CONTEXT: There is a widespread acknowledgement that research should be supporting farmers' transition processes towards more sustainable farming systems by applying participatory research approaches. However, scientific papers dealing with participatory research on farming systems seldom include a reflection on the outcome of these processes or the methodological implications of such an aim. OBJECTIVE: The aim of the research process presented in this paper was together with a group of Danish farmers to explore the potential use of species mixtures in their own farming contexts by following several participatory research principles. METHODS: 16 farmers volunteered to participate in the joint research process initiated by on-farm experimentation with a diverse catch crop mixture. The paper presents seven activities of the research process carried out using a variety of quantitative and qualitative methods such as an applied game, farm visits, on-farm experimentation, common evaluations and discussions. The authors have analysed the process as a case study using three levels of empirical observations and descriptive narratives. RESULTS AND CONCLUSIONS: The authors found that the farmers were involved throughout the two-and-a-half year study period and experimented with species mixtures using different strategies. With the researchers, they identified and challenged structural, agronomic, technical and social barriers, and investigated the potential of species mixtures adapted to local conditions. The case study revealed that both farmers and researchers need to take on new roles, with farmers needing to invest their resources and time to come up with valuable data and knowledge. Similarly, researchers need to facilitate the explorative research process by meeting farmers' needs while being able to draw valuable scientific conclusions. This requires new skills that have not traditionally been valued in agricultural sciences. SIGNIFICANCE: This study demonstrates that the barriers to changing farmers' cropping practices are not necessarily due solely to technical challenges or a lack of knowledge. Instead, researchers need to look beyond the farm gate and involve other actors in unlocking the potential of an increased use of species mixtures.