Citizen social science has been developing in meaning and prevalence over the past few years, building on experiences with both citizen (natural) science and established social science methods such as participatory action research. However, most of the debate is still at the conceptual level, with strong calls for more empirical insight. Here, we critically examine the promises and challenges of citizen social science, based on two small-scale, co-created and locally embedded projects on people’s relationships with urban greenspaces and community food growing, conducted as a collaboration between professional and citizen social scientists. Our findings illustrate the complexity of such research in practice and identify five dilemmas that arise from tensions between the aspirations and hopes associated with co-created citizen social science, and the pragmatic and procedural realities of citizen research in practice. We argue that citizen social science projects will have to actively engage with these in order to be successful.