This paper examines informal urban gardening practices within a 70-year-old industrial neighbourhood in Zhengzhou, central China, employing the conceptual framework of ‘annexed common space for private green infrastructure’ (ACS-PGI). Through urban morphological and typological analysis, it interrogates how historical institutional legacies, urban land tenure regimes, local governance structures, socio-spatial configurations and cultural-agricultural traditions collectively inform and sustain these grassroots greening practices. Adopting a structural attribution system framework, the study advances a comprehensive understanding of the multifaceted structural determinants underpinning informal gardening. Departing from Western-centric interpretations that often frame such practices as acts of political contestation, the Zhengzhou case elucidates a historically embedded, socially legitimised and spatially articulated phenomenon rooted in collective memory, communal land-use rights and tacit state tolerance. This research contributes to urban socio-environmental scholarship by underscoring the necessity of situating informal urban greening within its distinct institutional and cultural-historical context, thereby offering critical insights for the theorisation of sustainable urban green infrastructure and community agency.</p