Note: the following article was originally written in French, and can be viewed in French here
In the case of a non-pharmacological intervention such as horticultural therapy, it is useful to establish whether it brings benefits to people in a variety of situations linked to mental health or neurodegenerative diseases, rehabilitation following a stroke or accident, post-traumatic stress, and others. In addition, research can attempt to explain how the intervention works, and what mechanisms come into play.
This is a huge undertaking, to say the least. Its aim is to better understand horticultural therapy in order to implement it more effectively and to contribute to its development. Ideally, good-quality studies should help practitioners in the field, but also facilitate the adoption of horticultural therapy by providing the arguments needed to convince decision-makers including health institutions, doctors, and department heads.
This model is inspired by Evidence-Based Medicine, which holds that it is by combining clinical observation with the results of the most recent and conclusive research that we obtain the most appropriate solution for the patient or the person receiving care. The same principles underpin Evidence-Based Design, of which Roger Ulrich is the most frequently cited researcher, i.e. the design of healthcare facilities based on research data and evidence.
Not all studies are created equal
However, it is impossible to apply the same methodologies used in medical research to the study of horticultural therapy. For example, it is not possible to use a double-blind design to study an HT activity where neither the caregiver nor the participant knows whether the horticultural therapy is being applied or not! Even so, the aim is to develop methodologies that are as rigorous as possible, to ensure that the study observes what it set out to observe, by “controlling” the variables as much as possible. But not all studies are equal in quality and power. Sometimes, for a variety of reasons, the quality is not up to scratch. This is what this Cochrane review of studies on horticultural therapy and schizophrenia points out (for more info on Cochrane reviews). Research is important. But good research, whether quantitative or qualitative, is even better.
How can you find relevant studies?
The good news is that you no longer need access to a university library to find studies published in scientific journals. Thanks to Google Scholar, ResearchGate, and other search tools, you can identify studies that will help you set up a therapeutic garden project or do the literature review you need before launching…a new study. In 10 years, the number of publications has risen sharply (15,600 results for “horticultural therapy research” in the period 2010-2020 versus 6,400 for 2000-2010). The elderly and people suffering from mental disorders have received the most attention. At present, Korea, China, Japan, and Singapore seem to be producing the most research in the field.
10 years, 10 studies
Here is a random selection of 10 studies, literature reviews or meta-analyses published over the last 10 years. I’ve tried to pick a variety of subjects. Another criterion was to make sure the entire article was available online free of charge. For each study, here is the abstract or conclusion and the link to the full article.
Reduction of post-traumatic stress and depression for natural disaster survivors (Japan)
Kotozaki, Y. (2013). The psychological changes of horticultural therapy intervention for elderly women of earthquake-related areas. Journal of Trauma Treat, 3(1), 1-6.
“Despite the passage of time, some people who experienced the Great East Japan Earthquake are still living with the emotional trauma and stress. We provided horticultural therapy as an intervention to 39 elderly women with earthquake stress living in the affected areas of coastal areas of the Great East Japan Earthquake. The participants were divided into two groups, an intervention group (n=20) and a control group (n=19). The intervention group underwent eight weeks of horticultural intervention. On the other hand, the control group underwent eight weeks of stress control education. After two months of horticultural therapy intervention, the Clinician-Administered PTSD Scale (CAPS) total score, the Geriatric Depression Scale (GDS) score, the Posttraumatic Growth Inventory (PTGI-J) score, and the WHO Quality of Life 26 (WHO-QOL26) score in the intervention group improved significantly, and salivary cortisol level in the intervention group also improved significantly. After follow-up, CAPS score, GDS score, PTGI-J score, and WHO-QOL26 score (psychological QOL score, social QOL score, environmental QOL score, and global QOL score), and salivary cortisol level in the intervention group was improved or almost the same as the post-intervention scores in the intervention group. These findings suggest that horticultural therapy has an effect on the symptoms of earthquake stress in elderly women and that this effect may sustain.”
A literature review about garden design for cognitively-impaired elderly people (France)
Charras, K., Laulier, V., Varcin, A., & Aquino, J. P. (2017). Conception de jardins à l’usage des personnes âgées atteintes de troubles cognitifs: revue de la littérature et cadre conceptuel fondé sur la preuve. Gériatrie et Psychologie Neuropsychiatrie du Vieillissement, 15(4), 417-424.
“The use of gardens as a place of conviviality, activity and resourcing is becoming increasingly popular in social and medico-social establishments for elderly people with cognitive disorders. However, scientific publications on the benefits of gardens for the cognitively impaired elderly are rare. The aim of this literature review is to identify the main scientific data relating to the design, use and therapeutic benefits of gardens for people with Alzheimer’s. Using components drawn from the main models of therapeutic garden design, an evidence-based design approach was adopted to determine the impact on the well-being and behaviour of sufferers. Twenty-two articles were selected for this study, with a low level of evidence by scientific standards. The results of this literature review highlight six dimensions of landscape design. These six dimensions are grouped into a conceptual framework and discussed in terms of landscape design and its impact on people with Alzheimer’s disease.”
Meta-analysis on cognitive improvement (Taiwan)
Tu, H. M., & Chiu, P. Y. (2020). Meta-analysis of controlled trials testing horticultural therapy for the improvement of cognitive function. Scientific reports, 10(1), 1-10.
“Improving cognitive function is one of the most challenging global issues in cognitive impairment population. Horticultural therapy involves the expertise of a horticultural therapist who establishes a treatment plan for horticultural activities that aim to achieve cognitive changes, and thereby improve health-related quality of life. However, more convincing evidence demonstrating the effect of horticultural therapy on cognitive function is essential. The purpose of this study was to conduct a meta-analysis of controlled trials testing the effect of horticultural therapy on cognitive function and the findings indicate that horticultural therapy programs significantly improved cognitive function. The effect size of the horticultural therapy program was large. The findings of this meta-analysis have important implications for practice and policies. Contemporary healthcare systems should consider horticultural therapy as an important intervention for improving patients’ cognitive function. Governments and policy-makers should consider horticultural therapy as an important tool to prevent the decline of cognitive function in cognitive impairment population.”
Horticultural activity in elementary school and stress reduction (China, Egypt)
Shao, Y., Elsadek, M., & Liu, B. (2020). Horticultural activity: Its contribution to stress recovery and wellbeing for children. International Journal of Environmental Research and Public Health, 17(4), 1229.
“In recent years, children’s use of mobile phones has grown rapidly, which might lead to an increase in mental stress and negatively affect their health. Despite increasing evidence that horticultural activity can provide significant health benefits, few scientific evidence-based studies are currently available regarding these benefits to children’s health and well-being in schools. Therefore, this study aims to determine the potential benefits of horticultural activity for children from both psychological and physiological perspectives. Twenty-six elementary school students (mean age, 8.12 ± 0.21 years) were asked to perform a plant-related task and a mobile game task for 5 min. During both tasks, physiological sensors were used to measure the participant’s heart rate variability, skin conductance, and skin temperature. Additionally, the participants’ emotional responses were assessed using semantic differential and State–Trait Anxiety Inventory tests immediately after each task. Results revealed that, compared with the mobile game task, participants’ health statuses were positively correlated with the horticultural task, including a considerable decrease in skin conductance and sympathetic nervous activity, together with a marginal increase in parasympathetic nervous activity. Such responses suggested that horticultural activity increased relaxation and decreased feelings of stress. Furthermore, the horticultural activity was associated with a substantial increment in comfort, naturalness, relaxation, and cheerfulness feelings, as well as a significant reduction in depression and a reduction in total anxiety levels. Given these positive benefits, horticultural activity may provide a great contribution to children’s healthy life at school, prompt psychological relaxation, and minimize mental stress relative to smartphone games.”
Horticultural therapy and suicidal risk reduction in veterans (United States)
Meore, A., Sun, S., Byma, L., Alter, S., Vitale, A., Podolak, E., … & Haghighi, F. (2021). Pilot evaluation of horticultural therapy in improving overall wellness in veterans with history of suicidality. Complementary therapies in medicine, 59, 102728.
“Novel approaches to mental health and suicide prevention are lacking. Converging evidence has shown the effectiveness of horticultural therapy (HT) in improving mental health symptoms, but whether it would reduce suicide risk and contributing risk factors is unknown.
Using a cohort model, HT was delivered 3.5 h over four weekly, sessions administered by a registered horticultural therapist to veterans with history of suicide ideation or attempt who felt isolated and experienced ongoing environmental stressors with interest in learning new coping strategies.
HT delivery occurred in an urban garden, through a community partnership between the VA (Veterans Administration) and the New York Botanical Garden. Guided by principles of biophilia, participating veterans took part in nature walks, self-reflection and journaling, and planting activities.
Stress, mood, pain, and social isolation levels were measured weekly pre-post HT sessions using thermometer scales, with concordant validity to validated clinical instruments.
Of the 20 men and women with a history of suicide attempts/ideation, HT demonstrated immediate improvements after each session across all symptom domains in magnitude of reduction in stress, pain, mood, and loneliness. The effect sizes were in medium to large range (Cohen’s d>.5). Additionally, a single HT session showed a sustained effect over subsequent 2-to-4 weeks as observed by the significantly decreased pre-session thermometer scores in subsequent weeks. Reductions in mood symptoms correlated with decline in suicidal ideation (rs = 0.63).
HT intervention maybe a promising therapeutic modality for improving overall wellness in suicide prevention in at-risk veteran populations.”
A program of Therapeutic Patient Education combining garden and art therapy for obese patients (Switzerland)
Sittarame, F., Lanier-Pazziani, M., Chambouleyron, M., & Golay, A. (2021). ETP/TPE (Educ Ther Patient/Ther Patient Educ), 13, 10203.
“Therapeutic education programs for obese patients, including art therapy and therapeutic gardens, profoundly mobilize the interiority of obese people. They help improve quality of life and self-esteem. Objectives: The aim of this study was to evaluate a therapeutic education program combining garden and art therapy offered to groups of obese patients. Method: 12 “garden and art therapy” sessions were offered to 12 obese patients over the course of a year. Following the cycle of the seasons, various themes related to the experience of patients suffering from obesity were treated. A two-hour focus group with the participants at the end of the program was used to evaluate the process. Results: Adherence to the program was 85%. Patient feedback gathered during the focus group was divided into 7 categories: nature as a resource, the sensory garden, the garden as a mediator for getting in touch with oneself, the garden as a source of metaphors for self-expression, creative art therapy, the influence of the group and a different approach to care. Conclusion: The association of garden work and art therapy in a therapeutic patient education program seems to be relevant and could be transposable to other chronic illnesses.”
Beyond horticultural therapy, nature-based interventions (United Kingdom)
Coventry, P. A., Brown, J. E., Pervin, J., Brabyn, S., Pateman, R., Breedvelt, J., … & White, P. L. (2021). Nature-based outdoor activities for mental and physical health: Systematic review and meta-analysis. SSM-population health, 16, 100934.
“Mental health problems are associated with lower quality of life, increased unscheduled care, high economic and social cost, and increased mortality. Nature-based interventions (NBIs) that support people to engage with nature in a structured way are asset-based solutions to improve mental health for community based adults. However, it is unclear which NBIs are most effective, or what format and dose is most efficacious. We systematically reviewed the controlled and uncontrolled evidence for outdoor NBIs. The protocol was registered at PROSPERO (CRD42020163103). Studies that included adults (aged ≥18 years) in community-based settings with or without mental and/or physical health problems were eligible for inclusion. Eligible interventions were structured outdoor activities in green and/or blue space for health and wellbeing. We searched ASSIA, CENTRAL, Embase, Greenfile, MEDLINE, PsycINFO, and Web of Science in October 2019; the search was updated in September 2020. We screened 14,321 records and included 50 studies. Sixteen studies were randomised controlled trials (RCTs); 18 were controlled studies; and 16 were uncontrolled before and after studies. Risk of bias for RCTs was low to moderate; and moderate to high for controlled and uncontrolled studies. Random effects meta-analysis of RCTs showed that NBIs were effective for improving depressive mood −0.64 (95% CI: 1.05 to −0.23), reducing anxiety −0.94 (95% CI: 0.94 to −0.01), improving positive affect 0.95 (95% CI: 0.59 to 1.31), and reducing negative affect −0.52 (95% CI: 0.77 to −0.26). Results from controlled and uncontrolled studies largely reflected findings from RCTs. There was less evidence that NBIs improved physical health. The most effective interventions were offered for between 8 and 12 weeks, and the optimal dose ranged from 20 to 90 min. NBIs, specifically gardening, green exercise and nature-based therapy, are effective for improving mental health outcomes in adults, including those with pre-existing mental health problems.”
Horticultural therapy and general health in the elderly (China)
Wang, Z., Zhang, Y., Lu, S., Tan, L., Guo, W., Lown, M., … & Liu, J. (2022). Horticultural therapy for general health in the older adults: A systematic review and meta-analysis. PloS one, 17(2), e0263598.
With a pronounced and historically unprecedented tendency of population ageing, research on ageing and related disorders has been increasingly brought into focus. Horticultural therapy (HT), as an important role of social prescribing, has been an integrative for decades. This systematic review and meta-analysis aimed to evaluate HT for general health in older adults.
Electronic databases including PubMed, Web of Science, ScienceDirect, the Cochrane Library, MEDLINE (Ovid), EMBASE (Ovid), CINAHL (EBSCO), China National Knowledge Infrastructure (CNKI), and the Wanfang database, grey literature databases and clinical trials registers were searched from inception to March 2021. Randomized controlled trials (RCTs), quasi-RCTs (QRCTs) and the cohort studies about HT for adults aged over 60 were included in this study. Outcome measures were physical function, quality of life, BMI, mood tested by self-reported questionnaire and the expression of the immune cells. The study was registered under PROSPERO (CRD42019146184).
Totally, fifteen studies (thirteen RCTs and two cohort studies) involving 1046 older participants were included. Meta-analysis showed that HT resulted in better quality of life (MD 2.09, 95% CI [1.33, 2.85], P<0. 01) and physical function (SMD 0.82, 95% [0.36, 1.29], P<0.01) compared with no-gardener; the similar findings showed in BMI (SMD -0.30, 95% [-0.57, -0.04], P = 0.02) and mood tested by self-reported questionnaire (SMD 2.80, 95% CI [1.82, 3.79], P<0. 01). And HT might be conducive on blood pressure and immunity, while all the evidence were moderate-quality judged by GRADE.
HT may improve physical function and quality of life in older adults, reduce BMI and enhance positive mood. A suitable duration of HT may be between 60 to 120 minutes per week lasting 1.5 to 12 months. However, it remains unclear as to what constitutes an optimal recommendation.”
Horticultural therapy, anxiety, and depression (United States)
Lasater, Claudia Andrea (2022). “A Systematic Review of Studies Evaluating the Effectiveness of Horticultural Therapy for Increasing Well-Being and Decreasing Anxiety and Depression”. Digital Commons @ ACU, Electronic Theses and Dissertations. Paper 470.
“Table 4 presents information about each of the studies included in the meta-analysis. As the table shows, there was considerable variation among the included studies. Treatment populations studied included Korean white-collar workers (Cha & Lee, 2018); Hong Kong adults with severe mental illness (Kam & Siu, 2010); South Korean, middle-aged, post-menopausal women (Kim & Park, 2018), caregivers of elderly persons with dementia (Kim et al., 2020), elderly people with memory problems and depressive symptoms (Makizako et al., 2019), elderly Asians with no history of severe medical or psychiatric diagnoses (Ng et al., 2018); recovering Swedish stroke patients (Pálsdóttir et al., 2020); people with mental illness (Siu et al., 2020), elderly nursing home residents (Tse, 2008); Serbian psychiatric patients (Vujcic et al., 2017); and 60- year-old people diagnosed with Alzheimer’s-type dementia and apathy (Yang et al., 2021).
While all of the included studies used some type of horticultural component, interventions varied. In some cases, a trained horticultural therapist conducted the intervention, while other studies made no mention of therapist training. Some studies used a horticultural activity as a component of a larger intervention (e.g., Kam & Siu, 2010), while other studies used a well-defined horticultural therapy activity. However, a lack of standardization of the horticultural therapy intervention was apparent across all of these studies. The number of sessions varied from as few as eight sessions to as many as 30 to 20 sessions. Session length also varied from one-hour sessions to 3.5-hour sessions. Most of the interventions were conducted weekly; some occurred twice per week; and in one study, the intervention was carried out 10 times within two weeks (Kam & Siu, 2010).
Variation also existed in the type of control condition used with several studies using a standard care treatment as a comparison group, and other studies using a no treatment group as a control group. As the table indicates, variation also existed in outcome measures used. In all cases, the overall study quality rating was moderately high. The quality rating scores ranged from 62 to 76 on a 90-point scale.
By entering the data obtained from the Comprehensive Meta-Analysis V 2 software for analysis, three outcome variables were analyzed. To generate Forest and Funnel plots, R (version 4.0.4) (R Core Team, 2020) with the metafor package (version 3.0.2) (Viechtbauer, 2010) was used. Figure 2 demonstrates a meta-analysis of treatment vs. control studies using well-being as an outcome variable. The following five articles show an overall fixed effect of 0.54 for well-being which shows that horticultural therapy and related interventions have an effect on well-being.”
Children and healing gardens (United Kingdom)
Din, S. K. J., Russo, A., & Liversedge, J. (2023). Designing Healing Environments: A Literature Review on the Benefits of Healing Gardens for Children in Healthcare Facilities and the Urgent Need for Policy Implementation. Land, 12(5), 971.
“Despite the well-known benefits of healing gardens for children in healthcare facilities, policies and guidelines for their implementation are lacking, leading to their undervaluation by policymakers. This literature review investigates the advantages of healing gardens for children’s health and wellbeing, with a focus on public-funded healthcare facilities. The review explores the definition of a healing garden, theories, the value of play, the impact on children’s development, and the environmental benefits of healing gardens. Additionally, the review presents successful examples of healing gardens in practice, while acknowledging potential arguments against them and associated risks. During the literature review, research gaps were identified, and areas for future research were also examined. Finally, this review calls for evidence-based guidelines for policymakers and designers to incorporate healing gardens into healthcare facilities, providing a comprehensive argument for their adoption and regular access for children.”