Farming: vertically challenged?

With all the background noise about rising food prices and food security it's no surprise that the idea of the vertical farm is getting another airing.

It was first proposed five years ago by a team at Columbia University. As they pointed out, the practice of hauling vast amounts of food from the countryside to cities – then shifting similar amounts of organic waste back the other way – seems pretty half baked. With oil at $140 a barrel it looks doubly so.

On the vertical farm the two operations are brought together in a single, fully-integrated process right in the heart of the city. Crops would be grown hydroponically – in nutrient solution – while the farming of fish like tilapia, the grass carp, would supply animal proteins.

Crop residues would be composted and the nutrients recycled back into the growing medium, while food wastes would be fed through an anaerobic digester to produce methane for power generation and heat to speed up crop growth. For maximum efficiency human wastes – from "black-water" sewage treatment systems – would also be exploited for their nutrient supply.

The whole idea has a very futuristic appeal. Artists' impressions often show a steel-and-glass tower with crops being grown at different levels in a sort of high-rise, multi-level greenhouse. It's part of the urban landscape – a modern solution to the problems of feeding a fast-growing and increasingly urban population.

But while the principles of recycling nutrients and producing food close to consumers have real advantages at a time of rocketing energy prices, there's seems little chance of the idea actually catching on.

For a start I've yet to find a hydroponically-grown item that compares in quality to the equivalent food grown in good, old fashioned soil. Take the supermarket tomato, a prime example of an everyday staple grown in nutrient solution. In flavour and succulence it can't hold a candle to the ones I produce from grow-bags in my greenhouse.

Perhaps a more significant drawback is that – despite recent inflation – food prices are still nowhere near the levels they'd need to reach to justify shifting agriculture away from relatively cheap rural land to the high-priced real estate of the city.

The fact is, for all the hype about population explosions, there's no real shortage of food producing land on the planet. According to UN figures, the world's entire production of cereals and vegetables occupies an area of land smaller than Russia. More than twice this area is currently occupied by extensive grazing. If global commodity prices stay high it's likely that additional land will be brought under cultivation, certainly enough to make up the present food shortfall.

That said, a world supply based on a few industrially-grown, globally-traded grain crops is wasteful of scarce fossil fuels and inherently risky. There are sound strategic and economic reasons for bringing food production closer to the people who are going to eat it.

Perhaps the answer lies in greening the cities – not in a vertical direction – but on the horizontal? This is pretty much what Cuba did when the flow of Soviet oil dried up and large-scale mechanised agriculture became impossible. Under the US trade embargo the people faced starvation. The result was a proliferation of small-scale organic farms that basically kept the nation fed.

There's no reason why conurbations like London and New York shouldn't be filled with city farms in the same way as Havana. There are thousands of small areas from rooftops to urban parks that could be converted to food production. In fact it's already started to happen. Last year Harrods announced that it would be growing a range of crops – including lettuces, broad beans and tomatoes – right there on its roof.

Alternatively there's a good case for converting "green belt" land around our cities for the production of vegetables and fruit for local people. Back in the 19th century London and other cities were ringed with market gardens supplying fresh foods for the local urban population. They maintained the fertility of their soils by collecting manure from the millions of horses that were then stabled in cities.

Renewed interest in the vertical farm is a useful reminder that shorter food supply lines would bring many benefits. There's also much to be said for recycling organic nutrients including those we waste through the sewage system. But it's probably a little early to start talking up the high-rise farm.

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Farming: vertically challenged?