Governance of risks to native flora and fauna and agriculture from disease and pests increasingly emphasises the importance of a ‘shared responsibility’ for biosecurity. Few studies, however, have examined factors that influence stakeholders' engagement with such risks and responsibilities, particularly in community, rather than agricultural, settings. In this paper, we focus on a group of stakeholders in a context of heightened regional biosecurity activity, in northern Queensland, Australia. We explore the role that community garden actors may or may not play in biosecurity surveillance. Through interviews with 16 community garden group leaders and local government representatives, we unpack external social factors that contributed to stakeholders' engagement, unengagement or disengagement with and from biosecurity risks. These factors included institutional characteristics such as land tenure and the presence or absence of management policies and guidelines. However, we found that less formal institutional characteristics such as social networks played a greater role in shaping stakeholder engagement. Unengaged stakeholders were typically unaware of risks posed by plant pests and diseases and had limited network connections to relevant government agencies but expressed an interest in learning and participating in biosecurity surveillance networks. Disengaged stakeholders were more knowledgeable of biosecurity risks and had established network connections but expressed a low interest in or willingness to report a potential biosecurity threat. This case study provides insights into important social dimensions of governing risk among stakeholders and offers recommendations to improve stakeholder engagement within biosecurity surveillance networks.