Revol Greens looks like a warehouse or factory from the outside. But step inside, and it's an oasis of green plunked into the frozen outdoor landscape of southern Minnesota.

The 2.5-acre greenhouse operation, the largest of its kind in the state, raises several varieties of greens in assembly-line style and began shipments to Twin Cities grocery chains last week.

It is the latest of several greenhouse ventures in recent years to test the profitability of using high-tech, energy-efficient equipment to make locally grown produce available year-round to Minnesota consumers.

"Consumers expect produce grown close to home to be fresher, tastier and better for the environment," said Revol Greens President Jay Johnson, who has been at the forefront of greenhouse growing in Minnesota for more than 20 years. "We want to meet and exceed their expectations."

Johnson in 1989 founded Bushel Boy Farms, one of the first Minnesota greenhouse operations to grow tomatoes year-round. He sold that business in 2011.

Now he and four other partners — two of them also formerly at Bushel Boy — have their sights set on greens: mostly the 4- to 5-inch baby leaf lettuce that's typically sold in bags or plastic clamshell containers as mixed greens.

The vast majority of those products are trucked from California or Arizona at this time of year, a four- to six-day journey.

"When you're looking at something that's 2,000 miles away vs. 60 miles down the road, that can get here a whole lot quicker and a whole lot fresher, it ends up being a no-brainer," said Jeremy Lee, produce director for Kowalski's Markets, which now stocks the product at its 11 stores in the greater Twin Cities area.

Other customers include Lunds & Byerlys, Coborn's and Coborn's Delivers, Jerry's Foods and some Cub Foods throughout the metro. Johnson said the company's marketing target is a 200-mile radius or four-hour drive from its operations in Medford, about 60 miles south of Minneapolis in Steele County.

Johnson said the price of Revol Greens is competitive with California brands, in part because of lower transportation costs. The company can produce 2,000 to 2,500 pounds of greens per day, he said, and is also working with St. Paul-based Bix Produce Company to distribute to local restaurants.

Inside the greenhouse, greens at various stages of growth stretch the length of two football fields, including arugula, spinach, romaine and green leaf lettuce and a striking red oak leaf variety. At first glance, the lettuce seems to be stationary. But it's growing on hundreds of white platforms — each about the size of a step-up exercise board — that float on ponds about 10 inches deep.

The setup, based on Dutch technology, is a hybrid hydroponic system that uses both soil in grooves in the boards, and nutrient-rich water circulating beneath the plants, to grow them to maturity. The floating boards with seedlings are placed at one end of the ponds, and the greens are full-grown by the time they reach the other end. Planting to harvest takes about 21 days.

"We can produce a pound of lettuce with 10 percent of the water that California outdoor farmers use in their desert climate, which in the future will be a big deal," Johnson said.

The farmland near Revol Greens receives about 36 inches of moisture per year on average, he said, and the greenhouse needs 32 inches to cover its needs, so there's no need to pump groundwater. Rain water and snow melt is collected from the building's roof, stored in a covered outdoor retention pond, and filtered, sterilized and reused repeatedly in the greenhouse's closed-loop system.

Air temperatures are controlled through a system of horizontal curtains, overhead misting and other devices.

"What we try to do is mimic March and April weather in moderate climates," said Marco de Bruin, Revol Greens' general manager and partner. The optimal temperatures for greens are warm days averaging about 70 degrees and cool nights around 55 degrees, he said. The greens also need 12 to 14 hours of sunlight, he said, which is supplemented during the short winter days with high-efficiency LED lighting.

Mary Rogers, assistant professor of horticultural science at the University of Minnesota, said Revol Greens is part of a groundswell in local greenhouse facilities that raise greens, herbs and sometimes fish. Other ventures include Urban Organics in St. Paul, Urbanize Farm in Edina and Living Greens Farm in Faribault. All are year-round operations that grow greens without pesticides or herbicides.

"It's exciting to see these businesses opening up," she said.

Rogers is not surprised that Revol Greens zeroed in on lettuce, because it's well-adapted to grow in controlled environments, has small stature with shallow roots, and has a crop turnover time of a month or less. Research, including some at the University of Minnesota, has shown that consumers cannot discern any taste difference between greens that are grown indoors hydroponically and those farmed in outdoor fields, she said, and the fresher produce grown closer to home has a much longer shelf life.

"One you harvest those leaves, you're on a time clock," Rogers said. "The freshness and the nutrient quality degrade fairly rapidly. My biggest frustration as a consumer is buying expensive organic salad mix from California and having it go bad in three or four days."

Johnson said that Revol Greens uses no pesticides or herbicides, but is not certified organic because it doesn't want to use animal byproducts for fertilizer that at some farms have been linked to E. coli, salmonella and other food safety problems. Revol Greens uses a light mineral fertilizer similar to Miracle-Gro.

Rogers said that even with fresher produce and cheaper shipping, it is tough for Minnesota greenhouses with higher energy costs and other expenses to compete with low-cost produce shipped in from California, Arizona or sometimes other countries.

"Time will tell whether these businesses can stay economically viable," she said. "There's real value in having these farms in our local community, and they're certainly selling a great product."

Tom Meersman • 612-673-7388