Table 2.
Basic characteristics of the studies included in the review.
| Authors and Year of Publication | Country | Design | Sample | Setting(s) | Intervention | Results |
|---|---|---|---|---|---|---|
| A. Hassan et al., (2020) [39] |
China | Non-randomized control trials | N = 50 (No gender information) Mean age: 20.3, SD = 16.3 Chinese students from the campus of Sichuan Agricultural University |
Greenery included: Indoor with ornamental plants (experimental) No greenery: Indoor without ornamental plants (control) |
5 min of viewing | The STAI scores were lower in the presence of plants, and there was no significant difference between blood pressure and pulse rate. Observation of plants in the work environment enhanced brain wave activity and decreased anxiety to reduce mental stress. |
| Bin Jiang et al., (2014) [5] |
USA | Randomized controlled trials | N = 158 (80 males and 78 females) Mean age: 21.2, SD = 2.7 Healthy Adults |
Video of 10 neighborhood street scenes with different vegetation densities | Watch the 6-min video | There were significant differences between males and females: tree cover at different densities was not associated with pressure recovery for females. For males, pressure recovery increased at 1.7–24%, no change at 24–34%, and slower recovery above 34% (inverted U-shape). Moderate tree density caused greater pressure reduction. |
| Cammie K. Coleman and Richard H. Mattson (1995) [43] |
USA | Non-randomized control trials | N = 50 (No gender information) Age: 18–34 (No average age information) College Students |
Greenery included: A green plant in the room or a life-size color photo of that plant (experimental) No greenery: A metal stool in the room (control) |
Participated in 20-min sessions twice a week for 6 weeks. | Live plants and photographs had a positive response for 38% of participants. 23% had reduced stress in the control group. No significant differences were found for the rest. |
| H. Ikei et al., (2014) [40] |
Japan | Randomized controlled trials | N = 85 (41 males and 44 females) Mean age: 16, SD = 0.9 High school students |
Greenery included: Exposed to foliage plants (experimental) No greenery: No foliage plants (control) |
Ornamental plants for 3 min | Foliage plants resulted in a significant increase in parasympathetic (high-frequency component) activity, suppression of sympathetic (low-frequency component) activity, and a significant decrease in pulse rate. More comfort and relaxation after seeing the plants. |
| Hassan, Ahmad, et al., (2018) [47] |
China | Non-randomized control trials | N = 50 (No gender information) Mean age: 19.6, SD = 1.42 College students experiencing high academic stress |
Greenery included: Indoor plant transplantation (experimental) No greenery: Playing mobile app games (control) |
15 min plant transplanting work | Blood pressure decreased significantly. No change in pulse rate. STAI decreased significantly. SDM felt more relaxed. Alpha and beta wave averages increased over time during the transplantation task. The results of the study suggest that contact with plants minimizes mental stress. |
| Jiang S. et al., (2021) [45] |
China | Randomized controlled trials | N = 50 (all females) Mean age: 22.32, SD = 2.56 Female college students |
Scented primroses (experimental) Unscented primroses (control) |
Exposure to plant environment for 10 min | Mean blood pressure and pulse rate in both conditions decreased significantly after the experiment, and the mean EEG was higher. Both groups of primroses were psychologically and physiologically beneficial. Fragrant primroses caused better effects. |
| Ji-Young Choi et al., (2016) [50] |
Korea | Randomized controlled trials | N = 103 (51 males and 52 females) Mean age: 21, SD = 2.3 College students |
Green indices for indoor spaces were 5%, 20%, 50%, and 80% | Showing green for 3 min | There were no significant differences in physiological parameters with respect to the green index. Significant physiological and psychological improvements. Subjectively, participants preferred 50% of the green index the most. |
| Johan Ottosson and Patrik Grahn (2005) [38] |
Sweden | Randomized controlled trials | N = 15 (2 males and 13 females) Mean age: 86 Elderly people living in homes for the elderly. |
Greenery included: Elderly home garden (experimental) No greenery: Elderly home indoor (control) |
Outdoor leisure activities 1 h | Did not show any effect on blood pressure or heart rate. However, there was a restoration of attention in the elderly. |
| K. Dijkstra et al., (2008) [36] |
Netherlands | Randomized controlled trials | N = 77 (35 males and 42 females) Mean age: 21, SD = 2.2; Students, no details |
Greenery included: With plant ward photo (experimental) No greenery: Without plant ward photo (control) |
View photos of hospital rooms (exact time unknown) | Participants in the ward with indoor plants felt less self-reported stress than those in the ward with paintings. Indoor plants reduced stress by increasing the attractiveness of the room. |
| Kate E. Lee et al., (2015) [35] |
Australia | Randomized controlled trials | N = 150 (71% females) Mean age: 20 Volunteers were recruited from the University Psychology Research Experience Program and the broader student population. |
Greenery included: Green roof simulation view (experimental) No greenery: Urban scenario with a concrete roof (control) |
View 40 s | Changes in subcortical arousal and cortical attentional control occur. Attention is restored, and subsequent benefits may include improved performance and mood, as well as reduced stress. |
| Katinka H. Evensen1 et al., (2013) [42] |
Norway | Randomized controlled trials | N = 85 (28 males and 57 females) Mean age: 24.9, SD = 5.7 College students |
Greenery included: Room with plants with windows (experimental); room with plants without windows (experimental) No greenery: Rooms with computers only (control) |
Oriented attention for 10 min | There was no significant restorative effect of plants. Visual richness in the environment may be a restorative factor. The presence of indoor plants led to higher levels of perceptual fascination with the environment. |
| Ke-Tsung Han (2008) [43] |
China | Non-randomized control trials | N = 76 (58 males and 18 females) Mean age: 13.6 (experimental group); 13.5 (control group) Two classes of students in the second year of junior high school |
Greenery included: Cinnamomum kotoense in the classroom (experimental) No greenery: No plants in the classroom (control) |
Exposure to plant environment for 2.5 months | There was an immediate stronger sense of preference, comfort, and friendliness in the experimental group compared to the control group. STAI, RCS, and RS increased over time, and WBM decreased over time, with improvements over time but not statistically significant. |
| Lee, MS (Lee, Min-sun) et al., (2015) [46] |
Korea | Randomized controlled trials | N = 24 (all males) Mean age: 24.9, SD = 2.1 Young male adults |
Greenery included: Caring for houseplants (experimental) No greenery: Computer tasks (control) |
15 min plant transplanting work | Mean activity of HRV increased over time and decreased at the end of the plant task. Diastolic blood pressure decreased. Positive interaction with houseplants reduces physical and psychological stress. |
| Masahiro Toyoda et al., (2019) [37] |
Japan | Non-randomized control trials | N = 63 (33 males and 30 females) Mean age: 38.7, SD = 9.3(male); 41.6, SD = 9.6 (female) Electricity company employees. |
Greenery included: Small plants on the desk (experimental) No greenery: No plants on the desk (control) |
Observe plants and take care of them for 4 weeks | STAI scores decreased significantly after the intervention period (p < 0.05); pulse rate decreased throughout. Conscious gazing at nearby plants can reduce psychological and physical stress in office workers. |
| Preyen Archary and Andrew Thatcher (2021) [41] |
USA | Randomized controlled trials | N = 60 (21 males and 39 females) Mean age: 21.80, SD = 6.09 Undergraduate students |
Greenery included: Room with two large indoor foliage plants and one small bonsai table plant (experimental) No greenery: Facing the wall with no plants or other irritants (control) |
Facing the plant for 6 min | Distress was significantly reduced, and engagement increased. The presence of indoor plants had a small positive effect on affective recovery and no effect on cognitive recovery. |
| Seong-Hyun Park and Richard H. Mattson (2008) [48] |
USA | Randomized controlled trials | N = 90 (52 males and 38 females) Mean age: 37.6, SD = 9.41 Patients who had undergone an appendectomy |
Greenery included: Ward with foliage and flowering plants, 12 potted foliage and flowering plants (experimental) No greenery: No plants in the ward (control) |
Mean length of stay in wards with plants 4.64 days | Patients had significantly lower postoperative analgesic intake and more positive physiological responses (as evidenced by lower systolic blood pressure and heart rate). Pain, anxiety, and fatigue scores were lower. |
| Seungkeun Yeom et al., (2021) [16] |
Korea | Randomized controlled trials | N = 27 (17 males and 10 females) Mean age: 25.53 (male); 23.15 (female) College students of different majors at Yonsei University |
Greenery included: 8.0 m2 indoor virtual big green wall (experimental); 2.0 m2 indoor virtual small green wall (experimental) No greenery: Blank wall (control) |
Sit in a chair for 5 min and walk around for 1 min | The small green wall had a more dramatic improvement effect. Subjects in the small green wall condition had substantially lower stress levels compared to the non-green wall condition. The large green wall reduced STAI levels but increased mental stress, fatigue, and anxiety. |
| Virginia I. Lohr et al., (1996) [49] |
USA | Non-randomized control trials | N = 96 (48 males and 48 females) Age: 18–46 (No average age information) Predominantly from undergraduate agricultural economics classes |
Greenery included: Computer labs with plants (experimental) No greenery: Computer lab without plants (control) |
Computer tasks completed in indoor spaces with plants | Participants were more productive. Less stressful and more focused. Significant increase in attention span. |
| WeiLin et al., (2019) [12] |
China | Randomized controlled trials | N = 240 (53% females) Mean age: 20.2, SD = 1.76 |
Six different types of small simulated green spaces | Exposure of green space for 10 min | Walking in high PCA (per capita area) and sitting in low PCA have the most powerful effect on reducing stress |
Abbreviations: HRV: Heart Rate Variability; HR: Heart Rate; EEG: Electroencephalogram; EDA: Electrodermal activity; PRS: Perceptual Recovery Scale; STAI: State Trait Anxiety Inventory; DSSQ-S: Dundee Stress State Questionnaire; RCS: Restorative Components Scale; RS: Restorative Scale; TSST: Trier Social Stress Test; POMS: Profile of Mood States; ZIPER: Zuckerman Inventory of Personal Reactions; TMD: Total Mood Disorder; SD: Semantic Differences.