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The U.S. enjoys robust, year-round produce from warm-weather states, so greenhouses aren't a huge part of the winter growing season. However, they are gaining a popularity in many parts of the country. NPR's Dan Charles reports.
DAN CHARLES, BYLINE: It's a gray, chilly, fall day in eastern Pennsylvania. But I step inside a building with walls and ceilings made of glass and feel the warmth of trapped sunlight. In front of me I see a sea of green, more than an acre of baby salad greens.
PAUL LIGHTFOOT: It looks like a field of lettuce. It's actually a field of boards with lettuce growing on them.
CHARLES: This is Paul Lightfoot, CEO of the company BrightFarms, which built this greenhouse. He shows me how the plants and the boards are all floating on ponds of water. He lifts up one of the boards.
LIGHTFOOT: And now you can see the roots - the roots hanging down below the board. These look like beautiful, nice, healthy roots and they're obviously soaking up the nutrients from the water.
CHARLES: They're fed a precisely balanced diet of nutrients through the water. They get energy from the sun and, this time of year, also some lights overhead. They go into the pond as pale seedlings, so tiny you can hardly see them.
LIGHTFOOT: See the little fuzzy guys.
CHARLES: Those are going to turn into green plants?
LIGHTFOOT: Yeah, in fact, just keep looking. That's what happens day by day by day by day.
CHARLES: Thirteen days from now, this will be baby kale, ready for harvest. They grow fast because they are pampered, with perfect temperatures, optimal light. In fact, 10 or 20 times more lettuce will come out of this greenhouse in a year per acre than from an outdoor field. Some countries grow a lot of their vegetables in greenhouses. In the Netherlands or Canada you can find vegetable greenhouses that cover a hundred acres, but rarely in the United States. There's a simple reason. Growing vegetables in the open air fields of California and Arizona is cheaper. But Paul Lightfoot is betting that some of these vegetables, starting with salad greens and fresh tomatoes, will be moving indoors soon. And to show me why, he drives me to a supermarket nearby. It's selling his products.
LIGHTFOOT: Baby arugula, baby spinach, kale blend - and we can see by looking at it that this has got about nine days left on it.
CHARLES: Nine days until the expiration date. These plants came from his greenhouse just a few days ago. Printed on the packages in big letters - locally grown. Right next to them is the competition - organic salad greens from Arizona or California. Same price, but some of that arugula and spinach looks a little wilted after the long trip across the country. And that is part one of Paul Lightfoot's sales pitch.
LIGHTFOOT: I mean, you can see the difference in freshness, so it's going to taste better. It's going to last longer in a refrigerator.
CHARLES: The second part of Lightfoot's pitch for local greenhouses in environmental. Those fields in Arizona and California are in deserts, he says. The water they need is increasingly scarce and costly.
LIGHTFOOT: In the United States, we just realized that we didn't have endless land and water a few weeks ago almost.
CHARLES: Now, outside experts say the case for greenhouses is not always quite so convincing. They do take less water, but greenhouses in cool, dark places need extra heat and light, which usually comes from burning coal or gas, adding to that global greenhouse effect. Neil Mattson, a greenhouse expert at Cornell University, says growing lettuce in greenhouses in New York state can release twice as much climate-warming gases as growing lettuce in California, even when you consider the fuel burned to ship it across the country.
NEIL MATTSON: It's not so good, and that's the status quo.
CHARLES: But he also says that could improve with better lighting and heating systems. Growing in greenhouses is also a little more expensive usually, and it's a lot more expensive if you try to do it in cities or entirely with artificial light. But the big advantage, Mattson says, is the freshness. And that's why the number of vegetable acres under glass in the United States is rising.
MATTSON: I think it really has legs, and ultimately it's going to depend on how robust consumer demand is for fresh, local food.
CHARLES: According to Paul Lightfoot from BrightFarms, it's plenty robust.
LIGHTFOOT: The demand is way higher for this product than our capacity is right now. There's no limit right now. We're raising the capital. We're building two other greenhouses that are much bigger than this.
CHARLES: Those greenhouses are outside Washington, D.C. and Chicago. The one near Chicago will take advantage of waste heat from a nearby ethanol plant - another advantage. Right now, they're growing salad greens and tomatoes. Down the road, he says, it could be any vegetable that tastes better if you don't have to ship it across the country. Dan Charles, NPR News.
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