PurposeThe scaling of social initiatives is of immense importance for public innovation. A key factor in the scaling process is the institutional environment, which plays a key role in supporting and coordinating the scaling process. This environment can be either homogeneous or heterogeneous, i.e. dominated by a few or a variety of public organizations, norms and practices. Both environments have advantages and challenges. However, the academic understanding of the influence of the institutional environment is limited, and a systematic empirical assessment of the relationship between the type of environment and scaling is lacking. The purpose of this paper is to explore the influence of homogeneous and heterogeneous environments on the scaling process of social initiatives.Design/methodology/approachA comparative qualitative study was conducted in the Dutch social sector, including 48 in-depth interviews with initiators and organizations operating in three different domains – a homogeneous, heterogeneous or mixed environment – in the public sector.FindingsHomogeneous environments are less supportive of scaling social initiatives than heterogeneous environments, as sharing best practices and collaborating with less-familiar organizations is not common. Heterogeneous environments, however, do not provide coordination of the scaling process, with the risk that public funds are used less efficiently and effectively. Institutional environments with a balance of homogeneity and heterogeneity are best suited for scaling social initiatives.Originality/valueBy combining literature from different research areas and conducting extensive empirical research in different domains of the social sector, the authors' study provides a broad and nuanced picture and brings precision to the authors' understanding of the relationships between the institutional environment and scaling in the public sector.