URBAN warehouses, derelict buildings and high-rises are the last places you’d expect to find the seeds of a green revolution. But from Singapore to Scranton, Pennsylvania, “vertical farms” are promising a new, environmentally friendly way to feed the rapidly swelling populations of cities worldwide.

In March, the world’s largest vertical farm is set to open up shop in Scranton. Built by Green Spirit Farms (GSF) of New Buffalo, Michigan, it will only be a single storey covering 3.25 hectares, but with racks stacked six high it will house 17 million plants. And it is just one of a growing number.

Vertical farms aim to avoid the problems inherent in growing food crops in drought-and-disease-prone fields many hundreds of kilometres from the population centres in which they will be consumed. Instead, Dickson Despommier – an ecologist at Columbia University in New York City who has championed vertical farms since 1999 – suggests that food should be grown year-round in high-rise urban buildings, reducing the need for the carbon-emitting transport of fruit and vegetables

The plant racks in a vertical farm can be fed nutrients by water-conserving, soil-free hydroponic systems and lit by LEDs that mimic sunlight. And they need not be difficult to manage: control software can choreograph rotating racks of plants so each gets the same amount of light, and direct water pumps to ensure nutrients are evenly distributed.

The whole apparatus can be monitored from a farmer’s smartphone, says GSF’s R&D manager, Daniel Kluko. He says the new farm in Scranton will grow 14 lettuce crops per year, as well as spinach, kale, tomatoes, peppers, basil and strawberries. Its output will be almost 10 times greater than the firm’s first vertical farm, which opened in New Buffalo in 2011.

Proponents see vertical farming as a way to feed a global population that is urbanising fast: 86 per cent of the people in the developed world will live in cities by 2050, the United Nations predicts. It could make food supplies more secure as well, because production can continue even when extreme weather strikes. And as long as farmers are careful to protect their indoor “fields” from pests, vertical farming needs no herbicides or insecticides. They also conserve water far better than earthbound farming.

GSF’s first farm was inspired by the long-term drought that has been afflicting many parts of the US. “Water is a big issue,” says Kluko. “We have designed our vertical farms to recycle it, and they use 98 per cent less water per item of produce than traditional farming.” That’s done in part by scavenging water from the grow room’s atmosphere with a dehumidifier. It’s a machine with a dual role, as excess humidity can lead to problems like leaf mould.

Most vertical farms rely on natural light as much as possible. In sunny, near-equatorial Singapore, entrepreneur Jack Ng’s SkyGreens vertical farm needs no artificial lighting to promote growth. Instead, his four-storey glass-sided farm contains mobile racks of Chinese cabbage and lettuce that rotate slowly up to the sunnier heights of the building on a low-power elevator.

Conversely, in Japan, Kyoto-based Nuvege (pronounced “new veggie”) runs a windowless indoor farm. In a cavernous facility reminiscent of an aircraft hangar, Nuvege’s LED lighting is tuned to two types of chlorophyll, one preferring red light and the other blue. “Tuned to these spectra, you can grow a plant no matter where it is,” Despommier notes. Indeed, Nuvege produces 6 million lettuces a year in this way, for customers including Subway and Disneyland Tokyo.

In such arrangements, the electricity bills can add up quickly. Today’s LEDs are only about 28 per cent efficient, which keeps the cost of produce high and prevents vertical farms from competing in regions where cheap vegetables are abundant. However, lighting engineers at Philips in the Netherlands have demonstrated LEDs with 68 per cent efficiency, which could dramatically cut costs.

And the latest research shows that plants do not need always-on artificial sunlight, Despommier says: they can experience light that varies in intensity through the day – moving from an artificial dawn through to noon and dusk. Mimicking these changes will save energy too. Such tricks already play a small part at GSF: infrared LEDs mimic 5 minutes of a fading sunset at the end of each day. “It puts peppers and tomatoes into their flowering period quicker,” says Kluko.

Advances in vertical farms could trickle through from other sources, too. The US Defense Advanced Research Projects Agency is using an 18-storey vertical farm in College Station, Texas, to produce genetically modified plants that make proteins useful in vaccines. Adversity also plays its part: the tsunami-sparked nuclear accident in Fukushima, Japan, in 2011 is leading to innovation in vertical farming because much of the region’s irradiated farmland can no longer be used.

“Fukushima has had a riveting effect on this field,” says Despommier. “People were taking their food to the Geiger counter before the checkout counter.”