Despite strong evidence on the role of nature in supporting positive mental health outcomes, a variety of challenges and barriers exist for people with severe mental illness (SMI) in accessing nature-based interventions. While interprofessional collaboration (e.g., occupational therapy and horticultural specialists) has previously been recommended, people with SMI as the end users may not always be included in research at a meso-level (e.g., organisation, community). This co-production study aims to explore the potential use of nature-based interventions to improve quality of care and promote health outcomes in the short and longer term for people with SMI across a patient care pathway from inpatient care through to community referral. Through Participatory Action Research (PAR) we will work with co-researchers (to include people with lived experience of SMI, occupational therapy teams, and nature-based providers) to identify the salient barriers, challenges, opportunities and facilitators to nature-based interventions for people with SMI.