The creation of outdoor learning spaces (OLS) such as school gardens is increasing in frequency in elementary and secondary schools in Canada. Previous research has indicated that students benefit from learning in OLS, but little is known about teachers' perceptions of their experiences using school gardens or other OLS. Given that teacher buy-in is essential for effective use of these learning environments, better understanding of the factors which affect teachers' adoption and continued use of OLS is needed. Thus, we interviewed elementary- and high-school teachers who used school gardens in Richmond, British Columbia, Canada, to explore their perceptions of their experiences of using school gardens and other OLS. We analysed interview transcripts, guided by Roger's Diffusion of Innovations theory, and identified key factors influencing teachers' adoption of school gardens or other OLS in their pedagogy: personal values, gardening experience, environmental education, and administrative support. Teachers' continued use of various OLS was supported by students' enthusiasm for learning in those spaces. Barriers to using OLS included lack of administrative support, principals' disapproval, and lack of professional development regarding their use. Insights from this study can be applied to support teachers in the adoption of school gardens and other OLS in their teaching.