F ROM THE outside it looks like a tall, metal-clad barn. But step in, through a large airlock designed to keep out the bugs, and a kaleidoscopic scene emerges. A central aisle is flanked by two pairs of towers. Each tower is stacked with a dozen or so trays on which are growing strawberries, kale, red lettuce and coriander. And each tray is bathed in vibrant light of different colours, mostly hues of blue and magenta. Douglas Elder, who is in charge of this artificial Eden, taps some instructions into an app on his mobile phone and, with a short whirr of machinery, a tray of lush, green basil slides out for his inspection.

Mr Elder is product manager for Intelligent Growth Solutions ( IGS ), a “vertical farming” company based at Invergowrie, near Dundee, in Scotland. Each of the nine-metre-high towers in the demonstration unit that he runs occupies barely 40 square metres. But by stacking the trays one on top of another an individual tower provides up to 350 square metres of growing area. Using his phone again, Mr Elder changes the colours and brightness of the 1,000 light-emitting diodes ( LED s) strung out above each tray. The app can also control the temperature, humidity and ventilation, and the hydroponic system that supplies the plants, growing on various non-soil substrates, with water and nutrients. Armed with his trusty phone, Mr Elder says he can run the farm almost single-handedly.

Plant power

Vertical farming of this sort is not, of itself, a new idea. The term goes back to 1915, though it took a century for the first commercial vertical farms to be built. But the business is now taking off. SoftBank, a Japanese firm, Google’s former boss Eric Schmidt and Amazon’s founder Jeff Bezos have between them ploughed more than $200m into Plenty, a vertical-farming company based in San Francisco. And in June Ocado, a British online grocery, splashed out £17m ($21.3m) on vertical-farming businesses to grow fresh produce within its automated distribution depots.

The interest of investors is growing just as technology promises to turn vertical-farming operations into efficient “plant factories”. The high-tech LED s in IGS ’s demonstration unit are optimised so that nary a photon is wasted. The hydroponics, and the recycling that supports them, mean the only water lost from the system is that which ends up as part of one of the plants themselves. And towers mean the system is modular, and so can be scaled up. Most of the systems which IGS hopes to start delivering to customers early next year will consist of ten or more towers.

Some people, however, remain sceptical about how much vertical farms have to offer that good-old-fashioned greenhouses do not. Vertical farms are certainly more compact—a bonus in places like cities where land is expensive. Since sales of fresh produce to the urban masses are often touted as one of vertical farming’s biggest opportunities, that is important. But a greenhouse gets its light, and much of its heat, free, courtesy of the sun. And modern greenhouses can also use solar-powered supplementary LED lighting to extend their growing seasons and hydroponic systems to save water, says Viraj Puri, co-founder of Gotham Greens, an urban-farming company that operates greenhouses on the roofs of buildings in New York and Chicago. As for food miles, they could not get any shorter for Gotham Greens’s rooftop greenhouse in Brooklyn, which supplies the Whole Foods Market located downstairs.

The biggest drawback of vertical farming is the high cost of the electricity required to run the large number of LEDS . This has meant that production has been commercially viable for high-value, perishable produce only, such as salad leaves and herbs. That, nevertheless, is a market not to be sniffed at. But for a broader range of produce, it can prove too expensive. In 2014 Louis Albright, an emeritus professor of biological and environmental engineering at Cornell University in America, calculated that a loaf of bread made from wheat grown in a vertical farm would be priced at about $23.

Blue is the colour

One way of saving electricity is to use LED s that generate only the colours that plants require, instead of the full spectrum of plain white light. Plants are green because their leaves contain chlorophyll, a pigment that reflects the green light in the middle of the spectrum while absorbing and using for photosynthesis the blue and red wavelengths at either end of it.

The vertical farm at Invergowrie takes this idea further. It uses LED s that are highly tuneable. Although the lights produce mostly blue and red wavelengths, researchers now know that other colours play an important role at various stages of a plant’s development, says David Farquhar, IGS ’s chief executive. A dose of green at an appropriate moment produces a higher yield. A timely spot of infrared can improve the quality of foliage. The lights can also produce various blue/red mixes.

To operate these LED s efficiently, the company has developed a low-voltage power-distribution system. This, says Mr Farquhar, can cut energy costs to about half of those incurred by existing vertical farms. As a result, all four towers can produce 15-25 tonnes a year of herbs, salad leaves, fruit and vegetables. This, the company claims, is between two and three times more than a conventional greenhouse with an equivalent but horizontal growing area, and equipped with supplementary lighting and heating, could manage. And the system can grow all this produce at a similar cost-per-kilogram.

One of the jobs of the Invergowrie unit is to develop lighting regimes tailored to individual crops. Another is to develop algorithms to control, in an equally bespoke way, the climatic conditions preferred by different crops. The idea is to design crop-specific weather “recipes” in order to boost the yield and quality of whatever varieties are grown in the vertical farm. All the processes involved are engineered to be efficient. Irrigation, for instance, relies on captured rainwater. This is cleaned and recycled, but only 5% gets used up by each harvest—and most of that as the water-content in the plants themselves. Ventilation is also a closed loop, harvesting surplus heat from the LED s while managing humidity and oxygen levels.

By reducing running costs, the system should make it profitable to grow a wider variety of produce vertically. The firm has already succeeded with some root vegetables, such as radishes and baby turnips. Bulk field crops, such as wheat and rice, may never make sense for a vertical farm, and larger, heavier vegetables would be tricky to raise. This means full-grown potatoes are probably off the menu, at least with existing technology.

Seed potatoes, though, are a good candidate, says Colin Campbell, head of the James Hutton Institute, a plant-science research centre backed by the Scottish government. It is based next door to IGS and works with the company. Many fields around the world, Dr Campbell observes, are suffering a growing burden of pests and disease, such as potato-cyst nematode. In the controlled environment of a vertical farm, from which both pests and diseases can be excluded, seed potatoes could be propagated more efficiently than in the big, bad outdoor world. This would give them a head start when they were planted out in fields.

The institute’s researchers are also looking at plant varieties that might do particularly well indoors, including old varieties passed over in the search for crops which can withstand the rigours of intensive farming systems. By dipping into the institute’s gene banks, Dr Campbell thinks it may find some long-forgotten fruits and vegetables that would thrive in the security of a vertical farm.

All this could go down well with foodies, and unlock new and forgotten flavours. Shoppers might even find some exotic varieties growing in supermarket aisles. In Berlin a company called Infarm provides remotely controlled shelved growing cabinets for shops, warehouses and restaurants. Herbs and salad leaves, including exotics such as Genovese basil and Peruvian mint, are resupplied with seedlings from the company’s nursery as the mature plants are picked.