Effect of horticultural therapy on mental health: A meta-analysis of randomized controlled trials

WHAT IS KNOWN ON THE SUBJECT?: Mental health assessment is a common topic in horticultural therapy (HT). Some study findings were contrary to positive findings, although several studies have explored the effect of HT on mental health and reported positive results. There is weak evidence in the benefits of HT based on evidence-based medicine. Stronger evidence of the link between HT and mental health will help in policy making by health policy makers and governments. WHAT THE PAPER ADDS TO EXISTING KNOWLEDGE?: The purpose of this meta-analysis of randomized controlled trials (RCTs) was to explore the effect of HT on mental health. This study is the first meta-analysis of RCTs to provide critical evidence that HT has a positive effect on mental health. The effect size of HT on mental health was medium (0.55). The included studies had no negative effects on mental health. WHAT ARE THE IMPLICATIONS FOR PRACTICE?: HT should be considered a useful therapy to be integrated in healthcare settings by horticultural therapists to improve mental health. In the HT program, indoor and outdoor plant activities, plant-related arts, crafts and other activities were common interventions to improve specific mental health problems through at least eight sessions. ABSTRACT: Introduction HT has been widely used to promote mental health. However, heterogeneity and sample size issues of randomized controlled trials made it challenging to illustrate effect sizes across the evidence. Aim The purpose of this meta-analysis was to explore the effect of HT on mental health. Methods We used the PRISMA framework. A keyword search of Web of Science, PubMed, ProQuest and Cochrane was performed. The inclusion criteria were HT with RCTs and mental health assessments. A random-effects model was used to perform the meta-analysis. Results A total of 1,056 records were searched, and 18 eligible studies were extracted. The included RCTs had no statistical heterogeneity and publication bias. The meta-analysis showed that the HT experimental groups had a significant and positive impact on mental health compared with the control groups (effect size = 0.55). Discussion HT should be considered for enhancing mental health. The included studies had no negative outcomes and the most common HT intervention was at least eight sessions. Therefore, HT should be considered to enhance mental health. However, the concealed allocation and blinding processes should be improved in future studies. Implications for Practice: This study recommends that HT should be integrated into healthcare settings to improve mental health.