The need for social-ecological systems to become more adaptive is widely acknowledged. Social effects generated by participatory planning have been claimed to contribute to this transformation, but little empirical evidence is available that backs up or opposes this notion. We aimed to offer some insights regarding questions as to which social effects are formed in participatory planning processes and at what costs, and to then discuss their contribution to the transformation toward more adaptive social-ecological systems based on empirical evidence. Consequently, we investigated the social effects of participatory planning processes, including the social learning processes leading to them. We conducted semistructured interviews with members of advisory groups involved in river engineering projects in Switzerland. Our results indicate that participatory planning processes can somewhat contribute to maintaining and spreading knowledge and social capital among individuals in a planning group, and this may help them collectively deal with new and complex challenges. However, it is costly in terms of time and patience to build up ecological knowledge, communicative capacities, and trust, with the latter also eroding over time. Overall, we conclude that the contribution of participatory planning via positive social outcomes to the transformation toward adaptive capacity social-ecological systems is smaller than optimists might hope. However, other forms of planning very likely result in no social effects or even the destruction of social capital. Participatory planning, in contrast, can offer the conditions for relational and cognitive learning contributing to the maintenance of social and political capital. Based on our results, we suggest shifting resources from technical to communicative aspects of planning processes and implementations. We recommend that project leaders provide stakeholders with firsthand information about projects, explain rationales and data behind decisions, and clearly communicate that stakeholders do not have decision making competence to support participants in finding their roles in similar participatory planning settings.