Drawing on ethnographic fieldwork in Montreal, this article examines the ways in which urban dwellers and activists engage with the living materialities of wastelands to illuminate evolving ecological imaginaries and their political potentials. I focus on a seemingly marginal topic—urban weeds—to explore how human–weed relations can help us situate contemporary environmental concerns within longer histories of spatial violence, ecological degradation and settler power relations. Shifting perceptions of invasive and native weeds unsettle normative frameworks of urban biodiversity and reveal how polluted ecologies can be reinterpreted as sites of value and resistance. Here, I use wasteland activism to define grassroots efforts to protect unconventional, often stigmatized forms of urban nature from erasure within ongoing processes of urban redevelopment. Wasteland activism not only challenges official green transition narratives but also produces alternative visions of ‘worthy environments’ that expose the inherent contradictions of top-down narratives of repair and growth. In contexts where industrialism, far from belonging to the past, is very much an ongoing project, political weeds embody the disjuncture between institutional promises of green development and the slow work of building living presents amid enduring contamination.