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Urban Farm BargeFarming in the city is already happening on the small scale. The Science Barge in New York City, shown here, grows tomatoes, strawberries, cucumbers and other crops in greenhouses. Energy comes from solar panels, windmills and a generator that runs on biofuels.Enrico Sacchetti

When you hear the word “farm,” chances are you picture rolling hills in the country covered with cows and cornstalks. But some scientists, engineers and city planners say the farms of the future could rise straight into the air — in skyscrapers in the world’s most populated cities.

It might sound far-fetched, but in fact, some of the technology for growing crops indoors already exists. The scientists stationed at the South Pole research station enjoy fresh salads every day from vegetables they grow in their own greenhouse. And the National Aeronautics and Space Administration, or NASA, has been experimenting for years with methods for growing fresh fruits and veggies on the moon or even on Mars.

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No soilSwiss chard grows in water enriched with nutrients in the greenhouse aboard the Science Barge. An indoor, vertical farm would probably take advantage of a similar system, re-using the water. Courtesy of www.nysunworks.org

Those in the know say bringing farming indoors solves a number of problems. First, traditional farming takes up a lot of land. In fact, it takes a plot of land as big as the entire state of Virginia just to grow enough food for all the people in New York City, says Dickson Despommier, an ecologist at Columbia University. That’s about 8 million people.

Cities that grow their own food also would become more self-reliant, and less vulnerable to catastrophes such as hurricanes that can make it impossible for trucks to deliver fresh produce to grocery stores. In addition, fruits and vegetables grown outdoors face all kinds of hazards, from flooding to insect pests to weather instability, such as late or early frosts that can damage a crop. “What happens outside is lightning bolts strike, there are floods, pests, drought,” Despommier says. “You can control everything indoors. You can't control anything outdoors.”

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Spinach on the 16th floor One idea architects and engineers have is to build this "Living Skyscraper," which would house 16 floors dedicated to farming right in the middle of the city.Blake Kurasek

To top it off, by the year 2050, the world population will grow by another 3 billion. As populations grow, the land available for farming shrinks, raising an important question: where will we grow the food for all these people? Despommier and his colleagues say “vertical farming” — growing crops in skyscrapers tens of stories high — is the answer.

Vertical farming takes up much less land than traditional, "horizontal" farming, and its advocates say it could provide new uses for hundreds of abandoned buildings in cities around the world.

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Many plants, small spaceA closeup of the Living Skyscraper proposal shows some of the different kinds of foods that could grow there. Each kind of crop, however, has its own needs in terms of light, temperature and humidity.Blake Kurasek

While vertical farms don't exist yet, their proponents say a well-designed facility could recycle water from indoor fish ponds and use that water to irrigate crops like strawberries, peppers and tomatoes. Crop waste, such as stalks and leaves, would be composted, and the gases given off from composting would be used to heat the building. Livestock such as chicken or pigs could even live in a vertical farm, their waste being recycled as a source of energy.

But those familiar with the hurdles of growing crops indoors say it's not going to be easy to make the transition to vertical farming. "If I was going to play devil's advocate, I’d say it is going to be tough," says Gene Giacomelli, who heads up the Controlled Environment Agriculture Center at the University of Arizona in Tucson.

It can be tricky to regulate climate conditions indoors, he says. Maintaining the correct balance of humidity can be especially challenging. "At the end of the day, it is going to be raining in these buildings," he says.

Plus, plants differ in their weather and lighting requirements. Tomatoes like warm, sunny weather, while greens like lettuce prefer cooler temperatures. And nearly all crop plants require lots of sunlight.

Mimicking sunlight is challenging, but scientists are learning how to make artificial lights that produce the colors, or wavelengths, of light — especially red and blue — that crop plants need. Still, artificial, electric lights present their own challenges. First, overhead lights are inefficient, giving off the majority of their energy as heat, instead of light. One type of light, called a light-emitting diode, or LED, overcomes this problem, but Giacomelli says these are still too expensive for widespread use.

That's not to say these challenges won't be overcome — but it will take time. Most experts suggest it would be anywhere between five and 15 years before the first vertical farms could be created.

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