Considering global trends such as climate change and resource scarcity, a major challenge of future cities will be to reduce urban footprints. Moreover, cities have to become or remain livable for their inhabitants and offer social and economic opportunities. Thus, reconnecting food production and cities offers promising potential. The diffusion of urban farming reflects a rising awareness of how food and farming can shape our cities. A growing number of urban farming projects exist in and on urban buildings, including open rooftop farms, rooftop greenhouses and indoor farming. These projects are characterized by the non-use of land or acreage for farming activities. We use the term ‘Zero-Acreage Farming’ (ZFarming) to represent these farms. The objective of this paper is to: (1) illustrate and systemize present practices of ZFarming and (2) discuss specific novelties of ZFarming in the wider context of urban agriculture. We analyzed 73 ZFarms in cities of North America, Asia, Australia and Europe using a set of criteria, and developed a typology of ZFarming, complemented by in-depth interviews with pioneers in rooftop farming in New York. The results illustrate that ZFarming generates innovative practices that may contribute to a sustainable urban agriculture. Besides growing food, it produces a range of non-food and non-market goods. It involves new opportunities for resource efficiency, new farming technologies, specific implementation processes and networks, new patterns of food supply and new urban spaces.

Despite extensive literature on the socio-cultural services of urban open spaces, the role of food-producing spaces has not received sufficient attention. This hampers advocacy for preserving and growing urban agricultural activities, often dismissed on justifications that their contributions to overall food supply are negligible. To understand how the social benefits of urban agriculture have been measured, we conducted a systematic review of 272 peer-reviewed publications, which drew on insights from urban agriculture sites in 57 different countries. Through content analysis, we investigated socio-cultural benefits in four spheres: engaged and cohesive communities, health and well-being, economic opportunities, and education. The analysis revealed growth in research on the social impacts of gardens and farms, with most studies measuring the effects on community cohesion and engagement, followed by increased availability and consumption of fruits and vegetables associated with reduced food insecurity and better health. Fewer studies assessed the impact of urban farming on educational and economic outcomes. Quantifying the multiple ways in which urban agriculture provides benefits to people will empower planners and the private sector to justify future investments. These findings are also informative for research theorizing cities as socio-ecological systems and broader efforts to measure the benefits of urban agriculture, in its many forms.

Alternative food networks (AFNs) are growing in number and relevance in Germany. Those networks include new models of production and distribution, such as food cooperatives (FoodCoops), self‐harvest gardens or community‐supported agriculture (CSA) schemes. AFNs, as an alternative to conventional food supply systems, are characterized by a close producer‐consumer interaction. They are typically located within urban or peri‐urban areas. The study aims to identify the rationale and motivation of urban residents in participating in AFNs and developing a consumer typology. We also assess whether AFNs potentially lead to collective action with societal impact. Therefore, we conducted a qualitative content analysis based on 18 interviews with members of existing AFN projects in three German metropolitan regions. Our results revealed that the willingness of urban consumers to participate in AFNs is driven by a broad range of motives. They include personal desire for high‐quality food (in terms of taste or freshness) and health reasons, but also political or environmental motives (opposition to conventional agriculture or short transport distances). Furthermore, consumers often want to support a certain farmer and his/her philosophy or they appreciate the community‐building aspect. Three different consumer types were derived from the motive combinations. Many consumers communicated a sense of belonging to a societal movement, however, our study revealed a lack of organization and collective action. Although AFNs can influence the consumption patterns of individuals, their potential to induce social change and to challenge traditional models of consumption in the near future does not appear to be high.