Salad plants are already being grown in old bomb shelters but floating dairy farms and 16-storey food towers could be next

Only the Northern line tube trains rumbling through tunnels overhead provide any clue that Growing Underground is not a standard farm.

The rows of fennel, purple radish and wasabi shoots could be in almost any polytunnel, but these plants are 100 feet below Clapham High Street and show that urban agriculture is, in some cases at least, not a fad.

The underground farm has occupied a section of the second world war air-raid shelters for nearly five years, and Richard Ballard, one of the founders, is planning to expand into the rest of the space later this year.

“The UK is the hardest market for growing salad,” he said. “We’ve got very low prices in the supermarket, so if we can make it work here we can make it work anywhere.”

The Growing Underground experience is being highlighted at two exhibitions this year: Roca London Gallery’s investigation into “agritecture”, London 2026, which opened on Saturday, and the V&A’s Food: Bigger Than the Plate in May, which will also showcase micro-farming methods such as Grocycle’s hanging mushroom bags.

Urban commercial farming – as opposed to Britain’s 330,000 allotments – is a regular topic of interest at places like the World Economic Forum in Davos, where policymakers consider whether the world’s food system, blamed for causing both obesity and malnutrition, can be fixed.

There are already plenty of urban farming projects around the world, particularly in the US, Japan and the Netherlands, ranging from aquaponics – urban fish and plant farms – to vertical farming, where plants are grown in stacked trays, a method Growing Underground also uses.

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“It’s definitely becoming an expanding industry,” Ballard said. “There’s several other businesses starting up in London in containers, smaller projects, and there are several around the country now, other vertical farms.”

Growing Underground supplies herb and salad mixes – pea shoots, garlic chives, coriander, rocket, red mustard, basil and parsley – to Marks & Spencer, Waitrose, Ocado, Whole Foods and Planet Organic, as well as restaurateurs including Michel Roux. Being in London creates an advantage, Ballard says, as they can harvest and deliver in an hour.

He reels off other advantages. Being underground means temperatures never go below 15C – surface greenhouses need to be heated. They can do more harvests: 60 crops a year, compared with about seven in a traditional farm or about 25 in a polytunnel. Electricity to power the lights is a major overhead, but the firm believes renewable energy will become cheaper.

Similar British ventures include the Jones Food Company in Lincolnshire, while in the US AeroFarms has several projects in New Jersey, and Edenworks in Brooklyn uses the nitrogen waste from the tilapia and striped bass in its aquaponic fish farm to feed its herb crop.

For Clare Brass of Department 22, a sustainability consultancy which curated the Roca London exhibition, projects like Growing Underground are vital pointers to the future.

“We are living in the most ridiculously wasteful system,” she said, citing research that shows about a third of the world’s food is lost. “We need to transition to a circular economy. Business and government are not going to do it. These are people who are innovating, and we need these people to show us the way.”

Some of the ideas presented include rooftop bee-keeping, an insect breeding farm for roundabouts in Stockholm, home food recycling in 24 hours, and a floating dairy farm in Rotterdam that is due to open later this year – a real-life interpretation of the children’s book The Cow Who Fell In the Canal.

Futuristic food tech companies may look like a great investment, but when venture capital runs out, many businesses fold. Paignton Zoo in Devon was one of the first to try vertical farming in 2009, using a system known as VertiCrop to grow leafy greens such as Swiss chard and pak choi for its monkeys. Five years later, the system was gone. The company behind it, Valcent, which later became Alterrus and set up rooftop greenhouses on carparks in Canada, went bankrupt in 2014.

“Vertical farming makes sense for microgreens,” Carolyn Steel, a London-based architect and author of Hungry City, said. Herbs are about 200 times as valuable per kilo as grains. “But why farm grain in a city when it can grow 20 miles away and spend three years in a grain store. Grain stores are one of the reasons cities emerged in the first place.”

For Steel, urban farming should be encouraged as an important reminder for city dwellers where their food comes from. “We have become very remote from our food,” she said, pointing out that London’s geography shows how it was built on its food supply. Grains came along the Thames to Bread Street, chicken entered from the east to Poultry, while beef went to Smithfield.

“Ultimately we need to pay more for food,” Steel said. “Ever since industrialisation we’ve been externalising the true cost of food, and now we’re seeing the true cost of that in terms of climate change, mass extinctions, water depletion, soil erosion and diet-related disease. Where does vertical farming sit in that?”