JULY 2010 Issue no.6
The positive effects of office plants
New University of Technology Sydney (UTS) research made possible by nursery levy voluntary contribution funding has found strong evidence supporting the benefits of office plants for reducing stress and negative mood states in office workers. Plants were found to promote wellbeing, and therefore, potentially performance. Staff who had plants placed in their offices showed reductions in stress levels and negative feelings of a magnitude of 30 to 60%, while those with no plants recorded increases in stress and negativity of 20 to 40%, over the 3-month test period. Importantly, just one office plant was enough to make all the difference. In this Nursery Paper, the researchers involved outline their findings.
*The photos featured in this Nursery Paper are all examples of office plants
|*Photo courtesy of Ambius|
The positive effects of office plants
Previous UTS indoor plant research focused on the benefits of pot-plants in reducing urban indoor air pollution1,2, in particular,types of contaminant almost always found in higher concentrations indoors than outside - volatile organic compounds (VOCs) emitting from plastic/synthetic materials (furnishings, furniture, equipment like computers, copiers etc), and CO2 (from occupants breathing). It has been shown that cleaner air leads to better cardiovascular health and clearer thinking3,4. It is also well known that negative mood states can reduce productivity and performance, and stress can lead to serious illness5-9.
This study aimed to examine the extent to which the presence of one or more indoor plants could directly be associated with reductions in stress and negative mood states in office staff.
Previous research has found that indoor plants can result in directly measurable health benefits to building occupants, such as reductions in staff sick leave, possibly over 60%, as well as reduced sick leave absences among school children9. Productivity gains on computer tasks, and reductions in perceptions of pain and discomfort, have also been recorded when plants are present10,11.
Furthermore, beneficial impacts of indoor plants in nursing homes for dementia sufferers have also been reported, including betterstimulated senses and more positive emotional feelings12. A survey with some 450 respondents found that, on all 10 job-satisfaction criteria tested, scores were higher among staff with plants, and that indoor plants were preferred to window views of planted exteriors13.
Four leafy plant treatments were used: 1 or 3 desk plant specimens (200 mm pots) of Spathiphyllum ‘Petite’, or 1 or 2 floor specimens (300 mm pots) of Dracaena ‘Janet Craig’, plus a no-plant control group. After obtaining UTS Human Research Ethics Committee approval, a baseline measure called the Lifestyle Appraisal Questionnaire (LAQ)14 was administered before the plants were installed. The LAQ confirmed that both the male and female staff participants had physical and mental health scores similar to those of the general community over the same age range and sex. Two other internationally validated psychological questionnaire measures were then used to test the effects of plants on negative mood states and levels of stress in participants. Two rounds of each measure were administered, the first before the plants were installed, and the second after they had been in the offices for about three months (one teaching semester).
Of 55 original participants, 40 individuals completed all the psychological measures. This response rate (72%) is scientifically acceptable, with return rates commonly being in the range 18 to 35%15,16. The two selected measures have been used by health professionals for over 30 years to assess mental health status in such states as anxiety, depressive mood, stress, and so on, in a number of clinical and non-clinical situations. The two measures were:
The Profile of Mood States (POMS)17 comprises 65 items that make up six sub-tests, plus a composite total measure. The six sub-categories include five negative states: tension (anxiety), depressive mood, feelings of anger, levels of fatigue, confusion, and one positive state called vigour, plus the composite total. Participants respond on a five-point Likert scale, 0 to 4, with 0- being ‘Not at all like me’, to 4- ‘Extremely like me’, with descriptors such as ‘Friendly’, ‘Hopeless’, ‘Energetic’, ‘Sympathetic’, etc.
The General Health Questionnaire (GHQ)18 assesses recent or current feelings of stress, revealed by responses on such matters as ability to concentrate, sleep, or make decisions. The 30-question version of the test was used here. The survey uses a fourpoint Likert scale: 1- ‘Better than usual’, 2- ‘Same as usual’, 3- ‘Less than usual’, and 4- ‘Much less than usual’, the last two responses indicating increasing feelings of stress, and summed for final scores.
Reductions in POMS scores with plant presence
Changes in mean total scores in the four plant treatments and the control group are shown in Figure 1. All the plant treatments yielded similar positive results. This means that just one plant can make all the difference in raising mood and reducing stress levels. The no-plant control group in contrast scored a 30% increase in overall negative feelings.
Figure 1. Differences in POMS scores in the five treatment groups before and after plant placement. (Code: D1 and D3: 1 or 3 desk plants; F1 and F2: 1 or 2 floor plants; R0: control – no plants. Means ± SE, N = 7-9).
In the six sub-categories (Table 1), plant presence resulted in very large statistically significant reductions in negative mood feelings, of around 30 to 60%, as well as in overall totals, while feelings of vigour (enthusiasm, energy) remained level over the period. However, in the control group, there was a decrease in vigour of nearly 30%, and an increase of over 40% in overall negative feelings. However, with only a small number of control participants in this treatment, the results for this group were not statistically significant below the 5% probability level.
Table 1. Difference in scores for POMS, sub-categories and totals, for participants before and after plant placements, plus no-plant control group. (N with plants = 31; N with no plants = 9)
* Difference statistically significant (p≤0.05)
**Difference highly significant (p≤0.001)
No asterisk – difference not statistically significant.
Figure 2. Differences in total GHQ scores in the treatment groups before and after plant placement. (Code: D1 and D3: 1 or 3 desk plants; F1 and F2: 1 or 2 floor plants; R0: reference/control – no plants. Means ± SE, N = 7-9).
Reductions in GHQ scores with plant presence
Changes in mean total scores for the ‘more stressed’ plus ‘very stressed’ responses among the four individual plant treatments and the no-plant group, are shown in Figure 2, while the overall results for plant presence/ absence are presented in Table 2. The results show similar responses to those found with the POMS questionnaires. Plant presence was again associated with a very significant reduction of 50% in feelings of stress or anxiety. In contrast, the no-plant groups recorded a 20% increase in stress scores over the 3-month period (as would be expected towards the university examination period), but again, because of the small size and variability in the control group, this increase was not statistically significant at p≤0.05).
Table 2. GHQ scores for participants before and after plant placement, plus no-plant control group. (N with plants = 31; N with no plants = 9)
**Difference highly significant (p≤0.001).
No asterisk – difference not statistically significant.
Significance of findings
This is the first study designed to investigate directly the effects of plant presence on negative mood states in building occupants, and the first to utilise internationally validated psychological measures for assessing the potential benefits of indoor plants. The results show that plant presence is associated with large reductions in negative mood states and levels of stress among building occupants. Presumably similar benefits can be predicted for indoor plants placed in the home, in health care facilities, or other building situations. Environmental psychologists consider that close-by living greenery is beneficial because it acts as a restorative environment at a subconscious level. Nearby plants relieve ‘attention fatigue’ and ‘re-set’ a feeling of calm, which reflects our evolutionary history of dependence on plants for shelter and security19.
On a cautionary note, the number of participants completing all questionnaires was relatively small for psychological testing, and a larger survey is needed to confirm and advance further our understanding of indoor plant/ human wellbeing relationships.
Our previous studies1,2 have demonstrated that a couple of pot-plants per office-space can bring significant reductions in indoor VOC levels, and for CO2 reductions, the more foliage the better. We are currently profiling CO2 uptake capacities under various lighting regimes to gain a more detailed understanding of species differences in CO2 uptake performance, but for now, place plants according to their recommended shade tolerances for optimum results.
This study shows that just one plant per workspace can provide a very large lift to staff spirits, and so promote wellbeing and performance.
*Photo courtesy of Ambius
|Cited literature examples|
1) Burchett MD, Torpy F and Brennan J, 2009, Towards Improving Indoor Air Quality With Potted -Plants A Multifactorial Investigation, Final Report to Horticulture Australia Ltd.
2) Burchett MD, Torpy F, Brennan J and Craig A, 2010, Greening the Great Indoors for Human Health and Wellbeing, Final Report to Horticulture Australia Ltd.
3) US EPA, 2000, Healthy Buildings, Healthy People: A Vision For The 21st Century, Office of Air and Radiation. Air: VOCs, 3-6, 29.
4) US EPA, 2003, Indoor Air Quality and Student Performance, Report of Indoor Environments Division, 8 pp.
5) Kopp MS, Stauder A, Purebl G, Janszky I and Skrabski A, 2007, Work stress and mental health in a changing society, The European Journal of Public Health, 18, 3, 238-244.
6) Melchior M, Caspi A, Milne BJ, Danese A, Poulton R and Moffitt T, 2007, Work stress precipitates depression and anxiety in young, working women and men, Psychological Medicine, 37, 8, 1119-1129.
7) Ricci JA, Chee E, Lorandeau AL and Berger J, 2007, Fatigue in the U.S. Workforce: prevalence and implications for lost productive work time, Journal of Occupational and Environmental Medicine, 49, 1, 1-10.
8) Wang PS, Simon GE, Avorn J, Azocar F, Ludman EJ, McCulloch J, Petukhova MZ and Kessler RC, 2007, Telephone screening, outreach, and care management for depressed workers and impact on clinical and work productivity outcomes, Journal of the American Medical Association, 298, 1401-1411.
9) Fjeld T, 2002, The effects of plants and artificial daylight on the well-being and health of office workers, school children and health-care personnel, Proceedings of International Plants for People Symposium, Floriade, Amsterdam, NL.
10) Lohr VI, Pearson-Mims CH and Goodwin GK, 1996b, Interior plants may improve worker productivity and reduce stress in a windowless environment, Environmental Horticulture, 14:2, 97-100.
11) Lohr VI and Pearson-Mims CH, 2000, Physical discomfort may be reduced in the presence of interior plants, HortTechnology 10:1, 53-58.
12) Rappe E & Lindén L, 2002, Plants in health care environments: experiences of the nursing personnel in homes for people with dementia, Acta Horticulturae 639: XXVI International Horticultural Congress: Expanding Roles for Horticulture in Improving Human Well-Being.
13) Dravigne A, Waliczek TM, Lineberger RD, Zaljicek JM, 2008, The effect of live plants and window views of green spaces on employee perceptions of job satisfaction, Hortscience 43, 1, 183-187.
14) Craig A, Hancock K and Craig M, 1996, The lifestyle appraisal questionnaire: a comprehensive assessment of health and stress, Psychology and Health, 11, 331-343.
15) Edwards P, Roberts I, Clarke M, DiGuiseppi C, Pratap S, Wentz R and Kwan I, 2002, Increasing response rates to postal questionnaires: systematic review, British Medical Journal, 324 (7347), 1183.
16) Yu J and Cooper H, 1983, A quantitative review of research design effects on response rates to questionnaires, Journal of Marketing Research, 20, 1, 36-44.
17) Craig A, Tran Y, Lovas J and Middleton J, 2008, Spinal cord injury and its association with negative psychological states, International Journal of Psychological Rehabilitation, 12, 2, 115-121.
18) Dale B, Sævareid HI and Söderhamn O, 2009, Testing and using Goldberg’s General Health Questionnaire: Mental health in relation to home nursing, home help, and family care among older, care-dependent individuals, International Journal of Mental Health Nursing,18 , 2, 133 – 143.
19) Kaplan S, 1995, The restorative benefits of nature: towards an integrative framework, Journal of Environmental Psychology, 15, 169-182.
This Nursery Paper was written by Prof A. Craiga, Dr F. Torpyb, J Brennanb & Prof MD Burchettb.
a. Northern Clinical School, Fac. Med., Univ. Syd.
b. Plants and Indoor Environmental Quality Group, Centre for Environmental Sustainability, Fac. Sci., Univ. of Technology, Sydney (UTS) The authors thank the National Interior Plantscape Association, Nursery & Garden
Industry Australia and Horticulture Australia Ltd for their research funding support for this project. Thanks also to Ambius for funding support for UTS indoor plant research, and to numerous colleagues in the Faculty of Science and Faculty of Design, Architecture and Building, for their interest, assistance and participation in this project.
|Compiled and edited by Sarah McMahon, NGIA Communications & PR Coordinator; banner photography by Anthony Tesselaar.|
© NGIA Ltd 2010. While every effort is made to ensure the accuracy of contents, Nursery & Garden Industry Australia Ltd accepts no liability for the information. Published by NGIA, PO Box 907 EPPING NSW 1710.
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