7 billion by 2026, according to the data analysis company ResearchandMarkets.com.

As far as indoor or urban rooftop agriculture posing a threat to Colorado’s $47 billion annual field grown haul, with its nearly 200,000 jobs, CSU’s Craver said it is minimal. It’s likely urban farming initiatives, while on a tear, will remain supplementary to the larger industry, he said.

“There’s a role a controlled environment can play, but it’s not a one-to one replacement for conventional agriculture,” Craver said.

A developer is proposing a 2-acre rooftop greenhouse on a to-be-built sports complex in Centennial — a 16-hour-a-day operation that will yield nearly 2 tons of leafy greens daily.