Horticultural interventions may reduce adults' depressive symptoms: A systematic review of randomized controlled trials

We conducted a systematic review to examine the effect of horticultural interventions (e.g., planting or taking care of plants) on people's depressive symptoms as assessed by depression outcome measures. On January 19 of 2022, the databases MEDLINE (PubMed), PsycArticles (APA), SCOPUS (Elsevier), Google Scholar, and ClinicalT rails.gov were searched from inception. The decision to include or exclude studies in the full text, the data extraction, and the risk of bias assessment were performed by two researchers. We identified 20 randomized controlled trials (RCTs) (n = 998 participants; all adults), from nine different countries. Overall, we found evidence that some horticultural interventions plus usual care (i.e., continuing normal routine for healthy people or treatment for unhealthy ones) may reduce depressive symptoms more than usual care alone, with most studies suggesting a moderate (Hedges'g = 0.5) or large effect (g = 0.8). The percentage of participants who dropped out from any of the horticultural interventions ranged from 0% to 40% and only one study reported adverse events (i. e., fatigue and tiredness) related to the intervention. Except for one study, all studies had some risk of bias due to design limitations, such as lack of participants' blinding and/or a prespecified analysis plan. Our findings suggest that some horticultural interventions are effective and safe to use as a complementary strategy to reduce adults' depressive symptoms. More RCTs are needed to understand how specific participants and intervention characteristics can alter the effect of horticultural interventions on depressive symptoms.