A number of studies have investigated the effects of indoor plants on outcomes relevant to the effectiveness and well-being of office workers. Those outcomes include psychophysiological stress responses, task performance, emotional states, and room assessments (Adachi et al., 2000; Chang and Chen, 2005; Coleman and Mattson, 1995; Kim and Mattson, 2002; Larsen et al., 1998; Liu et al., 2003; Lohr et al., 1996; Shibata and Suzuki, 2001, 2002, 2004). In addition, some studies have investigated attitudes toward plants in the workplace (Shoemaker et al., 1992), and the effects of indoor plants on health and discomfort symptoms related to the sick building syndrome (Fjeld, 2000; Fjeld et al., 1998, 1999).
With the exception of four field studies (Fjeld, 2000; Fjeld et al., 1998, 1999; Shoemaker et al., 1992), the previous studies on the psychological benefits of indoor plants have been experiments conducted in laboratories or simulated settings. Laboratory experiments offer important advantages for making claims about causality. These include control over the environment, control for self-selection of different people into different experimental conditions, and precise measurement of performance on standardized tasks. However, their artificiality and brief duration can elicit behavior unrepresentative of what occurs in an actual workplace (Sundstrom, 1986). The results from studies conducted in either laboratories or simulated settings might not generalize well to real workplace settings.
Part of the challenge in generalizing from laboratory experiments involves estimating the unique contribution of plants to outcomes over and above the contributions of other workplace factors. Even experiments in field settings with existing groups of employees (i.e., quasi-experiments) should consider the effects of plants in relation to other workplace factors. However, this is a complicated task because any normal physical aspect of the workplace is of “marginal utility” in enhancing worker perceptions of their job situation (Brill et al., 1984). That is, the effects of plants may be very small against a background of numerous other workplace factors known to be potent.
The outcomes that have been of interest in research on plants in the work environment can be studied against the background of two general sets of workplace factors, physical and psychosocial. For decades, psychologists have realized that physical workplace factors have an important influence on employee satisfaction and productivity (Gifford, 2002). Particular levels and characteristics of sound, lighting, temperature, and air quality can contribute to negative appraisals of demands from the environment and in turn stress (Sundstrom, 1986). In support of this notion, numerous empirical studies have found associations between factors in the physical work environment and outcomes such as task performance, health, and stress (Gifford, 2002; McCoy, 2002; Sundstrom, 1986).
However, according to Bechtel (1997), cultural values and management styles are highly intertwined with the physical form of the work environment and cannot be seen as separate. It is therefore also necessary to investigate psychosocial workplace factors. The most commonly cited approach in research on psychosocial workplace factors is the job strain model (Karasek, 1979; Karasek and Theorell, 1990). This model, commonly called the demand–control model, attributes outcomes such as stress, health, and productivity to the interaction between job demands and the worker's control over the execution of tasks and other aspects of work. A large number of studies have found that the model predicts diverse health outcomes (e.g., Karasek et al., 1981; Schnall et al., 1994; Theorell et al., 1998). A more recent version of the model includes support from coworkers, which generally improves explanation of health outcomes (Karasek and Theorell, 1990; Kristensen, 1996).
Much of the literature on indoor plants treats their benefits as outcomes of psychological restoration. Restoration processes involve the renewal of psychological and physiological resources that normally become depleted in meeting ordinary demands (Hartig, 2004). The two restoration processes commonly cited in the literature on indoor plants concern recovery from an inability to concentrate characteristic of attentional fatigue (Kaplan, 1995) and recovery from the elevated physiological arousal and negative emotions characteristic of acute stress (Ulrich et al., 1991). In these processes, indoor plants are seen as features of the indoor environment that attract attention without effort and evoke positive emotions that can respectively promote renewal of the capacity to concentrate and interrupt the stress process. Note that attentional fatigue may contribute to stress; the person cannot concentrate well enough to meet demands, which the person then experiences as excessive and more stressful (Kaplan, 1995). It follows that directed attention restoration might play a role in reducing stress.
The stress process is a general one in that it mediates between an aggregate of demands from diverse workplace factors, on the one hand, and diverse immediate and longer-term outcomes on the other hand. Two of the outcomes selected for study here, sick leave and productivity, can plausibly be attributed, at least in part, to chronic stress resulting from workplace demands. Another outcome studied here, perceived stress, is thus generally seen as a mediator between environmental characteristics and health outcomes, but it is also an outcome variable that is important in its own right, reflecting as it does the worker's experience of demands.
Different research approaches will provide different kinds of information on the associations between indoor plants and important workplace outcomes (see Pearson-Mims and Lohr, 2000). To supplement the experimental studies performed to date, we present a cross-sectional survey conducted in workplaces. In this survey, the associations between indoor plants and perceived stress, sick leave, and productivity were investigated while statistically controlling for three sets of variables: physical aspects of the indoor work environment (e.g., noise, temperature, lighting, air quality); psychosocial factors (job demands, control at work, and social support from coworkers); and basic personal characteristics (age and gender) that plausibly influence levels of the workplace factors under study as well as the outcomes of interest (e.g., Karasek and Theorell, 1990). More specifically, the following question was addressed: Do indoor plants make a unique contribution to the explanation of perceived stress, sick leave, and productivity after controlling for other physical and psychosocial workplace factors that presumably feed into the same general mediating process that generates those outcomes? If our correlational evidence on this point agrees with the evidence from laboratory and field experiments, then it will strengthen the validity of claims about benefits of indoor plants (see Steptoe, 1997).
Brill, M., Margulis, S. & Konar, E. 1984 Using office design to increase productivity (Vols. 1–2) Workplace Design and Productivity Buffalo, N.Y
Bringslimark, T., Hartig, T. & Patil, G.G. 2007 The psychological benefits of indoor plants: A critical review of the experimental literature Manuscript (under review)
Clements-Croome, D. & Kaluarachchi, Y. 2000 Assessment and measurement of productivity Clements-Croome D. Creating the productive workplace E & FN Spon London
Cohen, J., Cohen, P., West, S.G. & Aiken, L.S. 2003 Applied multiple regression/correlation analysis for the behavioral sciences 3rd ed Erlbaum Mahwah, N.J
Cohen, S. & Williamson, G. 1988 Perceived stress in a probability sample of the United States 31 67 Spacapan S. & Oskamp S. The social psychology of health: Claremont Symposium on applied social psychology Sage Publ Newbury Park, Calif
Coleman, C.K. & Mattson, R.H. 1995 Influence of foliage plants on human stress during thermal biofeedback training HortTechnology 5 137 140
Dallner, M., Elo, A.L., Gamberale, F., Hottinen, V., Knardahl, S., Lindström, K., Skogstad, A. & Örhede, E. 2000 Validation of the general Nordic questionnaire (QPSNordic) for psychological and social factors at work Nordic Council of Ministers Copenhagen, Denmark
Eskin, M. & Parr, D. 1996 Introducing a Swedish version of an instrument measuring mental stress. Reports from the Department of Psychology No. 813 Stockholm University Stockholm
Ferrie, J.E., Kivimäki, M., Head, J., Shipley, M.J., Vahtera, J. & Marmot, M.G. 2005 A comparison of self-reported sickness absence with absences recorded in employers’ registers: Evidence from the Whitehall II study Occup. Environ. Med. 62 74 79
Fjeld, T., Levy, F., Bonnevie, C., Sandvik, L., Veiersted, B. & Riise, G. 1999 Foliage plants both with or without additional full-spectrum fluorescent light, may reduce indoor health and discomfort complaints Proc. Indoor Air 2 616 621
Fjeld, T., Veiersted, B., Sandvik, L., Riise, G. & Levy, F. 1998 The effect of indoor foliage plants on health and discomfort symptoms among office workers Indoor Built Environ. 7 204 209
Heerwagen, J., Heubach, J.G., Montgomery, J. & Weimer, W.C. 1995 Managing occupational stress through changes in the workplace environment AAOHN J. 43 458 468
Karasek, R.A., Baker, D., Marxer, F., Ahlbom, A. & Theorell, T. 1981 Job decision latitude, job demands, and cardiovascular disease Am. J. Public Health 71 694 705
Larsen, L., Adams, J., Deal, B., Kweon, B.S. & Tyler, E. 1998 Plants in the workplace: The effects of plant density on productivity, attitudes, and perceptions Environ. Behav. 30 261 281
Liu, M., Kim, E. & Mattson, R.H. 2003 Physiological and emotional influences of cut flowers arrangement and lavender fragrance on university students J. Ther. Hort. 14 18 27
Lohr, V.I., Pearson-Mims, C.H. & Goodwin, G.K. 1996 Interior plants may improve worker productivity and reduce stress in a windowless environment J. Environ. Hort. 14 97 100
Pearson-Mims, C.H. & Lohr, V.I. 2000 Reported impacts of interior plantscaping in office environments in the United States HortTechnology 10 82 86
Shoemaker, C.A., Randall, K., Relf, P.D. & Geller, E.S. 1992 Relationships between plants, behavior, and attitudes in an office environment HortTechnology 2 205 206
SPSS. 14.0 [Computer software] 2006 SPSS Inc Chicago
Steptoe, A. 1997 Stress and disease 174 177 Baum A., Newman S., Weinman J., West R. & McManus C. Cambridge handbook of psychology, health, and medicine Cambridge Univ. Press Cambridge
Sundstrom, E. 1986 Work places: The psychology of the physical environment in offices and factories Cambridge Univ. Press Cambridge
Theorell, T., Tsutsumi, A., Hallquist, J., Reuterwall, C., Hogstedt, C., Fredlund, P., Emlund, N. & Johnson, J.V.and the SHEEP study group 1998 Decision latitude, job strain, and myocardial infarction: A study of working men in Stockholm Amer. J. Public Health 88 382 388
Ulrich, R.S. & Parsons, R. 1992 Influences of passive experiences with plants on individual well-being and health 93 105 Relf D. The role of horticulture in human well-being and social development Timber Press Portland, Ore
Ulrich, R.S., Simons, R.F., Losito, B.D., Fiorito, E., Miles, M.A. & Zelson, M. 1991 Stress recovery during exposure to natural and urban environments J. Environ. Psychol. 11 201 230
Wolverton, B.C., Johnson, A. & Bounds, K. 1989 Interior landscape plants for indoor air pollution abatement: Final Rpt Plant for Clean Air, NASA, Stennis Space Ctr., Miss
Wood, R.A., Orwell, R.L., Tarran, J., Torpy, F. & Burchett, M. 2002 Potted-plant/growth media interactions and capacities for removal of volatiles from indoor air J. Hort. Sci. Biotechnol. 77 120 129