The Quirky Plan To Grow Fruit And Vegetables On Manchester City Centre Rooftops - Using Live Fish

The Quirky Plan To Grow Fruit And Vegetables On Manchester City Centre Rooftops - Using Live Fish

Experiments have revealed that city centre buildings could be turned into market gardens producing up to 180 million packs of salad a year

By David Thame  21 JUL 2018

Dr Andrew Jenkins and inset, the garden on the rooftop of Irwell House, Salford

Manchester’s city office blocks and apartment towers are powering a regional economy like no other. That much is obvious. But could they also be growing salads?

Experiments by a Belfast-based academic and a local property developer have revealed that city centre buildings could be turned into a market garden producing up to 180 million packs of salad a year.

Crops harvested could include lettuces, Swiss chard, chillies, courgettes and even strawberries.

The astonishing research suggests that if the walls of buildings are adapted, and roofs covered in polytunnels, individual buildings could produce tens of thousands of crops each year using soilless agriculture systems.

The high-level market gardens would rely on aquaponics – using live fish to provide nutrients to help plants grow – and hydroponics, which relies on water alone.

The high-level market gardens would rely on aquaponics – using live fish to provide proteins to help plants grow

Dr. Andrew Jenkins, now a post-doctoral research fellow at Queen's University Belfast, first worked on the idea in partnership with designers and BDP and local developer Urban Splash as far back as 2013.

The project at Irwell House, Blackfriars, Salford, demonstrated that older buildings could take the weight of rows of fish tanks, pumping and filtration systems.

They grew crops that needed more serious root systems against the windows, to give them more light, and put the heavier fishtanks on the building’s structural steel work.

The result was the potential to grow 16,000 vegetable servings a year from a single office block. The cost of the installation was just £28,000 – but a full commercial growing system would be considerably more expensive.

Dr Jenkins explains: “We extrapolated the data from Irwell House across the entire city centre’s stock of buildings – which meant designing a 3D model of the city so we could see what their surface area was, and which areas fell into shade which made them unsuitable for growing.

Crops harvested could include lettuces, Swiss chard, chillies, courgettes and even strawberries

“What we discovered is that the total surface area of the city’s big buildings is 445 hectares (1,100 acres) – of which 360 hectares (890 acres) fulfills the basic requirements for growing things.

"So there’s about 360 hectares (890 acres) of growing space within the realms of possibility, and the roof space is easier to use that the vertical wall space, because installing the tanks and coverings is more low-tech.”

However, the project has had to adapt to Manchester’s somewhat variable weather. Crop tanks on the roof need protection from wind and cold weather – meaning structures like polytunnels.

 Dr. Andrew Jenkins

Dr. Andrew Jenkins

The fish used in aquaponics also need to be hardy: at first they used quick growing Red Nile Tilapia – but native species like the common carp might be happier in the winter, and would not need heated tanks.

If there were four harvests a year Manchester could produce up to 180 million fruit and vegetable servings from its roofs and walls.

Could it really work? Dr. Jenkins says it certainly could.

"We’re having conversations about how you do the farming,” he says.

“It could be automated, which reduces cost and increases productivity – or maybe you can create jobs – or a mix of the two. But it is certainly true that people can’t be replaced in animal and plant husbandry and it could mean up to 8,400 new jobs.”

The project at Irwell House, Blackfriars, Salford

Landlords will be glad to know that if the idea catches on they will not need to make very expensive changes to their buildings. “The weight of the tanks is not carried on the floors, but on the structural steelwork,” Dr Jenkins says.

However useful market gardening on office blocks may be, Dr Jenkins cautions that it is no substitute for sorting out the U.K.’s long-term food security.

“We are hitting the hypothetical limits of agriculture in the UK, which means we are pushing our soils as hard as they can go.

"People hear of urban agriculture of the kind I’ve been investigating, and believe it could be a solution.

"If we used the external surfaces of urban buildings we could only deliver about 1.5% of the UK’s food needs. That's enough for about one million people per year, which is small in the grand scheme of things but could ultimately transform local economies and job creation in many cities in the future."

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