This paper offers an exploratory overview of different research literatures examining the relationship between urban nature or green space on the one hand, and marginalized, stigmatized, and illicit activities on the other. We situate this discussion within the geographic literature concerning assemblage theory and informality, and apply these concepts to urban green space. We offer some comparative examples from Detroit and Berlin, two cities known for their green space and illicit activity, but with very different histories and cultural contexts. For this purpose, we draw on our own primary research in both Detroit and Berlin, examining how the dynamics of these interactions produce diverse and distinctive urban places in some cases and associations of danger or insecurity in others, sometimes both simultaneously. We utilize diverse methodologies, including qualitative interviews and focus groups, mobile explorations, photography, and sketching to provide examples of spaces as complex assemblages of actors with diverse, emergent potentials. We conclude by contending that green spaces and urban nature belong on the same map as studies of informal and illicit activities, adopting a more fluid conception of the shifting relationship between people and green space in the evolving city.