Millions of gardeners extol the health benefits of gardening. Not unexpectedly, hundreds if not thousands of scientific studies, mostly observational, qualitative, not randomly controlled, and many with small numbers of participants have reported favorable outcomes resulting from gardening treatment interventions. Yet, individually, most of these studies have been insufficient to conclusively establish a robust scientific basis or determine the magnitude of the curative or restorative power accruing from such people-plant treatments. Additionally, faithful confirmatory replication of any gardening study by different research groups is virtually non-existent. Enter the meta-analysis. A meta-analysis is a statistical procedure that integrates the results of several independent studies. Meta-analysis, when properly executed, provides the strongest freedom from various biases in clinical evidence. A meta-analysis can provide a more precise estimate of treatment outcome effect size and increase the robustness above that of individual studies’ results. Therefore, it can yield conclusive results when individual studies are inconclusive.
At least nine meta-analyses on gardening and horticultural therapy studies have been published, including six in the past two years. In future installments of this column, I will highlight some of the recent meta-analysis studies.
The meta-analysis by Spano1 and colleagues in 2020 examined studies of community gardening and horticultural interventions on participant psychosocial well-being. Following a systematic search of the literature(PRISMA2), seven individual studies reporting 22 treatment effect size estimates were included in the meta-analysis. Sample sizes ranged from 45 to 978 participants, and average ages ranged from 45 to more than 80. The Spano study found support for publication bias and heterogeneity in the selected studies, meaning studies lacking statistically significant results appear to be underreported (unpublished), and variation of outcomes between studies was more extensive than expected by random chance. Nevertheless, the analysis showed that community gardening or group horticultural activities provided a “significant positive effect” on participants’ psychosocial well-being over 11 different treatment outcomes. In particular, the study underscored the positive effects of community gardening as a means for social interactions, mutual support and community cohesion. Spano and colleagues concluded: “Although our results must be taken with caution, they would seem to suggest a further applied implication of these interventions (i.e., psychosocial functioning aimed to improve citizens’ quality of life and sense of community).”
1Spano, G., D’Este, M., Giannico, V., Carrus, G., Elia, M., Lafortezza, R., Panno, A., & Sanesi, G. (2020). Are Community Gardening and Horticultural Interventions Beneficial for Psychosocial Well-Being? A Meta-Analysis. International Journal of Environmental Research and Public Health, 17(10), 3584. https://doi.org/10.3390/ijerph17103584
2PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses. See http://www.prisma-statement.org/
Charles Guy, Emeritus and Courtesy Professor
Department of Environmental Horticulture, University of Florida