This is one of the most influential papers that I have seen in a long time on the topic of gardening and health by Yang and colleagues1. This study, published in June 2022, was conducted in Korea during the COVID-19 pandemic and aimed to determine whether engaging in outdoor gardening would be feasible and provide therapeutic benefits under the conditions imposed on daily life during the pandemic.
The quasi-experimental design of the study was a before and after treatment analysis and did not include a control group. Although it was not a controlled randomized trial, it is a potentially strong study because the number of participants (>100) is larger than most studies on gardening and health benefits, the high number and duration of gardening sessions (30 – each 3 hours), the quality of the assessments used and the frequency data was collected, and the robust statistical approach to analyzing the data. Also, it was a multi-site study that served to strengthen the veracity of the findings.
Adults responding to a flyer describing the study posted on public bulletin boards and online were screened, and those exhibiting mild depression and/or mild anxiety were included in the study. Potential participants with mobility limitations, communication difficulties, or severe mental health disorders were excluded from the study. The study population demographics were 79% women/21% men, average age 55.5 years with a range of 18->65 years. Over half of the participants had earned a bachelor’s degree, and 53% had been clinically diagnosed with a mental health disorder.
While to be sure there are experimental weaknesses in the study, it still revealed some especially important findings. They show there was very likely to be a strong sex influence on treatment effectiveness with women showing a much larger benefit for indications of depression than men. Older people showed a more substantial positive treatment effect concerning indications of depression than younger people. Treatment effectiveness was reduced for indications of depression and QoL if there was comorbidity of other mental health disorders. While the authors did not comment on it, there was a strong dosage relationship throughout the treatment that had not reached saturation or leveled off for depression and QoL even after 30 sessions.
The treatment effect size Cohen’s d, an indication of treatment effectiveness, was determined and found to be large for depression, medium for anxiety, daily activities, and QoL, and small for mindfulness. Moreover, the mean scores for depression, anxiety, and daily activities were significantly improved after just eight treatment sessions.
Given the experimental design, the influence of the Hawthorne effect cannot be determined, and the placebo effect cannot be ruled out. Those caveats being considered, the results of the present study nevertheless strongly warrants and justifies large-scale randomized controlled clinical trial studies to quantify the actual therapeutic benefits of gardening on mental health, well-being, and the potential overall public health impacts.
1Yang, Y., Ro, E., Lee, T. J., An, B. C., Hong, K. P., Yun, H. J., … & Choi, K. H. (2022). The Multi-Sites Trial on the Effects of Therapeutic Gardening on Mental Health and Well-Being. International Journal of Environmental Research and Public Health, 19(13), 8046. https://doi.org/10.3390/ijerph19138046
Charles Guy, Emeritus and Courtesy Professor
Department of Environmental Horticulture, University of Florida