In the June 20th, 2025, edition of the garden’s Newsletter1, I wrote about a compelling systematic review and meta-analysis out of the United Kingdom by Wood, Barton, and Wicks2 of 11 social and therapeutic horticulture studies that together quantitatively showed large and statistically significant treatment group effect size differences relative to comparator groups for depression and six studies that showed moderate and significant treatment effect size differences for anxiety.
The findings and conclusions of the Wood et al.2 systematic review and meta-analysis are now further supported by a second independent systematic review and meta-analysis by Kuo and coauthors3 of 13 horticultural therapy (HT) randomized controlled trials (RCTs) involving study populations previously diagnosed with a depressive disorder according to DSM-5, or other standardized diagnostic criteria, or based on a psychiatrist’s diagnosis. The authors also analyzed the treatment effects of HT on participant anxiety, cognitive function, and quality of life. The combined population of the 13 RCTs was n = 960. The two meta-analysis studies of Wood2 and Kuo3 contained only one individual study in common and therefore together sampled a wide range of individual studies.
Kuo et al.3 found that meta-analysis of the HT treatment studies demonstrated statistically improved participant scores for depression, anxiety, cognition, social function, and quality of life. Collectively, participants with depressive disorders (n = 847) receiving the HT treatments exhibited large treatment effects. Positive treatment outcomes for anxiety (n = 372) were moderate to large. Similarly, the treatment effects for cognitive function and quality of life were found to be large.
A potential source of treatment outcome uncertainty in the present meta-analysis was the occurrence of small participant sample sizes in most of the included studies. While meta-analysis combines multiple studies to encompass larger sample sizes, the smaller sample sizes of individual studies do, to some degree, constrain the statistical robustness of the outcomes.
A unique finding of the Kuo et al.3 study was that moderate-to-large treatment effects for HT were achieved over 4-8 weeks, and large effects were observed for treatments lasting more than eight weeks. This finding suggests that greater treatment outcomes can be achieved with longer treatment regimes.
The two systematic reviews and associated meta-analyses provide unquestionable evidence that the time has come for the therapeutic effectiveness of horticultural therapy to be rigorously tested with large-scale, well-designed, properly blinded, multi-institutional randomized controlled trials. The well-being and quality of life of society await the benefits of engaging in horticultural activities that anecdotally have been known for millennia.
1https://doi.org/10.1016/j.ctim.2025.1032292
2Wood, C.J., Barton, J., Wicks, C.L. (2025). Effectiveness of Social and Therapeutic Horticulture for Reducing Symptoms of Depression and Anxiety: A Systematic Review and Meta-analysis. Frontiers in Psychiatry, 15, 1507354. https://doi.org/10.3389/fpsyt.2024.1507354.
3Kuo, Y.Z., Yu, Z.S., Li, Y.Z., Chen, M.D., Lee, Y.W., Lin, P.Y., Chen, T.T., Hsu, C.W. and Chen, C.R., (2025). Efficacy of Horticultural Therapy on Symptoms and Functional Outcomes in Individuals with Depressive Disorders: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Complementary Therapies in Medicine, p.103229. https://doi.org/10.1016/j.ctim.2025.103229
Charles Guy, Emeritus and Courtesy Professor
Department of Environmental Horticulture, University of Florida
Steering Committee, Wilmot Botanical Gardens, University of Florida