Why bring agriculture to cities?
Today, over half of the world’s population live in urban areas. It is predicted that, by 2050, 80% of all the food we eat will be consumed in cities!
However, people living in these areas are almost completely dependent on food brought in from rural farms. They are, therefore, vulnerable to changes in food prices and supply. Access to fresh fruit and vegetables is also often extremely limited.
Food travels thousands of miles to reach supermarket shelves, and must often be stored, processed, and packaged.
Food processing, such as canning, drying or freezing, can extend shelf life and reduce food waste. However, this uses energy, and important nutrients and vitamins can be lost or altered in the process. Growing food in cities lessens the dependence of urban populations on distant food supplies, while reducing emissions from transport, processing and packaging.
However, space in cities is often very limited. So where can these urban farms be set up?
Do we have space for urban agriculture?
Micro-gardening is one solution. This involves growing fruit, vegetables and herbs in small spaces, such as rooftops, balconies, and patios. Rooftops in particular offer large amounts of flat, sunny space on which to grow plants.
Even in limited space, micro-gardens can be very productive. For example, around 30kg of tomatoes can be produced every year from an area of 1m²!
Micro-gardens have many other environmental benefits too: they can provide habitats for birds and insects and absorb CO₂ from the air, reducing pollution.
Indeed, if all suitable roof space in Bologna, Italy, was used for urban agriculture, approximately 624 tons of CO₂ could be captured every year, and enough vegetables could be grown to feed over three-quarters of the city!
To ensure a regular water supply, gutters, pipes, and water butts can be used to channel rainwater that would otherwise have been wasted to the plants. Food waste can also be recycled and used as compost to fertilise crops.
However, not everyone has a balcony or patio, and setting up a roof garden can be expensive. While people in cities scramble for every inch of available outdoor space, large areas of indoor space are left abandoned. What if we could grow food in these areas too?
Can farms be set up indoors?
Outdoor agriculture is vulnerable to extreme weather events, which will only increase with climate change. By contrast, indoor farming systems enable ideal growing conditions, including light, temperature and nutrient supply, all year round.
Crops can be stacked in layers so more of them can be grown in a small space. This is called vertical farming. Vertical farms can be set up almost anywhere: in office buildings, underground, in shipping containers, and even in space.
Vertical farms often grow plants in water instead of soil. This system, called hydroponics, allows farmers to ensure plants receive nutrients in exactly the right amounts because nutrient levels in the water can be precisely controlled. No soil also means no weeds or other soil-based pests, reducing the need for pesticides.
Because water is recycled, hydroponic systems are incredibly water efficient. For example, lettuce grown in this way needs 13x less water to produce than lettuce grown by traditional farming methods.
However, such precise control over environmental conditions is expensive and uses a lot of energy. As clean energy sources become cheaper and more widely used, these costs will hopefully decrease.
Can we farm animals in cities?
Hydroponic systems can be combined with aquaculture in a circular system that uses fish waste to fertilise crops. This is called aquaponics. Water from the fish tank is transferred to growing plants, which remove nutrients from fish waste. The water is then recycled back to the fish tank.
Aquaponic systems imitate natural nutrient cycles, removing waste while conserving water. Because water is recirculated within a closed loop, these aquaponic systems can be set up almost anywhere, including on top of buildings.
Developments in urban agriculture are changing people’s perceptions of farming and food production as a whole. However, while they have many benefits, farming by these methods alone will not provide enough food to feed our growing population. To ensure that people have sufficient access to food, urban agriculture needs to be combined with traditional farming methods.