The promotion of spontaneous vegetation is recognized as a promising way to develop urban biodiversity at multiple scales. However, enhancing spontaneous vegetation in highly anthropized spaces such as cities can lead to resistance from the various urban actors who plan, manage, and use the city. An integrated approach analyzing the links between ecological, psychosocial, governance, and management issues is thus required. Here we used complementary methods (focus groups, interviews) to analyze the relationships of municipal field operatives and city dwellers to spontaneous vegetation in the streets of a French medium-sized city. We show that municipal elected officials and service director move towards a biodiversity-friendly strategy, but that the management system at all hierarchical levels must be engaged with to achieve a shared and collaborative transition to sustainability. While field operatives are rather favorable to spontaneous vegetation, their practices and their ability to change are highly dependent on psychosocial, organizational, and technical parameters that have to be aligned with ecological objectives. Concerning city dwellers, the majority holds a positive view of spontaneous vegetation, yet a considerable proportion of them seem indifferent to this vegetation. The provisioning of ecological information in situ (i.e., stickers with plant information on pavements) moderately improves their perceptions of spontaneous street vegetation. This educational approach should be accompanied by other approaches to amplify the effect for changing attitudes. These differing results are of timely interest to help devise and build an integrated socio-ecological system, and to find social and organizational levers to improve people–nature relationships in the city.