A Systematic Review of Studies Evaluating the Effectiveness of Horticultural Therapy for Increasing Well-Being and Decreasing Anxiety and Depression

Background and Purpose

The purpose of this study was to evaluate the effectiveness of horticultural therapy (HT) as a potential mental health intervention for social work clients. According to biophilia theory, human well-being suffers when a preponderance of time is spent dwelling indoors with little to no outdoor exposure. Instead, the theory proposes that spending time in the natural environment promotes social, emotional, and physical wellness. As a wellness-based, holistic intervention, HT can easily be implemented in a variety of social work settings. As described by the American Horticultural Therapy Association (AHTA), HT promotes physical exercise, a sense of belonging, and enhances social connectedness for people experiencing mental health concerns.

Methods:

This study is a systematic review of published research on the effectiveness of horticultural therapy for increasing well-being and reducing anxiety and depression. A Boolean search term was constructed as follows: (“symptoms of mental illness” OR anxiety OR stress OR depression OR panic) AND (Horticultural Therapy OR Gardening OR Nature-based therapy OR Ecotherapy OR Therapeutic horticulture OR Green Therapy OR Greening) AND (Random* OR Controlled Clinical trial* OR blind OR placebo OR RCT). CINAHL, Medline, and PsychInfo databases were searched yielding a total of thirty-three articles. Further screening excluded studies not measuring mental health, mental illness, or wellness-related outcomes. This resulted in 11 articles that were used for meta-analysis. Standardized mean differences were meta-analyzed using R (version 4.0.4) with the metafor package (version 3.0.2). A quality of study rating form was completed to evaluate overall study quality and to extract other information for the systematic review.

Results:

Based on the random-effects model, the estimated average standardized mean difference (SMD) on well-being outcomes was μ^=0.5881 (95% CI: −0.1015 to 1.2778). For anxiety outcome measures, the average SMD was μ^=−0.5722 (95% CI: −1.0161 to −0.1283). For depression outcome measures, the SMD was μ^=−0.4166 (95% CI: −0.7236 to −0.1096). Results indicated significant effect sizes for improvement of mental illness symptoms. Though not statistically significant in this meta-analysis, the prediction interval for well-being outcomes suggested that HT is likely effective at improving well-being with some populations. Heterogeneity analysis indicated that HT likely produces different effect-sizes with different populations.

Conclusions and Implications

HT is an effective intervention for reducing mental illness symptoms in a variety of social work client populations. This review included studies of the effectiveness of HT with white-collar workers, adults with severe mental illness, post-menopausal women, caregivers of elderly persons with dementia, elderly people with memory problems and depressive symptoms, recovering stroke patients, elderly nursing home residents, and people diagnosed with Alzheimer’s type dementia and apathy. Because social workers provide services to all of these populations, HT is a viable intervention for use by social work practitioners. HT seems especially beneficial to those who do not typically experience much contact with nature (e.g., long-term-care patients, persons with agoraphobia or other mental disorders that result in confinement, etc.). Further research is needed to replicate findings so that effect-size differences between sub-groups can be better understood.