Résumé : Urban agriculture is in vogue and unfolds in a diversity of ways, which imply, amongst others, the development of professional activities. From 2015 to 2018, two participatory action research projects have been running in Brussels questioning the viability of small-scale urban market gardening as a way to earn a living, all the while producing food more sustainably. Their focus is on the start-up phase of market-garden farms. We followed a transdisciplinary research setup to reinforce the reflexivity of these market gardeners, and uncover several “knots” these market gardeners face along their start-up trajectory. We define a “knot” as a thematic whole of tensions, compromises and/or adaptations market gardeners struggle with while putting into practice their aspirations. Three thematic knots are presented and discussed here: strategies to access land, the mechanization dilemma and the role of volunteering. To cope with these knots, the trajectory of market gardeners in the start-up phase shows strategic bends and turns so as to stay afloat financially as a business in the short term, yet without getting rid of the knots in the longer term. This work shows that solving the challenges (knots) in the search for long-term sustainability of this type of projects extends far beyond the individual struggles of starting market gardeners. It begs for the reconstruction of a community of practices embedding these neo-farmers, that can be fostered through building an enabling legal, financial and political environment.