Researchers with the Institute for Sustainable Food at the University of Sheffield in the UK used their hometown as a case study to examine the potential for expanding food production in cities.

The researchers mapped the “green infrastructure” — parks, gardens, roadside verges, and woodland areas — and “grey infrastructure” such as buildings across the city of Sheffield and determined that, if gardens covered just 10 percent of the city’s green spaces, those gardens could provide 15 percent of the local population with their “five a day,” the recommended five daily portions of fruits and vegetables.

Altogether, the researchers calculated that there are about 98 square meters per Sheffield resident that could be opened up to soil-based horticulture: 71 square meters in domestic gardens and allotments and 27 square meters in other green infrastructure. If all of this green space was used to grow food, it could supply approximately 709,000 people — or 122% of the population of Sheffield — with their “five a day.”

Urban horticulture has vast untapped potential, a new study has found.

Researchers with the Institute for Sustainable Food at the University of Sheffield in the UK used their hometown as a case study to examine the potential for expanding food production in cities. They mapped the “green infrastructure” — parks, gardens, roadside verges, and woodland areas — and “grey infrastructure” such as buildings across the city of Sheffield using high-spatial-resolution datasets from Ordnance Survey and Google Earth. That allowed them to determine that, if gardens covered just 10 percent of the city’s green spaces, those gardens could provide 15 percent of the local population with their “five a day,” the recommended five daily portions of fruits and vegetables.

The “five a day” guideline is based on the World Health Organization’s recommendation that individuals eat “a minimum of 400g of fruit and vegetables per day (excluding potatoes and other starchy tubers) for the prevention of chronic diseases such as heart disease, cancer, diabetes and obesity, as well as for the prevention and alleviation of several micronutrient deficiencies, especially in less developed countries.”

According to Jill Edmondson, an environmental scientist at the University of Sheffield and lead author of the study detailing the team’s findings published in the journal Nature Food last week, urban gardens are not just a means of providing nutritious food to city dwellers, but also a way of improving food security. Just 16% of fruits and 53% of vegetables consumed in the UK are grown domestically.

“At the moment, the UK is utterly dependent on complex international supply chains for the vast majority of our fruit and half of our veg – but our research suggests there is more than enough space to grow what we need on our doorsteps,” Edmondson said in a statement. “Even farming a small percentage of available land could transform the health of urban populations, enhance a city’s environment and help build a more resilient food system.”

Sheffield comprises some 36,800 hectares (nearly 91,000 acres), and the city’s green infrastructure covers 10,600 hectares, or about 45% of the city’s total area. That figure, according to Edmondson and colleagues, is roughly in-line with the average amount of green space in UK cities.

Urban allotments — parcels of land specifically rented out for horticultural production — comprise about 1.3% of Sheffield’s green infrastructure, while domestic gardens currently occupy another 38%. Those areas have the immediate potential to start growing food, if they aren’t already. The researchers write in the study that they identified an additional 1,192 hectares, or about 11% of the city’s green infrastructure, that is “potentially suitable for allotment-style growing,” as well as an additional 404 hectares, or 4% of green space, that could be used “for community garden-style growing.”

Altogether, the researchers calculated that there are about 98 square meters per Sheffield resident that could be opened up to soil-based horticulture: 71 square meters in domestic gardens and allotments and 27 square meters in other green infrastructure. If all of this green space was used to grow food, it could supply approximately 709,000 people — or 122% of the population of Sheffield — with their “five a day.”

The researchers note that this is an upper estimate of the land available to be converted to horticulture, as all of the green spaces they identified might not actually be usable for gardening. Still, they point out that if even one-fourth of that area was able to be converted to gardens, that would equal the 23 square meters per capita that are currently used nationally for commercial horticultural production in the UK. What’s more, the researchers found that devoting an even more realistic 10 percent of domestic gardens and other available green spaces to food production while maintaining current allotment land could provide 87,375 people — 15 percent of the population of Sheffield — with sufficient fruit and vegetables for a healthy diet.

Most of Sheffield’s green infrastructure is located in suburban areas, but Edmondson and co-authors also looked at the potential for soil-free farming on rooftops, which could utilized methods like hydroponics, in which plants are grown in a nutrient solution instead of soil, or aquaponics, which combines the raising of aquatic animals with hydroponics.

According to the study, Sheffield’s commercial city center encompasses 229 hectares, with buildings covering 58% of that area and flat roofs that could potentially be the site of soil-free horticultural operations covering 24%. (Again, the researchers caution that this is an upper limit of the available area, as not all flat roofs will be usable.) That comes out to just 0.5 square meters per Sheffield resident, but the researchers say that the high-yields possible with soil-free production systems could allow those spaces to contribute substantial amounts of fruits and vegetables.

“It will take significant cultural and social change to achieve the enormous growing potential of our cities — and it’s crucial that authorities work closely with communities to find the right balance between green space and horticulture,” Duncan Cameron, director of the Institute for Sustainable Food at the University of Sheffield and a co-author of the study, said in a statement. “But with careful management of green spaces and the use of technology to create distribution networks, we could see the rise of ‘smart food cities’, where local growers can support their communities with fresh, sustainable food.”

CITATION

• Edmondson, J. L., Cunningham, H., Tingley, D. O. D., Dobson, M. C., Grafius, D. R., Leake, J. R., … & Stovin, V. (2020). The hidden potential of urban horticulture. Nature Food, 1(3), 155-159. doi:10.1038/s43016-020-0045-6

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