Can rooftop gardens grow city’s vegetables?

2014-08-20 11.06.46 Rooftop gardens in cities could provide more than three quarters of the vegetables consumed in them, a case study from Bologna, Italy, suggests. If all suitable flat roof space was used for urban agriculture, rooftop gardens in the city could supply around 12 500 tons of vegetables a year whilst also providing a range of ecosystem services, the researchers say.  

Source: Orsini, F., Gasperi, D., Marchetti, L., et al. (2014). Exploring the production capacity of rooftop gardens (RTGs) in urban agriculture: the potential impact on food and nutrition security, biodiversity and other ecosystem services in the city of Bologna. Food Security 6(6): 781-792. DOI: 10.1007/s12571-014-0389-6.

Any unused roof space in a city represents an opportunity to add to that city’s green infrastructure. Urban green spaces and infrastructure, which include rooftop gardens, offer benefits for both wildlife and people. Not only can they produce food for city-dwellers, they can increase urban biodiversity and link together to form green networks, acting as corridors for wildlife. They can also reduce a city’s ecological footprint by filtering polluted air, absorbing noise and CO2 emissions, and controlling temperature by shading.

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In 2010, Bologna became the first Italian city to test rooftop vegetable gardens on public buildings, as part of a project led by the local authority, university and a non-profit organisation. Researchers followed the trial over three years between 2012 and 2014.

During this time, rooftop gardeners grew lettuce, black cabbage, chicory, tomato, aubergine, chili pepper, melon and watermelon, either in plastic pipes, recycled pallets filled with compost or on polystyrene panels floating in tanks, also made from recycled pallets.

On average, the recycled pallet system with compost produced the most vegetables for the amount of space used, a third more than the floating system and more than twice that of the pipe system. However, the amount of each type of vegetable produced by each system in each season varied considerably and the pipe system made use of hanging space when surface area was limited.

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From the results of the trials, the researchers were able to design an optimal growing system for a 216 m2 rooftop garden, which combined elements of each system in order to maximise productivity throughout the year. This included slightly more floating structures than pallets, as well as pipe systems along the railings. The researchers estimate that this hypothetical garden could produce more than three tonnes of vegetables per year.

Next, the researchers estimated the potential productivity of a network of vegetable gardens occupying all suitable flat roof space across the city. They used digital maps and computer-aided design (CAD) software to identify all the unused flat spaces on Bologna’s roofs and terraces.

Their calculations suggest that, if all available space (about 0.82 km2) was utilised, rooftop gardens in Bologna could produce around 12,500 tonnes of vegetables. This means that, based on actual consumption data for the city, rooftop gardens could meet 77% of residents’ needs for vegetables.

If all the spaces identified in the study were turned into gardens, they could capture an estimated 624 tons of CO2 each year. The study’s authors also mapped the connections between spaces that were within 500 m of each other showing that rooftop gardens could create a network with a total length of 94 km of green corridors for wildlife, including pollinating insects. The 500 m distance was considered appropriate by the researchers because most common bee pollinators have a flight foraging distance of 750–1500 m.

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Images above are of the London’s Southbank Centre roof garden, created as a partnership between Southbank Centre and the Eden Project, it was built from scratch by the Grounded gardening team from Providence Row Housing Association (PRHA) working with colleagues from Eden.  Unusual foods such as blue potatoes, narga peppers as well as a mini olive grove are being grown. They also aim to add more greenery to Southbank Centre, training vines, hops and ivy over the concrete walls. Raised beds, wild and pollinating flowers and the lawn will also be maintained.

Images: Carine Brannan

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6 comments

  1. Pingback: Can rooftop gardens grow city’s vegetables? | Landscape Interface Studio | WORLD ORGANIC NEWS
  2. Marc van Rooij

    The article is very interesting, however in this case there are issues not taken in consideration, such as the fact many metropolitan arrears are located in less favourable condition for growing vegetables in open air. Also the contamination with pollution is not taken in consideration. Food security is not just an issue of sufficient food, but moreover a question of the right food of good quality. Lead poisoning is a serious issue, there are many other health risks in open air city production not taken in account.

  3. landscapeiskingston

    Community gardeners and urban farmers across North America are using an innovative research toolkit developed in New York City to measure and track the impacts of their work. A small group of gardeners created the toolkit in mid-2013 as part of the Five Borough Farm initiative of the Design Trust for Public Space, a local non-profit incubator for groundbreaking urban planning and design projects. The toolkit is made up of sixteen different methods for collecting data about things like the number of pounds of food harvested in a community garden or the number of children who develop a taste for fresh vegetables after hanging out at a neighborhood farm.

    Currently there is very little data to substantiate the benefits of urban agriculture. Having more concrete information will help make the case for the value of activities so you can advocate to achieve your farm or garden’s goals.

    To download the toolkit: http://farmingconcrete.org/barn/static/resources/DataCollectionToolkit.pdf

  4. Pingback: Rooftop farming: The next steps for development | Landscape Interface Studio
  5. hdelvaux

    The “12500 tonnes for the whole city of Bologna”, covering “77% of residents’ needs for vegetables”, is a useless big-number-non-informative type of communication. How much kg vegetables is that per inhabitant? That’s something relevant, because, do they eat a lot of vegetables in Bologna, or extremely little? Are potatos and onions considered ‘vegetables” or not ? (In Italian context very often not…) etc etc.
    LINK to source, also is dead.
    I like articles that present usefull data, this looks like sensetion journalism… SORRY !

    • landscapeiskingston

      I have updated the link to the full text of this paper. The text in the blog is the abstract and therefore only conveys a broad sweep of the full content of the research paper, ‘Exploring the production capacity of rooftop gardens (RTGs) in urban agriculture: the potential impact on food and nutrition security, biodiversity and other ecosystem services in the city of Bologna’ by Orsini, F., Gasperi, D., Marchetti, L., et al. I’m sure in the full paper will find more detailed analysis of the research undertaken and answers to your questions.

      The Landscapeis blog is keen to explore all areas relating to land use including all aspects of landscape architecture and spatial planning. We highlight articles we think our readers will find of interest. In general the posts are a summary of research and we will add a link to the full paper for those who want to read in more depth….apologies that the link in this instance was not operational but hopefully this is now fixed.

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