How does your garden grow? An empirical evaluation of the costs and potential of urban gardening

Urban agriculture is being promoted as an important part of a sustainable food system. Whether urban agriculture can play a significant role in feeding the world's population, however, is unclear. In particular, the literature provides little guidance on how much food could be produced in Western cities. This research addresses some of this gap by presenting the results of a survey conducted with 50 backyard gardeners that explored how much food they produced and what these gardens used in terms of land, labour and capital. Data comes from Guelph ON, a mid-sized Canadian city west of Toronto, and was collected over the 2012 gardening season. Results indicate that home vegetable gardeners produced an average of 1.43 kg of fruit and/or vegetable per m2 gardened. This means that the value of these garden products would be worth $4.58USD/kg if bought in a grocery store. When these data were extrapolated up to the city level, results show that self-provisioning could produce approximately 200,000 kg of food - enough to feed 2900 people. When labour is valued at minimum wage, producing this food required $35.86USD/kg of inputs. When labour is not valued, this dropped to $10.82USD/kg. There are wide variations in the data; the productivity of the most and least productive gardens varied by nearly 2 orders of magnitude (the range was 0.08-5.18 kg/m2 and 0.3 h/kg and 21.9 h/kg). Three key conclusions stand out: (1) there is impressive potential when only the most productive are considered as an illustration of what could be produced; (2) as it is currently practiced, only a fraction of potential production is happening; and (3) for urban self-provisioning to meet its potential, a major increase in the area gardened and gardening skill is required.