This paper explores the role of trust in mosaic governance (MG) and is based on in-depth case studies in three municipalities with green volunteers and municipal planners in three municipalities in Denmark. MG refers to a normative governance design focused at stimulating the reflexive co-creation and management of natural areas. Results show that trust is crucial for successful collaboration between municipalities and green volunteers, and hence the unfolding of MG. Municipalities with higher levels of volunteer engagement report greater trust between volunteers and public officials. We show how different kinds of trust (institutional, procedural, rational, and affinitive) influence how collaborations are organized, and how the institutional context influences the possibilities for green volunteer engagement. Trust comes into play in different places and phases of MG and can be said to be the lubricant of MG.