SELINSGROVE, Pa. — Leafy greens seemed to go on forever in the balmy heat of a newly erected greenhouse here, rows of spinach and lettuce bound for boxed salad at Pennsylvania supermarkets in coming days. Outside, on Valentine’s Day, nothing was growing.

This indoor farm, approximately 280,000 square feet, opened last month in a new industrial park, sitting on what once were soybean fields. It is the latest and largest from BrightFarms, a nationwide hydroponic greenhouse operation that aims to eliminate the long-distance trucking many greens require by growing them locally year-round.

They begin as seeds stuffed into a floating germination board, placed by hand into a tank about the size of a football field, progressing forward daily until they are ready for harvest about two weeks later. Greens grown in this Snyder County town of 5,900 already are being packed and shipped throughout the state to supermarket chains, including Giant, where they average about $3 per container.

A typical coast-to-coast shipment would take about five days. “Our stuff can be harvested and on the shelf the next day,” said general manager Tony Paar.

Mark O’Neill, of the Pennsylvania Farm Bureau, said consumers are eager for food “picked at the height of freshness," particularly if it’s grown locally. Greens from BrightFarms, about 150 miles northwest of Philadelphia, have a “Grown in Selinsgrove” label on the packaging.

Founded in 2011, BrightFarms opened its first hydroponic greenhouse in Yardley, Bucks County, in 2013, selling its greens to dozens of local supermarkets. The company has three additional hydroponic farms, and plans to build in four more states. The one in Selinsgrove, about 150 miles northwest of Philadelphia, cost $20 million.

“It takes about nine months to build one of these, and we’re still doing some construction,” said Paar. “Four acres is going to produce about two million pounds a year.”

Fast Company, a national business magazine, included BrightFarms among the “Top 10 Most Innovative Companies” in the world in 2011.

“Demand is increasing a lot faster than we can meet it,” founder Paul Lightfoot told The Inquirer in 2013. “The supermarkets want to have a consistent supply and meet the demand for local, and it’s not easy for them to do that.”

According to Vegetable Growers News, just three states — California, Florida, and Arizona — produce 76% of the country’s vegetables. Sweet corn is Pennsylvania’s top vegetable crop, followed by potatoes and snap beans. Giant, based in Carlisle, Cumberland County, said sourcing green vegetables in Pennsylvania in the winter can be tricky. The chain has been working with BrightFarms for five years.

In 2013, Lightfoot mentioned that California, the nation’s top lettuce producer along with Arizona, was experiencing a deep drought. Not much has changed out west, as snowpack in the Sierra Nevada mountains is critically low this winter.

Paar says BrightFarm uses 85% less land and 80% less water than a comparative outdoor farm to grow the vegetables, condensing the cycle with both natural and electric light. It’s never cloudy or cold in the greenhouse, meaning they can grow all year long. Carbon dioxide captured from the heating system is used to “feed” the plants.

"Right now, the sun has been almost nonexistent, " said Chris Hennessey, the farm’s head grower. “Right now, we can give them light almost 24/7, and then ease back come March and April, and then we can give them time to rest."

The greenhouse resembles a big box store from a distance, but at night, when the lights are on, BrightFarm uses the equivalent of blackout curtains to avoid light pollution.

“On a foggy night, when the fog banks off the light, it looks like aliens are coming from outer space,” Paar said. “We can make it so dark, you won’t even know it’s here.”

BrightFarm’s Selinsgrove operation has 36 employees, he said, and will likely rise to 55. Many are former employees of Wood-Mode, once Snyder County’s largest employer. The custom cabinetmaker closed abruptly last year, laying off all of its 938 workers. The company was later purchased by a local entrepreneur but only a fraction of the workforce was brought back.

“We have a lot of their people here,” Paar said. “We have a husband-and-wife team who worked there for decades.”

Paar said hydroponic greenhouses have been used in Europe for decades to grow vegetables, and in particular, flowers. On Valentine’s Day, BrightFarms’ employees were given cake and roses. They weren’t grown in Selinsgrove.