Thee importance of connectedness in laying the ground for social-ecological transformations or in spreading new ideas and practices for transformation is increasingly recognized. However, the role of networks in supporting the emergence and growth of seeds (initiatives with the potential to positively shape the future) has not yet been comprehensively studied empirically. To this end, we introduce a novel concept, the seeds’ substrate, to characterize: (1) the relationships among a network of seeds, (2) the support needed for seeds to appropriately scale and coalesce, and (3) the actors that enable and provide support. The seeds’ substrate concept was theoretically informed and empirically derived by using a case study of an ongoing coalescing process. On this basis, we derived several categories and definitions for seeds interactions, types of support, and supporting actors that collectively constitute the seeds’ substrate. Specifically, we identified seven types of interactions between seeds, nine types of support, and 14 different categories of supporting actors. Furthermore, we presented a multi-level network approach to analyze the seeds’ substrate and test specific hypotheses within this modeling approach. By putting the seeds’ substrate concept into practice in an ongoing coalescence process involving 11 seeds around the small-scale fisheries food system in Uruguay, we identified the network of seeds and the constellations of actors and interactions that preceded efforts to deliberately foster a seed coalition. This allowed us to anticipate synergies and conflicts and to identify key supporting actors that structure the seed substrate. In addition, we derived a comprehensive baseline against which to quantitatively compare the unfolding of the coalescence process over time. This paper contributes to filling a gap in the Seeds of Good Anthropocenes literature and unpacks a key but largely unexplored subprocess of its theory of change: the transition from periods of experimentation to periods of coalescence. We expect the seeds’ substrate concept to be useful in a wide and diverse range of social-ecological contexts.