Growing cities face severe land use conflicts. Urban expansion and the densification of existing built areas are increasing the pressure on green spaces, which are key for climate change adaptation. Planning procedures embroiled in these land use conflicts are often complicated and slow. This is due to the increasing complexity in planning processes, which involve a multitude of stakeholders and decision-makers, whose responsibilities are not always entirely clear. Governance-oriented forms of decision making with horizontal structures are often required, but these also entail challenges. In our study, we ask how climate adaptation through urban green spaces can be integrated into planning processes. The study is based on a methodological combination, including document analysis and qualitative interviews with administrative staff. The City of Munich, a rapidly growing German city, serves as a case study. The results show different collaborative arrangements in four planning arenas and demonstrate how these structures support or hinder climate change adaptation mainstreaming. We conclude that hierarchical structures impede horizontal collaborative arrangements and shed lights on mechanisms reinforcing these structures. For large administrations, informal meetings and coordinating units are effective in fostering interdepartmental cooperation.