Green infrastructure (GI) sits at the intersection of planning theory and practice, offering nature-based solutions to pressing environmental, social, and economic challenges. Yet GI lacks a coherent epistemic base. Key claims cannot be justified in consistent ways or evaluated using shared standards. This paper traces the evolution of GI knowledge across its first 30 years (1995–2025), drawing on a Scopus dataset of 10,573 publications. Using longitudinal bibliometric analysis alongside a Sociology of Knowledge framework and boundary work theory, we examine how GI knowledge is socially constructed, how power and influence are distributed among competing epistemic communities, and what this means for planning's capacity to mobilise GI in policy and practice. Our findings reveal three main disciplinary clusters contributing to GI framings — Ecological, Urban, and Hydrological. Each is diverging rather than converging. GI thinking began as a field with interdisciplinary promise but increasingly is exhibiting growing multidisciplinarity: joint puzzle-solving is giving way to parallel problem-solving. As disciplines work together in different ways, so hierarchies come into play. Ecologically-oriented researchers hold structural primacy. Urban and Hydrological researchers are epistemically distant. Boundary organisations play a crucial but underexplored role in synthesising knowledge across these divides and translating it into actionable planning frameworks.These developments raise concern that GI risks becoming a panacea concept, vulnerable to political co-option and resistant to the kind of coherent, evidence-based planning that long-term, place-based approaches demand. We conclude with a research agenda calling for a more clearly demarcated GI ontology to strengthen planning's intellectual and practical foundations.