There is little robust quantitative evidence on how community gardens impact on physical activity and other health-related behaviours. This natural experiment study aimed to examine the effects of a community garden within a Chinese neighbourhood on health-related behaviours during the COVID-19 epidemic. The study design was a repeat cross-sectional pre–post study, assessing differences between the non-epidemic period and epidemic period. Camera-based systematic observations were conducted at two locations within a community garden. A total of 180 h of video recordings were collected and coded by two researchers during a “non-epidemic” period when there were no COVID-19 restrictions (120 h) and the “epidemic” when COVID-19 restrictions were implemented (60 h). Observations of these video recordings assessed the total number of users, physical activities (Sedentary, Walking, Vigorous), social interactions (Connect), and people taking notice of the environment (Take Notice), followed by a breakdown of observed gender and age group. Data were analysed using paired t-tests and Wilcoxon signed-rank tests, comparing outcomes during the epidemic period and non-epidemic period. Results showed a significant increase in total number of users during the epidemic, particularly in females, older adults and children. Sedentary and moderate physical activities were significantly higher during the epidemic period. The increase in the total number of users of the community garden during the 2022 epidemic outbreak in Suzhou shows the importance of community gardens as a primary space for outdoor activities. This robust natural experiment study demonstrated that the community garden contributed more to physical activity, such as walking, but less to interactions between people (connecting) or people–place interactions (taking notice of the environment). More natural experiment research on community gardens like this is needed to better understand how the health and well-being benefits of community gardens can be maximized.