Techniques and crops for efficient rooftop gardens in Bologna, Italy

Urban rooftop farming favours local food production. Although rooftop farming is perceived as a sustainable system, there is a lack of quantitative studies. There, we set up experiments in the community rooftop garden of a public housing building in Bologna, Italy, between 2012 and 2014. We grew lettuce, a leafy vegetable, using three techniques: nutrient film, floating hydroponic and soil cultivation. We also grew tomato, chilli pepper, eggplant, melon, watermelon on soils. Data was analysed by life cycle assessment for environmental and economic performance. Results reveal that the best techniques of lettuce cultivation to address global warming were floating in the summer, with 65–85 % less environmental impact per kilogran than nutrient film; and soil production in the winter, with 85–95 % less environmental impact. Furthermore, floating production was 25 % cheaper in summer, and soil was 65 % cheaper in winter, compared to the nutrient film technique. For soil production, eggplants and tomatoes showed the best environmental performances of about 74 g CO2 per kg. Eggplant production in soil was cheapest at 0.13 € per kg.