Farming on the rooftops
On the roofs of warehouses, schools and apartment blocks, a quiet change is taking place. Spaces that were once covered with gravel and air-conditioning units are being turned into productive gardens. Supporters of rooftop farming argue that it could bring fresh food closer to the people who eat it, while critics question whether such projects can ever grow more than a symbolic amount.
The idea is not entirely new. In the early twentieth century, some hotels in large cities kept small vegetable plots on their roofs to supply their kitchens. However, these gardens were usually treated as a luxury rather than a serious source of food. What has changed in recent decades is the technology available. Lightweight growing materials, which weigh far less than ordinary soil, mean that many roofs can now carry planting beds without expensive structural work.
One of the strongest arguments for rooftop farms concerns transport. Much of the fruit and vegetables sold in cities travels hundreds of kilometres before reaching a shop. Lettuce grown on a supermarket roof, by contrast, can be harvested in the morning and sold the same afternoon. This not only reduces fuel use but also means that produce can be picked when it is ripe instead of while it is still green.
Rooftop gardens may also help the buildings themselves. A layer of plants and soil acts as insulation, keeping the rooms below cooler in summer. One study of an office building found that the top floor needed noticeably less air-conditioning after a garden was installed. In heavy rain, the plants absorb water that would otherwise run straight into overloaded drains, although the amount depends greatly on the depth of the growing material.
Nevertheless, the challenges are considerable. Roofs are exposed to strong winds and intense sunlight, so crops often need more water than they would at ground level. Getting tools, seeds and workers up to the roof can be difficult, particularly in older buildings without lifts. In addition, the cost of setting up a farm is high, and many projects depend on grants from local governments. When this money ends, some farms are forced to close.
For these reasons, most experts do not expect rooftop farms to feed entire cities. Instead, they see them as one part of a wider system. Their greatest value may lie in education: school gardens, for example, allow children to see how food is produced and encourage them to eat more vegetables. In this sense, a roof full of tomatoes may change attitudes even if it does little to change the food supply.
