The notion and assessment of ecosystem services (ES) values is becoming an established part of the discourse regarding urban green space performance. Yet, underlying factors enabling ES values are still poorly understood. We assume the production of ES value crucial for environmental stewardship in cities, and aimed in this study to uncover their key enabling factors. This study has been developed on a broad data base including a survey (n = 201), interviews (n = 46), field observation and remote sensing from 27 urban gardens in Barcelona, Spain, including municipal ‘allotment gardens’ and ‘civic gardens’ emerging from bottom-up initiatives. In a first step, we distinguished different urban gardens types regarding the ES values they provide. In a second step, we tested specific garden characteristics including (a) user profiles, (b) biophysical garden properties, and (c) in- stitutional settings for their specific importance to trigger ES values. Results showed ES values to significantly differ with the types of gardens. For example, classical allotment gardens are more likely to provide recreational values, while emerging civic gardens are more likely to produce place-making and social cohesion. A main finding from our study is the importance of social and institutional garden characteristic as enabling factors of ES values. Results indicate, for example, a correlation between childhood experiences and a higher appreciation of ES. Our results further indicate that civic gardens with broader property rights and decision-capacities are more likely to enhance stewardship action. In providing a differentiated understanding of the ES value(s) of urban gardens, this study highlights the potential for green space planning in cities to steer the stewardship of urban gardens by providing institutional and physical space for civic gardening initiatives.