The passage
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In a former warehouse on the edge of a city, lettuce grows in tall stacks of trays under purple light. There is no soil and no sunlight, and the plants never see rain. This is a vertical farm, one of a growing number of indoor farms that produce food close to the people who eat it.
Instead of soil, most vertical farms grow plants with their roots in water that contains the nutrients they need. Because the water is collected and used again, these farms can use far less water than traditional fields. The lights are usually LEDs, which can be adjusted to give plants exactly the colours of light they use most. Temperature and humidity are controlled by computers, so crops can be grown all year, whatever the weather outside.
Supporters point out several benefits. Food grown inside a city travels a short distance to shops, so it can be sold fresher. Indoor crops are protected from insects, which means that pesticides are rarely needed. And because the trays are stacked, a small building can produce as much as a much larger area of farmland.
The biggest problem is energy. Plants that grow outdoors get their light for free from the sun, but an indoor farm must pay for electricity to power its lights and climate systems. For this reason, vertical farms have so far concentrated on leafy greens and herbs, which grow quickly and sell for a good price. Crops such as wheat or rice, which need a lot of space and light but are cheap to buy, are not yet worth growing indoors.
Some companies have closed after their energy bills rose. Others are trying to use renewable power or to build farms next to factories that produce waste heat. Whether vertical farming becomes a major source of food may depend on how cheap clean electricity becomes.