INTERIOR PLANTS MAY IMPROVE WORKER PRODUCTIVITY AND REDUCE STRESS IN A WINDOWLESS ENVIRONMENT 1)

This study documents some of the benefits of adding plants to a windowless work place a college computer lab. Participants' blood pressure and emotions were monitored while completing a simple, timed computer task in the presence or absence of plants. When plants were added to this interior space, the participants were more productive (12% quicker reaction time on the computer task) and less stressed (systolic blood pressure readings lowered by one to four units). Immediately after completing the task, participants in the room with plants present reported feeling more attentive (an increase of 0.5 on a self-reported scale from one to five) than people in the room with no plants. Index words: blood pressure, foliage plants, house plants, human issues in horticulture.  This study provides further justification for the use of interior plants in a variety of indoor settings. Many people feel that adding plants to interior spaces improves worker productivity and satisfaction, yet there are few, if any, concrete studies examining these impacts. Studies showing an impact on blood pressure, for example, have used videotapes of plants in natural settings, not live containerized plants in interior settings. This study, using common interior plants in a computer lab, confirms that interior plants can contribute to reduced stress. This study also documents that worker productivity on tasks requiring concentration and quick reactions can improve when plants are added to a work space.  Interior plants are common in many homes, work places, and commercial settings. Interior-scaping is widespread in the hospitality industry, where its presence has been shown to boost occupancy rates and generate profit (3). Intuitively, people sense that contact with plants and nature is restorative and calming to the human spirit. This widespread belief is evidenced by the extensive landscaping in residential communities, the use of plants in theme parks and other segments of the tourist industry, the growth of urban and community gardening, and interior plantscaping of office and retail spaces (10, 13). In the 1960s, the Interior plants may improve worker productivity and reduce stress in a windowless environment – From ‘Plants-for-People’ 2 open-plan "office landscape" characterized by the abundant use of large potted plants to separate work spaces, was popular (14). Although the office environment has changed over time, interior plants continue to be used in work spaces. As jobs become more technologically complex, the frequency of stress-related disorders in work environments increases (12). The need for a thorough understanding of the relationship between plants and human well-being is increasingly important (10). Interaction with plants, both passive and active, can change human attitudes, behaviours, and physiological responses (10). The stress-reducing benefits of passively viewing plants in natural settings are well documented (5, 9, 15, 16); however, many workers labour in windowless office spaces with few opportunities to view nature. Research indicates that workers in such windowless environments have lower job satisfaction and rate the physical conditions of their work as less "pleasant and stimulating" than people in windowed settings (4). Plants are widely used to personalize and decorate offices, and they are important in improving satisfaction with indoor space (7, 13). Accounts of studies conducted in Germany in the 1960s assert that improved employee morale, decreased absenteeism, and increased worker efficiency result when plants are added to office spaces compared to traditional, unplanted offices (1, 2). In the 1980s, reviews of the merits of interior landscaping continued to suggest that plants boost employee productivity, even by as much as 10% to 15%, when incorporated in offices and other work areas (8, 11). These reports of increased worker productivity in interiorscaped offices and work areas have been common; yet, we have been unable to find any research studies to substantiate these claims. The goal of these experiments was to examine the impacts of interior plants in windowless working environment on human well-being and productivity. Responses of subjects in the presence and absence of plants were compared.  Experimental setting. Experiments were conducted in a Washington State University instructional computer laboratory with 27 computer workstations. The room was 13.5 m (44 ft) long, 7.3 m (24 ft) wide, and 2,6 m (8,5 ft) high. It had no windows and was illuminated with overhead fluorescent lights. The walls had no ornamentation and there was a white markerboard across the front of the room. Most of the interior of the room was off-white; the desk tops were burnt orange. The conditions in the room averaged 27C (80F), 38% relative humidity, and 420 lux (38 fc) at the work surface during both experimental treatments. Interior plants may improve worker productivity and reduce stress in a windowless environment – From ‘Plants-for-People’ 3 Subjects. A majority of the 96 participants were volunteers from an undergraduate agricultural economics class. They ranged from 18 to 46 years old, and 78% were less than 25 years old. Half of the subjects were male and half were female. Eighty-four percent of the subjects were university students; the remainder were university employees or members of surrounding communities. All of the subjects had used computers before, and most used computers at least once a month. Half of the subjects reported their keyboarding skills as average and 30% felt that they were faster than average. When asked if they liked plants, 81% said "yes" and the remainder had either no opinion or said "no". Sixty-six percent had plants at their homes or offices. Correlations between responses to the demographic survey and treatment assignment were examined. There were no significant correlations between any of the demographic variables and treatment, except for that of having plants at home or work. Approximately 75% of the subjects in the treatment without plants had plants in their homes or work areas, while only 58% of those assigned to the treatment with plants had plants at home or work. Statistics examining the treatment by demographic response for this variable and others that might have explained the results were also examined, and no significant or meaningful relationships were found. For example, people's levels of computer expertise did not influence how they responded to the treatments. These analyses confirmed that there were no meaningful differences between subjects in the treatment groups and that the demographic variables were not useful in interpreting the results. For this reason, only the results for all subjects within a treatment will be reported, and the statistics for responses will not be categorized based on demographic responses. A preliminary experiment, with slightly different procedures, formed the basis for this experimental design. The majority of the 160 subjects in the preliminary experiment were volunteers from an upper level psychology class at WSU, and their average age was 20. Productivity. A computer program to test productivity and induce stress was specifically designed for these experiments by the senior author and created by a computer specialist in Informa-tion Systems at Washington State University. Tests of reaction time are used to obtain an objective measure of mental processing (17). Our program randomly displayed one of three shapes of different sizes, in various locations, at random time intervals, on the computer screen. The variables that were incorporated into this program have been associated with differences in reaction times (17). Participants were asked to press a key that corresponded with the shape on the screen as quickly as possible after they recognized the shape; therefore, subjects had a choice of three responses. Measures of reaction time where respondents have more than one possible response are associated with complex mental functioning and are considered appropriate instruments to measure performance under stressed or fatigued conditions (17). Interior plants may improve worker productivity and reduce stress in a windowless environment – From ‘Plants-for-People’ 4 One hundred symbols were presented in the same randomized sequence to each subject, thus keeping the complexity of the task identical for all subjects. The time interval after pressing the correct key, which cleared the screen, until the next symbol appeared varied from zero to five seconds. For each symbol presented, the number of wrong keys pressed and the time delay before pressing the correct key (reaction time) were automatically recorded in a computer file. In the preliminary experiment, only 50 symbols were presented, and the time delay between symbols ranged from one to 15 seconds, making the task somewhat more boring than the task used in the final experiment. The computer program concept and content were reviewed by a psychologist who considered it an appropriate instrument to measure reaction time. The program was pretested on various computers to ensure accurate recording of readings. A group of computer users also pretested the program to determine ease of usage. Blood pressure readings recorded while using the program confirmed that the program was effective in inducing stress. Stress measures. Emotional states, blood pressure, and pulse were measured for participants during the experiment. The Zuckerman Inventory of Personal Reactions (ZIPER) was used to monitor emotional states (18). Respondents indicated, on a scale from one to five, the degree to which each statement, such as "I feel sad," described the way they felt at that moment. An Omron Model HEM-713C automatic oscillometric digital bloo