Farming upwards: the promise of vertical agriculture

AImagine a farm with no fields, no tractors and no weather. Inside a windowless building on the edge of a city, lettuces, herbs and strawberries grow on shelves stacked from floor to ceiling, their roots bathed in nutrient-rich water rather than soil. Instead of sunlight, they receive light from rows of LED lamps, tuned to the particular colours that plants use most efficiently for photosynthesis. Temperature, humidity and even the level of carbon dioxide in the air are controlled by computer, and visitors are usually required to wear protective clothing so that they do not carry insects or diseases in from outside. This is vertical farming, and over the past fifteen years it has grown from an experimental idea into a commercial industry, with large indoor farms now operating in North America, Europe and Asia.

BThe idea itself is not new. Growing plants without soil, a technique known as hydroponics, has been studied since the nineteenth century, and greenhouses have long been used to extend growing seasons. The concept of farming inside tall buildings was popularised in the early 2000s by academics who imagined entire skyscrapers devoted to food production. What made modern vertical farms possible, however, was a dramatic fall in the price of LED lighting, combined with improvements in sensors and software. LEDs produce far less heat than older types of lamp, which means they can be placed close to the plants, allowing many layers to be stacked in a single room.

CSupporters point to several advantages. Because conditions are controlled, crops can be grown all year round, regardless of droughts, floods or frost. Most vertical farms use far less water than conventional agriculture, since water that is not absorbed by the plants is collected and recycled rather than lost to the ground. Pests are rare inside a sealed building, so chemical pesticides are seldom needed. And because farms can be built close to the cities they supply, produce can reach shops within hours of being harvested, reducing transport costs and food waste. Some supporters go further, arguing that because vertical farms occupy so little land, they could allow farmland elsewhere to be returned to forest or other natural habitats.

DEnergy, however, is the industry's greatest weakness. Sunlight is free; electric light is not. Lighting, heating and cooling a vertical farm requires large amounts of electricity, and in places where that electricity comes mainly from fossil fuels, the carbon footprint of a lettuce grown indoors can be higher than that of one grown in a field and transported a long distance. Rising energy prices in recent years have pushed a number of well-funded companies into financial difficulty, and several have closed altogether. Some operators have responded by installing solar panels or by building their farms where renewable electricity is cheap, but such solutions are not available everywhere. Critics argue that the industry was promoted too enthusiastically before its economics had been properly tested.

EThere are also limits to what can be grown. At present, vertical farms concentrate on leafy greens, herbs and a few fruits such as strawberries. These crops grow quickly, are small enough to fit on narrow shelves and can be sold at relatively high prices. Staple crops such as wheat, rice and maize are a different matter. They take months to mature, need a great deal of space and are sold cheaply, so growing them indoors would cost far more than the crop is worth. For the foreseeable future, therefore, vertical farms are unlikely to replace conventional agriculture; at most, they will supplement it.

FNevertheless, some researchers believe that the technology has an important role to play in particular places. In desert regions, where water is scarce and summer temperatures are too high for many crops, indoor farms can produce fresh vegetables that would otherwise have to be imported. In cold, remote communities in the far north, for example, they can supply fresh food during long winters when nothing grows outside. Plant scientists are also using indoor growing rooms to breed new varieties more quickly, since several generations can be raised in a single year. In these specialised settings, the high cost of energy may be a price worth paying.