Table 1.

Evidence summary: randomised controlled trials

Author, date and country	Study aims	Garden type	Age	Outcomes measured	Key findings	Author conclusions
Christian et al, UK 31	To evaluate the impact of a school gardening programme, the Royal Horticultural Society (RHS) Campaign for School Gardening, on children’s fruit and vegetable intake	School gardening	8–11 years	Change in fruit and vegetable intake. Child-level data—school food diary, home food diary—Child and Diet Evaluation Tool (CADET), knowledge and attitude questionnaire. School level—school gardening level questionnaire, gardening in schools—process measures email, information collected from RHS advisor on school gardening in intervention schools. Outcomes measured at baseline (May/June 2010) and October 2011 to January 2012	Trial 1: Higher mean change of 8 g (95% CI –19 to 36) for combined fruit and vegetable intake for teacher-led group than for RHS-led group –32 g (95% CI –60 to –3), difference not significant (intervention effect –43 g, 95% CI –88 to 1, p=0.06). Trial 2: More fruit and vegetables consumed in teacher-led group (15 g (95% CI –36 to 148), difference not significant. Schools which improved their RHS gardening score by three levels, on average, an increase in intake of fruit and vegetables by 81 g (95% CI 0 to 163, p=0.05) compared with children attending schools that had no change in gardening score	There is little evidence that school gardening alone can improve children’s fruit and vegetable intake. When gardening was implemented at the highest intensities the findings suggest it could improve children’s fruit and vegetable intake by a portion per day
Detweiler et al, USA 35	To assess the effect of horticultural therapy on cortisol levels, depression, symptoms of post-traumatic stress disorder, alcohol cravings, and quality of life symptoms compared with a non-horticultural OT group.	Structured gardening programme	Mean age 46.4 years (SD=11.9)	Quality of life (Quality of Life Enjoyment and Satisfaction Questionnaire - Short Form (Q-LES-Q-SF)), alcohol craving (Alcohol Craving Questionnaire (ACQ-NOW), PTSD (Posttraumatic Stress Disorder Checklist Civilian Version (PCLC)), depression (Centre for Epidemiologic Studies Depression Scale (CES-D)), outcomes assessed pretreatment and post-treatment. Salivary cortisol samples were taken at weeks 1, 2, and 3	24 participants completed protocol. Although a positive impact of HT was seen in a 12% reduction in salivary cortisol levels from week 1 to week 3, the difference was not statistically significant (analysis of variance (ANOVA) (F2, 20=0.878), p=0.43). Separate one-way analyses of covariance (ANCOVAs) found no statistically significant differences in the self-administered tests. A positive trend was seen in improving quality of life and depressive symptoms in the HT group (Q-LES-Q-SF, p=0.001 and CES-D, p<0.001) compared with the OT group (Q-LES-Q-SF, p=0.029 and CES-D, p=0.050). HT group did not significantly improve in ACQ-NOW (p=0.118), whereas the OT group did (p=0.040). HT group did significantly improve in PCLC (p=0.039), whereas the OT group did (p=0.135)	HT may have a role in reducing stress and depression and quality of life more than the programmes in which the OT participated
Jarrott et al, USA 56	To compare a randomly assigned treatment group, that received horticultural therapy-based programming to a comparison group, that engaged in traditional activities programming, on engagement and affect	HT**	Mean age of 80.09 years (SD=8.05)	Level of cognitive impairment (Mini-Mental Status Exam) Affect (Apparent Affect Rating Scale) Engagement (Menorah Park Engagement Scale) Observations took place twice a week during weeks 1, 2, 5 and 6	No significant differences between groups were found on affect (pleasure (z=−1.544, p=0.123), anxiety (z=−0.086, p=0.932) and interest (z=−1.26, p=0.208)). Levels of adaptive behaviour differed between the groups, with the treatment group demonstrating higher levels of active (z=−2.90, p=0.00), passive (z=−2.72, p=0.01) and other engagement (z=−3.47, p=0.00) and the comparison group demonstrating higher levels of self-engagement (z=−4.60, p=0.00)	HT-based activities successfully facilitate lower levels of self-engaging behaviours and engage groups of dementia sufferers who are often difficult to engage in activities that elicit high levels of adaptive behaviour
Van den Berg et al, The Netherlands 96	To hypothesise and test the stress-relieving effects of gardening	Gardening	Mean age 57.6 years (range 38–79)	Stress—salivary cortisol levels and self-reported mood (Positive and Negative Affect Schedule (PANAS)), saliva samples collected shortly after arrival at the experimental location, before/after the stressful task, halfway through and after experimental activity. PANAS assessed prior to/after stressor and after experimental activity	Study findings suggest that gardening has a positive impact on relief from acute stress. Both gardening and reading decreased cortisol levels during the recovery period, with significantly stronger decreases seen in the gardening group ((F (1, 11)=24.15, p<0.001 vs. F (1, 13)=5.33, p<0.05). Postactivity, cortisol levels were marginally lower in the gardening group than in the reading group (F (1, 27)=3.21, p=0.08). A significant increase in positive mood was seen in the gardening group (F (1, 12)=4.91, p<0.05), but deteriorated by 4.3% in the reading group (p=0.53). Postactivity positive mood was significantly higher in the gardening group than in the reading group (F (1, 28)=4.93, p<0.05).	Gardening can promote relief from acute stress. Gardens can be used as a valuable resource to prevent disease and promote health
Gatto et al, USA 43	To explore the effects of a novel 12-week gardening, nutrition and cooking intervention ('LA Sprouts') on dietary intake, obesity parameters and metabolic disease risk among low-income, primarily Hispanic/Latino youth in Los Angeles	Structured gardening programme	Third, fourth and fifth grade students (age range 8–11 years)	Dietary intake measured via food frequency questionnaire, anthropometric measures (body mass index, waist circumference), body fat and fasting blood samples	Study findings indicate that pupils participating in LA sprouts had significant reductions in body mass index z -scores as compared with the controls (−0.1 vs −0.04, p=0.01). Waist circumference in the LA Sprouts group decreased more than the control (−1.2 vs 0.1 cm: p<0.001). Dietary fibre increased with LA sprouts as compared with the controls (+3.4% vs −16.5%; p=0.04), however there was no difference in the fruit intake between the LA Sprouts and control groups	The findings are positive and indicate that LA Sprouts can benefit pupils’ nutritional behaviours and impact on body mass index and waist circumference, but larger, longitudinal studies are required
Kam et al, China110	To examine HT activity on reduced stress, improved quality of life and work performance for people with psychiatric disorders	HT**	Mean age of 44.3 years (SD=11.6)	Well-being and quality of life (Personal Well-being Index (PWI-C)), mental state and behaviour (Depression Anxiety Stress Scale (DASS-21)), general functioning (Work Behaviour Assessment (WBA)), PWI-C and DASS-21 measured before and after intervention	A significant positive impact of the horticultural programme was seen in DASS-21 total (p=0.01), depression (p=0.04), anxiety (p=0.01) and stress (p=0.5) subscales. No significant differences were seen in change of WBA and its subscales (p values range from 0.08 to 0.79) and PWI (p=0.84). Qualitative evidence suggested a positive impact on emotional, occupational, social and spiritual aspects	HT is effective in reducing anxiety, depression and stress but no difference was seen on work behaviour or quality of life
Bail et al (2018) UK28	To assess a mentor home-based vegetable garden as an intervention to cancer survivors to explicate health-related outcomes	Gardening programme	Adults—all ages, mean age of 60 years	Health-related outcomes (secondary outcomes of vegetable consumption, physical activity, performance and function, HRQOL, anthropometrics and biomarkers) veg consumption, physical activity, HRQOL, Physical Performance, Anthropometrics, biomarkers such as toenail clippings to measure chronic stress levels	100% satisfaction with the programme. Statistically significant improvements with physical activities and vegetable consumption. Positive changes reported in the HRQOL scores. Non-significant trends noted in the body mass index recordings. Overall, positive changes were reported across both groups, with a marked improvement in the intervention groups scores compared with the controls.	Home-based mentoring gardening programme can significantly improve biometric outcomes and vegetable consumption
Lai et al, China 65	To explicate the impact of HT on frail older nursing home residents on psychological well-being	HT**	Frail older adult and prefrail	Happiness was measured using the subjective happiness scale; frailty was measured using the five-item Fried Frailty Index; depressive symptoms were measured using the Geriatric Depression Scale; self-efficacy was measured using the 10-item General Self-Efficacy Scale; social engagement measured using the Social Engagement Scale; social networks were measured using Lubbens Social Network Scale and well-being was measured using the Personal Well-being Index	Significant improvement in the interaction time was observed in the happiness scale in the HT groups (β=1.457, p=0.036). No significant changes noted in any of the other outcomes. A later cluster analysis (follow-up) indicated greater effects on subjective happiness for the HT group (mean difference=6.23, p<0.001) as compared with the controls at baseline	Frail and prefrail older people living in a nursing home can benefit from HT and can promote subjective happiness

HT**, horticultural therapy.