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HORTSCIENCE 44(2):384–391. 2009.
The Impact of Interior Plants in
University Classrooms on Student
Course Performance and on
Student Perceptions of the Course
and Instructor
Jennifer S. Doxey
1
and Tina Marie Waliczek
2,4
Department of Agriculture, Texas State University, 601 University Drive,
San Marcos, TX 78666
Jayne M. Zajicek
3
Department of Horticultural Sciences, Texas A&M University, College
Station, TX 77843-2133
Additional index words. interiorscape, human issues in horticulture, course evaluation,
instructor evaluation, academic responses, instructional ratings, houseplant
Abstract. The main objective of this research was to investigate the impact of plants
within a university classroom setting on course performance and on student perceptions
of the course and instructor. The study was designed to include a minimum of two classes
of the same coursework taught by the same professor in the same room during one
semester. Three sets of two classes each and 385 students were included within the study.
Throughout the semester, the experimental class of students was treated by including an
assortment of tropical plants within the classroom. Plants were not present in the control
classroom of the study. The official university course and instructor evaluation survey
was administered at the end of the semester. Additionally, each student provided
demographic data, including class rank, gender, and ethnicity. To measure course
performance, the professor for each course reported each student’s grade for the course.
No statistically significant differences were found in comparisons of grades/student
course performance (P= 0.192). However, statistically significant differences were found
in comparisons of overall course and instructor evaluation scores of treatment and control
groups (P= 0.065). Statistically significant differences were found in comparisons of the
individual courses/classrooms between control and treatment groups on statements in
subsections of the course and instructor evaluation survey, including the areas of
‘‘learning,’’ ‘‘enthusiasm (of instructor),’’ and ‘‘organization (of instructor).’’ In these
comparisons of the treatment and control groups, the differences that were most
apparent were in students who had class in the classroom that was windowless and
stark. The plants appeared to have the greatest impact on students in the room that was
void of other natural elements.
In the 1700s, interior plants were consid-
ered to be capable of suffocating a person
while they slept. Still, people kept plants in
their homes despite the warnings (Gowan,
1987), demonstrating an inherent desire for
plants. Today, an urbanized lifestyle has led
to people spending 80% or more of their time
in indoor settings (Fjeld et al., 1998). Many
individuals and businesses continue to en-
hance their homes or offices with interior
plants (Dravigne et al., 2008). Research has
suggested that interior plants may offer some
psychological and restorative values such as
reduced tension (Ulrich et al., 1991), better
coping mechanisms (Lohr and Pearson-
Mims, 2000), and increased ability for con-
centration and attention (Taylor et al., 2001).
A recent study found that employees in
offices with plants rated their job satisfaction
more positively when compared with em-
ployees in offices with no plants present
(Dravigne et al., 2008). Research has found
that interior plants can reduce eye irritation
and stress, motivate employees, improve
concentration, and even reduce air impurities
(Vitiello, 2001). Plants appeared to have a
positive effect on headaches and fatigue and
hoarseness; even dry facial skin was reported
with less incidence when plants were intro-
duced to offices (Fjeld et al., 1998; Laviana
et al., 1983).
The benefits of interior plants have been
shown to positively impact stress and pro-
ductivity. Reaction time on the computer
improved by 12% and a lower systolic blood
pressure was measured when plants were
placed in a computer laboratory along with
people’s reports of experiencing greater atten-
tiveness (Lohr et al., 1996). On one survey of
office employees and facilities managers,
only 10% of respondents thought that their
offices could be improved with plants, yet
60% of office workers liked having plants
around their desk. This was interesting in that
it was a higher percentage than the 50% who
rated the necessity of good technology as a
priority (Vitiello, 2001).
Research has focused on the types of interior
environments that promote good teaching and
learning (Think, 2003) and found that atten-
tion paid to the factors of ‘‘light, acoustics,
ventilation and ergonomics all contribute to a
positive experience for faculty and students’’
(p. 2). Windows that provided natural lighting
were important (Think, 2003), and rooms
with access to only artificial light have been
associated with ‘‘building sickness’’ (Robert-
son et al., 1989), which can lead to work-
related headaches and lethargy. Although the
subject of student and instructor preference in
classroom attributes is limited, one study
found that professors and students rated pos-
itive physical characteristics in classrooms
similarly (Douglas and Gifford, 2001).
Results found that classrooms with seating
arranged to promote interaction among stu-
dents, views of outdoor areas, and comfort-
able seating were preferred by both students
and faculty (Douglas and Gifford, 2001).
Using a survey of students (Dinsmore,
2003), a middle school teacher studied the
perceived effects of plants, lighting, and
music on students’ behaviors while in the
classroom. When asked if these three varia-
bles affected their learning, 43% of students
responded positively to the presence of plants
saying it created a more comfortable atmo-
sphere (Dinsmore, 2003). These numbers sup-
ported the teacher’s personal observations.
Research in schools has found that plants
benefit the classroom aesthetically and pro-
vide oxygen while absorbing toxins (Hart,
1999). In children with attention deficit dis-
order (ADD), more severe ADD symptoms
were seen in children when the interior
classroom environment was windowless and
void of natural elements (Taylor et al., 2001).
A study of university students found that
recovery from stress was shown to be greater
for those who had plants present during
testing (Russell and Uzzell, 1999).
This research supports that ‘‘A premium
should be placed on ensuring that all teaching
environments provide the best possible con-
ditions to stimulate learning. The teaching
environment affects how students rate their
course experience, and often affects the com-
fort level of not only the students, but also the
instructor within the classroom’’ (Think,
2003). Studies have shown that interior nat-
ural elements are important environmental
factors for universities that can cause stu-
dents to feel more comfortable, stimulating
social interaction and more time spent on
campus (Wiers-Jenssen et al., 2002).
The purpose of this study was to determine
if interior plants in university classrooms had
Received for publication 20 Oct. 2008. Accepted
for publication 18 Dec. 2008.
1
Graduate student.
2
Associate Professor.
3
Professor.
4
To whom reprint requests should be addressed;
e-mail tc10@txstate.edu.
384 HORTSCIENCE VOL. 44(2) APRIL 2009
an impact on student course performance and
on student perceptions of the course and the
instructor.
Materials and Methods
Study site. The study took place at a southern
university with an enrollment of 28,000
students at the time of the study. The main
campus has 225 buildings with some dating
back to the origin of the campus in 1903 and
some new buildings and classrooms that were
built in recent years to accommodate the
growing enrollment. The student enrollment is
diverse with a minority student population of
over 30%.
Instructors and courses. At the beginning
of the spring semester, instructors were se-
lected from the course catalog who met the
criteria of teaching the same course in the
same room with the same course material to
two or more separate groups of students.
These instructors were invited to participate
in the study. Instructors were offered free
weekly floral designs delivered to their office
throughout the semester as an incentive to
participate in the study. Three professors
agreed to participate. One taught two sections
of an introductory psychology course. Another
professor taught two sections of a sophomore-
level psychology course, and the third taught
two sections of an introductory sociology
course. All instructors held doctorates in the
fields in which they were teaching, and all
taught courses in the department for at least 3
years.
All six classes were offered during the
morning hours, and for uniformity within the
study, all control classes met first. However,
treatment and control classes for each in-
structor did not necessarily meet on the same
weekdays, although for each course, they all
met for the same amount of time (50 min or
1 h 15 min).
Enrollment in the treatment and control
classes for each course was not controlled
and varied somewhat between groups. The
introductory psychology course included 57
students in the treatment group and 37 students
in the control group, whereas the sophomore-
level psychology course included 45 students
in the treatment group and 44 students in the
control group. The introductory sociology
course included 97 students in the treatment
group and 104 students in the control group.
Therefore, because the classes and instructors
were not randomly chosen or assigned, results
of the study may not be generalized to the
overall population.
Plants. An assortment of plants was used
in each classroom with the logistics of the
room taken into consideration. Larger plants
used included Chrysalidocarpus lutescens
(Areca Palm), Ficus elastica (Rubber Tree),
and Dracaena marginata (Dragon Plant). For
hanging plants, Chlorophytum comosum
(Spider Plant), Hedera helix (English Ivy),
and Peperomia obtusifolia (Baby Rubber
Tree Peperomia) were used. An assortment
of foliage of various colors, sizes, and tex-
tures such as Spathiphyllum wallisii ‘Mauna
Loa’ (Peace Lily), small Kalanchoe bloss-
feldiana (Kalanchoe), and Epipremnum aur-
eum (Pothos) were used interchangeably.
Classrooms and plant placement. All
classes met within two buildings on campus.
In all classrooms, focus was given to the front
of the classroom for plant placement (Figs. 1
and 2), although an attempt was made to
place other plants in appropriate spots around
the classroom because visibility of the plants
could have been limited for some students
given their seating location. Student seating
was not assigned, and students had the option
in all classes of sitting in any available seat
throughout the semester. The introductory
psychology course met in a classroom on
the second floor of the Psychology Building
and seated 80 students. The room received
morning sunlight through a wall of windows
that faced south and had a view of large trees
that grew directly outside. Spacious areas
within the room allowed for ample opportunity
Fig. 1. Photographs of each of the treatment classrooms included in the study of the impact of interior plants in university classrooms on student course
performance and on perceptions of the course and instructor. The room in Aseated 80 students, whereas the room in Bseated 60 students. The auditorium in C
seated 121 students.
HORTSCIENCE VOL. 44(2) APRIL 2009 385
to place a variety of greenery throughout the
classroom (Fig. 1A).
The sophomore-level psychology course
classroom was a third floor classroom in the
Psychology Building (Fig. 1B). The room had
windows facing north that viewed the tops of
trees. The classroom was cramped with fur-
niture and media equipment crowded aisles.
A drape dangled from a window during a
portion of the semester and often the drapes
hid much of the window view of the trees
outside. One to three plants were hung in the
front or on the side of the room from the
ceiling tiles. Larger plants were also placed on
the floor and table surfaces in the front of the
classroom. The main entranceway into the
classroom was at the back of the classroom, so
a floor plant was often strategically placed to
be seen as students entered the room (Fig.
1B). The room held seating for 60 students.
The introductory sociology course class-
room was a modern but stark, windowless
auditorium with limited floor space. The
room seated over 100 students. Three to four
larger-sized plants were placed on the floor in
the front of the classroom on the right and on
the left side of the room where they would not
interfere with instruction but could be viewed
by students (Fig. 1C).
Plants were placed and removed quickly
and anonymously between classes. Students
in the treatment and control groups were not
informed of the study and its objectives.
When plants showed stress, they were re-
placed with healthier specimens.
Course and instructor evaluation instru-
mentation. A consent form was distributed
and collected that allowed for students to
volunteer anonymous information for the
research, and the research was approved by
the university Internal Review Board. Stu-
dents were offered a packet of seeds or a
candy bar as an incentive to participate in the
study. Professors provided all students with a
code number to use when responding instead
of their name so that all information provided
remained anonymous.
Surveys were distributed in each treat-
ment and control classroom during the last
2 weeks of the semester by the researchers.
Demographic data, including class rank
(freshman, sophomore, junior, senior), gen-
der, and ethnicity, were gathered. Questions
from the official university course evaluation
survey were used to collect information on
student perceptions of the course and the
instructor. Twenty-two questions covered the
categories of ‘‘learning,’’ ‘‘enthusiasm,’’ ‘‘orga-
nization,’’ ‘‘individual rapport,’’‘‘examinations,’’
‘‘assignments,’’ and ‘‘student and course charac-
teristics.’’ Students were instructed to rate each of
the 22 statements by choosing responses rated on
a Likert-type scale (Likert, 1967). The five re-
sponses were 5 = ‘‘strongly agree,’’ 4 = ‘‘agree,’’
3 = ‘‘neutral,’’ 2 = ‘‘disagree,’’ and 1 = ‘‘strongly
disagree.’’ The reliability of the overall instru-
ment used for this study was determined using the
Cronbach’s alpha reliability test and was found to
be 0.84 for this study indicating suitable reliability
(Gall et al., 2006).
Course performance data. Course grade
was determined by the instructors of each
course and was reported to researchers by each
instructor. Course grade measured course
achievement on the traditional 4-point scale
(A=4.0,B=3.0,C=2.0,D=1.0,andF=0.0).
The university involved in the study does not
use the plus and minus system of grading.
Scoring and data analysis. The section of
the instrument that measured student percep-
tions of the course and instructor were scored
by allocating 5 points for the most positive
answers and 1 point for most negative
answers given by each student on the Likert
scale (Likert, 1967). Responses were reverse-
coded when the most positive answer was
initially allocated the least amount of points.
Fig. 2. Photographs of each of the control classrooms included in the study of the impact of interior plants in university classrooms on student course performance
and on perceptions of the course and instructor. The room in Aseated 80 students, whereas the room in Bseated 60 students. The auditorium in Cseated 121
students.
386 HORTSCIENCE VOL. 44(2) APRIL 2009
Therefore, with 22 questions in total, each
student earned a score that ranged from 22 to
110. Individual scores were tabulated by the
primary researcher for the study and entered
into a Microsoft Exceläspreadsheet (Seattle,
WA).
The data collected were analyzed using
the Statistical Package for the Social Scien-
ces (SPSS) for Windows Release 11.5ä
(Chicago, IL). Statistical procedures included
descriptive statistics, frequencies, and analy-
sis of variance tests to determine differences
between overall grades and scores, categories
of responses, individual statements, and indi-
vidual course comparisons. The a priori alpha
level was set at 0.10, which is considered
suitable for research in the social and behav-
ioral sciences (Bennett, 1995; Borg and Gall,
1989; Kaplan, 1987).
Results and Discussion
The control group included 48.1% (185)
of respondents, whereas the treatment group
included 51.9% (200) of the sample. Demo-
graphic background of the control and treat-
ment groups was compared and found to be
statistically similar for gender (P= 0.373),
ethnicity (P= 0.606), and overall university
grade point average (GPA; P= 0.730).
Statistically significant differences were
found in the area of class rank (freshman,
sophomore, junior, senior) (P= 0.097) with
the treatment group having more freshman
when compared with the control group
(34.5% versus 28.6%) and the control group
having more seniors when compared with the
treatment group (14.1% versus 8%). Num-
bers of sophomores were similar for the
treatment and control groups (36% versus
36.2%) as were percent juniors included in
each group (20% versus 19.5%). Past re-
search has found that seniors tend to rate
courses more positively when compared with
other class ranks (Frey et al., 1975); there-
fore, researchers were not concerned with the
control group having more seniors and fewer
freshman because it would not benefit the
treatment group in terms of biasing the
variables of interest.
The overall sample included 137 males
and 246 females (and two respondents who
did not report gender). Most students were
undergraduate freshmen or sophomores (67.8%)
and white (69.1%). Although this sample was
similar to the overall population of students at
the university, the sample was self-selected
by the volunteering instructors of the courses
and the students who agreed to participate in
the study and therefore may differ from the
overall target comparison population
(Frankel, 1983).
Course performance. The first objective
of the study was to compare final course
grades of students in classrooms that had
plant material present during instruction with
final course grades of students in classrooms
with no plant material present. Course per-
formance was analyzed by comparing grades
issued by the course instructors on a 4-point
scale. An analysis of variance compared the
treatment and control groups’ grades and no
statistically significant differences were
found (P= 0.192; Table 1). Therefore, when
looking at the overall sample of students,
plants did not appear to distract students nor
benefit them during instruction. Research has
found that plants may help to improve con-
centration (Taylor et al., 2001; Vitiello, 2001)
and task performance (Shibata and Suzuki,
2004), which would, in turn, improve grades.
However, these overall findings did not
appear to support these studies in compar-
isons of the overall sample.
Course and instructor evaluation scores.
An analysis of variance compared the treat-
ment and the control groups’ overall scores
concerning perceptions of the course and the
instructor and found statistically significant
differences (P= 0.065; Table 1). The treat-
ment group scores were 1.52 points higher
than the control group scores (82.13 versus
80.61). The range of scores was much nar-
rower for the treatment group with the min-
imum and maximum scores being 59 and 100
compared with the control group’s minimum
and maximum scores of 29 and 100. Research
findings in areas of office work have shown
that plants can improve perceptions of the
work environment (Dravigne et al., 2008;
Fjeld et al., 1998; Lohr et al., 1996). This
research supports other studies with under-
graduate students that found that mood was
improved in rooms that contained a plant
(Shibata and Suzuki, 2004).
Statements on the course and instructor
evaluation inventory were analyzed individ-
ually to see where differences were occurring
in how respondents answered. Of the 22
statements, 10 individual statements were
found to be statistically significantly different
between treatment and control groups (Table
2). All of the statistically significant state-
ments were rated more positively by students
in the treatment group. It was interesting to
note that all of the categories that related
directly to in-class learning had some, and
sometimes all of the statements showing sta-
tistically significantly differences, including
the categories of ‘‘learning,’’ ‘‘enthusiasm,’’
‘‘organization,’’ and ‘‘student and course char-
acteristics.’’ Categories that had statements
that were less connected with daily in-class
situations, including ‘‘individual rapport,’’
‘‘examinations,’’ and ‘‘assignments,’’ had no
statements that were statistically significantly
different in comparisons between the control
and treatment groups (Table 2).
All four statements in the category of
‘‘learning’’ showed statistically significant
differences (Table 2). Statistical significance
was found in mean score comparisons of the
treatment and control group responses to the
statement, ‘‘I found the course challenging
and stimulating’’ (P= 0.096; Table 2). Mean
scores for the treatment group were higher
than those for the control group (4.04 versus
3.93). Mean scores were also statistically
significantly higher for the treatment group
on the statement, ‘‘I have learned something I
consider valuable’’ (P= 0.094; 4.29 versus
4.18; Table 2). There were differences in
treatment group versus control group
responses to the statement, ‘‘My interest in
the subject has increased as a consequence of
this course’’ (P= 0.014; Table 2). More
students in the treatment group (8.5%)
responded as agreeing or strongly agreeing
to the statement when compared with the
respondents in the control group. Nearly 11%
(10.8%) of the control group disagreed or
strongly disagreed with the statement com-
pared with 2.5% negative responses from the
treatment group. Additionally, statistically
significant differences were found concern-
ing the ‘‘learning’’ statement, ‘‘I have learned
and understood the subject materials in this
course’’ (P= 0.038). The treatment group
more often agreed or strongly agreed (6.5%)
when compared with control group responses
(Table 2). In the control group, 3.9% of
students indicated ‘‘disagree’’ or ‘‘strongly
disagree’’ compared with 2.0% in the treat-
ment group who indicated only ‘‘disagree.’’
Both statements in the ‘‘enthusiasm’’
category were found to be statistically sig-
nificantly different in comparisons between
treatment and control group responses. Treat-
ment group mean scores showed more
positive responses on the statement, ‘‘Instruc-
tor’s style of presentations held my interest
during most of the class time’’ when com-
pared with control group mean scores (P=
0.059; 4.13 versus 3.96; Table 2). On the
‘‘enthusiasm’’ statement, ‘‘Instructor seemed
interested in teaching the course,’’ the treat-
ment group had 4% more responses as
‘‘agree’’ or ‘‘strongly agree’’ in comparison
with the control group’s responses on the same
Table 1. Analysis of variance comparisons of overall treatment and control groups’ instructor-issued end-
of-semester grade
z
and overall course and instructor evaluation scores
y
in the study of the impact of
interior plants in university classrooms on student course performance and on perceptions of the course
and instructor.
Participant group Sample size (no.) Mean
z
SD df F P
Course grade
z
Treatment 190 2.65 1.017 1 1.706 0.192
Control 176 2.51 0.985
Overall course and instructor evaluation scores
y
Treatment 200 82.13 8.063 1 3.428 0.065*
Control 185 80.61 10.120
z
Grades were issued on a traditional 4-point scale by instructor with A = 4.0, B = 3.0, C = 2.0, D = 1.0, and
F = 1.0.
y
Scores ranged from 22 to 110. Twenty-two statements were rated on a 1 to 5 scale with 5 being the most
positive response and 1 being the most negative response.
*
Statistically significant at the 0.10 level.
HORTSCIENCE VOL. 44(2) APRIL 2009 387
Table 2. Analysis of variance comparing treatment and control groups’ individual statement response means
z
on the course and instructor evaluation instrument in
the study of the impact of interior plants in university classrooms on student course performance and on perceptions of the course and instructor.
Participant group Sample size (no.) Mean
z
SD df F P
Learning
I found the course challenging and stimulating.
Treatment 200 4.04 0.562 1 2.778 0.096*
Control 185 3.93 0.676
I have learned something I consider valuable.
Treatment 200 4.29 0.554 1 1.197 0.094*
Control 185 4.18 0.741
My interest in the subject has increased as a consequence of this course.
Treatment 200 4.10 0.780 1 6.154 0.014**
Control 185 3.87 0.992
I have learned and understood the subject materials in this course.
Treatment 200 4.18 0.610 1 4.318 0.038**
Control 184 4.04 0.723
Enthusiasm
Instructor’s style of presentations held my interest during most of the class time.
Treatment 200 4.13 0.858 1 3.583 0.059*
Control 185 3.96 0.881
Instructor seemed interested in teaching the course.
Treatment 200 4.64 0.531 1 5.929 0.015**
Control 185 4.49 0.700
Organization
Instructor’s explanations were clear.
Treatment 200 4.35 0.640 1 6.647 0.010**
Control 185 4.15 0.900
The assignments were carefully explained.
Treatment 199 4.29 0.684 1 2.556 0.111
Control 185 4.17 0.773
Instructor spoke clearly.
Treatment 200 4.51 0.558 1 7.024 0.008**
Control 185 4.34 0.728
Instructor spoke at a comfortable speed.
Treatment 200 4.39 0.685 1 1.027 0.312
Control 185 4.31 0.699
Individual rapport
Instructor made me feel welcome in seeking help/advice in or outside of class.
Treatment 200 4.21 0.810 1 0.430 0.512
Control 185 4.15 0.793
Instructor was adequately accessible to me during office hours or after class.
Treatment 200 3.94 0.818 1 0.899 0.344
Control 185 3.86 0.848
Instructor was helpful when I contacted her outside of class.
Treatment 192 3.76 0.855 1 0.393 0.531
Control 185 3.81 0.867
Examinations
Feedback on examinations was useful to me.
Treatment 197 3.78 0.838 1 0.000 0.992
Control 184 3.78 0.866
Feedback on graded materials was useful to me.
Treatment 198 3.74 0.806 1 0.343 0.558
Control 183 3.79 0.858
Methods on evaluating student work were fair.
Treatment 198 4.21 0.639 1 0.058 0.809
Control 184 4.19 0.726
Examinations tested course content as emphasized by the instructor.
Treatment 198 4.30 0.681 1 0.797 0.373
Control 185 4.23 0.755
Examinations reflected course content covered.
Treatment 199 4.29 0.707 1 0.004 0.947
Control 185 4.29 0.765
Assignments
Required readings were useful to me.
Treatment 200 3.69 0.882 1 1.030 0.311
Control 185 3.59 0.963
Required texts were useful to me.
Treatment 200 3.68 0.950 1 0.743 0.389
Control 184 3.59 1.041
Student and course characteristics
Level of interest in the subject before this course.
Treatment 200 2.98 0.961 1 2.834 0.093*
Control 184 2.81 1.020
Level of interest at this time.
Treatment 200 3.68 0.890 1 5.483 0.020**
Control 185 3.45 1.047
z
Statements were rated on a 1 to 5 scale with 5 being the most positive response and 1 being the most negative response.
*
Statistically significant at the 0.10 level.
**
Statistically significant at the 0.05 level.
388 HORTSCIENCE VOL. 44(2) APRIL 2009
statement (P= 0.015; Table 2). Only one
person (0.5%) of the 200 responses indicated a
negative ‘‘disagree’’ in the treatment group,
whereas three persons (1.6%) of the 185
control group responses indicated they dis-
agreed, two of those being ‘‘strongly dis-
agree’’ (P= 0.015; Table 2).
Two of four statements in the ‘‘organiza-
tion’’ category were found to be statistically
significant in comparisons of the treatment
and control group responses. The statement,
‘‘Instructor’s explanations were clear’’ had
statistically significant differences in com-
parisons of the treatment to the control group
responses (P= 0.010; Table 2). Over 5%
more of the treatment group responded pos-
itively to the statement, ‘‘The assignments
were carefully explained’’ when compared
with control group responses. Quantitative
response to ‘‘Instructor spoke clearly’’ was
4% more positive (P= 0.008) within the
treatment group (Table 2).
When rating statements concerning levels
of interest at the start of the course versus the
levels at the end of the course, statistically
significant differences were found in the
levels of interest students perceived they
had in the subject before the course began
(P= 0.093; Table 2) and at the time of the
course and instructor evaluation (P= 0.020;
Table 2). On both statements, the treatment
group rated the statements more positively
when compared with the control group.
However, the differences between groups
were much more evident on how students
rated their interest levels at the end of the
course with almost 9% more students in the
treatment group rating their interest levels as
‘‘high’’ or ‘‘very high’’ when compared with
the control group (58.5% in the treatment
group versus 50.3% in the control group).
These overall findings in comparisons of
individual statements are compatible with
research that found plants improve the class-
room aesthetically (Hart, 1999) and that 43%
of young students felt the presence of plants
creates a more comfortable learning environ-
ment (Dinsmore, 2003).
Individual classroom/course comparisons.
Researchers were interested in comparing
individual classrooms/courses. Demographic
comparisons were made before comparisons
and no differences were found in comparisons
of ethnicity (P= 0.338), class rank (P=
0.135), or GPA (P= 0.242). Statistically
significant differences were found in compar-
isons of gender with the sophomore-level
psychology course having more females
(76.1%) in comparison with the introductory
psychology course (61.7% female) or the
introductory sociology course (60.2% female)
(P= 0.028). The limitations these differences
presented in the data set were considered
during interpretation of the analysis.
When comparisons were made between
classrooms/courses of students, no differen-
ces were found in comparisons of treatment
and control groups of students in the intro-
ductory psychology course in the well-main-
tained second floor classroom in comparisons
of student course grades (P= 0.480) or in
comparisons of course and instructor evalu-
ation scores (P= 0.964). The introductory
psychology course met in a sunny classroom
with ample room for interior plants, win-
dows, and a view of trees. Window views of
green leaves on trees outside this classroom
may have influenced students and made the
influence of the plants in the classroom less
pronounced. This would support other re-
search stating that students preferred class-
rooms with views of the outdoors (Douglas
and Gifford, 2001).
Analysis of the treatment and control
group of students in the sophomore-level
psychology course in the third floor cramped
classroom revealed differences in distribu-
tion of course grades (P= 0.005; Table 3)
with treatment group grades averaging higher
when compared with the control group.
Grade distribution for the course revealed
21.9% more grades of ‘‘A’’ in the treatment
group when compared with the control group,
8.3% more grades of ‘‘B’’ in the treatment
group than in the control group, and 16.5%
more responses of ‘‘C’’ in the control group
when compared with the treatment group.
No statistically significant differences (P=
0.705) were found in the overall course and
instructor evaluation scores between the treat-
ment and control groups in the third floor
cramped classroom with windows. However,
in interviews with the professor of the soph-
omore-level psychology classes, she stated
that she felt attendance was better, class
participation was better, and class average
on most tests was higher in the class with
plants.
Window views in the sophomore-level
psychology classroom were often blocked
by dark drapes. The green view of the tops
of trees was not as lush and bright from the
third floor as were the views from the second
floor on the other side of the building in the
introductory psychology classroom. There-
fore, it is possible indoor plants may have had
a slightly greater effect on course grades in
the third floor classroom when compared
with the second floor classroom. Addition-
ally, although research indicates that gender
and grades are not necessarily correlated
(MeCornack and McLeod, 2005), it may be
important to note that this course and class-
room had a statistically significantly greater
number of females in comparison with the
other courses and classrooms that could have
impacted results.
There were no statistically significant
differences found in overall course grades
in comparisons of the treatment and control
groups of students enrolled in the introduc-
tory sociology class held in the large audito-
rium (P= 0.750). However, there were
differences in the overall course and instruc-
tor evaluation scores (P= 0.049; Table 3) and
several statistically significant differences in
comparisons of students’ responses to indi-
vidual statements on the course and instructor
evaluation instrument (Table 4). Statistically
significant differences were found on 12 of
the 22 survey questions, including all ques-
tions in the categories of ‘‘learning,’’ ‘‘enthu-
siasm,’’ and ‘‘organization’’ (Table 4). As
shown in previous comparisons of the overall
sample, those categories that were less influ-
enced by in-class interactions (‘‘individual
rapport,’’ ‘‘examinations,’’ and ‘‘assign-
ments’’) had nearly all statements lacking
statistically significant differences in com-
parisons of the treatment and control groups
(Table 4). Students in the treatment group did
rate the statement, ‘‘Required readings were
useful to me’’ more positively when com-
pared with the control group (P= 0.093;
Table 4) as well as their level of interest in the
course at the time of the evaluation as being
higher (P= 0.025; Table 4).
The introductory sociology class had no
windows, was modern and in good repair,
but stark. It seated 121 people in an audito-
rium-style room that was painted white.
Plants appeared to have contributed to the
comfort, attention, and concentration of stu-
dents in the stark, windowless auditorium
more than in the psychology classes, which
had windows and a view of trees with
green leaves. These results supported re-
search on worker productivity that found
that, in offices with plants, productivity and
attentiveness increased, whereas blood pres-
sure and mental fatigue decreased (Lohr
et al., 1996).
Instructor interviews. A brief interview
was conducted with each participating pro-
fessor to assess if plant material affected the
Table 3. Statistically significant analysis of variance comparisons of course grades
z
and overall course and
instructor evaluation scores
y
of treatment and control groups for the sophomore-level psychology class
and introductory sociology class in the study of the impact of interior plants in university classrooms on
student course performance and on perceptions of the course and instructor.
Participant group
Sample size
(no.) Mean
z,y
SD df F P
Sophomore-level psychology
Course grades
z
Treatment 44 3.14 0.795 1 8.353 0.005**
Control 39 2.62 0.847
Introductory sociology
Overall course and instructor evaluation scores
y
Treatment 97 80.78 8.502 1 3.914 0.049**
Control 104 78.25 9.574
z
Grades were issued on a traditional 4-point scale by instructor with A = 4.0, B = 3.0 ,C = 2.0, D = 1.0, and F = 1.0.
y
Scores ranged from 22 to 110. Twenty-two statements were rated on a 1 to 5 scale with 5 being the most
positive response and 1 being the most negative response.
**
Statistically significant at the 0.05 level.
HORTSCIENCE VOL. 44(2) APRIL 2009 389
way they felt while conducting class as well
as their perception of the reaction and behav-
ior of the class toward the presence of plants.
A verbal interview was held with the pro-
fessor of introductory psychology. Written
interviews were received from the professors
of the sophomore-level psychology and intro-
ductory sociology classes.
The professor of the introductory psychol-
ogy course stated in an informal interview
that she very much enjoyed the presence of
plants in the classroom and felt the presence
of plants might, unconsciously, have an
effect on her presentation to the classroom.
This supports other research that indicated
that instructor mood could be improved by
the presence of plants (Shibata and Suzuki,
2004) or that instructors could perceive a
more comfortable learning environment
(Dinsmore, 2003) in the presence of plants.
Past research also indicates that plants can
help increase attentiveness or decrease men-
tal fatigue (Lohr et al., 1996).
Written interviews with the instructors of
the sophomore-level psychology course and
the introductory sociology course stated that
they did not notice plants during instruction,
although both instructors indicated they liked
plants. The introductory sociology professor
stated that class participation was higher in
the treatment classroom, but absences did not
seem to be affected. Other research states that
plants can trigger positive emotions (Isen,
1990), which may help to encourage discus-
sion in a classroom environment.
The sophomore-level psychology profes-
sor stated she felt attendance was better in the
class with plants, although she did not know
if it was the result of the plants or perhaps the
later time of day. The instructor also felt class
participation was better in the class with
plants, although she named a number of
variables unrelated to plants that might have
affected that participation. She noted that
class average on most tests was higher in
the class with plants, again adding that other
variables not related to plants could have
affected scores. However, if this observation
was true, it would support research findings
that plants can positively affect a person’s
emotional state (Ulrich, 1981), which bene-
fits cognitive functioning necessary for mem-
ory recall (Isen, 1990).
Conclusions
Results from the study found that interior
plants appeared to have the greatest impact
on students participating in the classroom
environment that had no other natural ele-
ments. Results also showed that interior
plants can be a suitable alternative in some
cases to architectural elements such as win-
dows. Research has found that passive en-
counters with nature can improve levels of
satisfaction with job and home life and can
affect mood and cognition (Kaplan and
Kaplan, 1989; Sheets and Manzer, 1991;
Shibata and Suzuki, 2004). This study supports
Table 4. Analysis of variance comparisons of treatment and control groups’ individual statement response means
z
from the course and instructor evaluation
instrument for students in the introductory sociology course in the study of the impact of interior plants in university classrooms on course performance and on
perceptions of the course and instructor.
Participant group Sample size (no.) Mean
z
SD df F P
Learning
I found the course challenging and stimulating.
Treatment 97 4.09 0.631 1 6.128 0.014**
Control 104 3.87 0.669
I have learned something I consider valuable.
Treatment 97 4.25 0.613 1 4.961 0.027**
Control 104 4.04 0.709
My interest in the subject has increased as a consequence of this course.
Treatment 97 4.07 0.820 1 5.759 0.017**
Control 104 3.75 1.059
I have learned and understood the subject materials in this course.
Treatment 97 4.18 0.595 1 4.075 0.045**
Control 103 3.98 0.754
Enthusiasm
Instructor style of presentations held my interest during most of the class time.
Treatment 97 4.07 0.927 1 4.486 0.035**
Control 104 3.80 0.907
Instructor seemed interested in teaching the course.
Treatment 97 4.62 0.567 1 8.778 0.003**
Control 104 4.35 0.721
Organization
Instructor’s explanations were clear.
Treatment 97 4.27 0.685 1 10.366 0.001**
Control 104 3.88 0.969
The assignments were carefully explained.
Treatment 96 4.22 0.714 1 6.272 0.013**
Control 104 3.96 0.736
Instructor spoke clearly.
Treatment 97 4.49 0.580 1 6.561 0.011**
Control 104 4.26 0.710
Instructor spoke at a comfortable speed.
Treatment 97 4.43 0.691 1 3.134 0.078*
Control 104 4.26 0.697
Assignments
Required readings were useful to me.
Treatment 97 3.56 0.924 1 2.853 0.093*
Control 104 3.33 0.999
Student and course characteristics
Level of interest in the subject at this time.
Treatment 97 3.52 0.937 1 5.103 0.025**
Control 104 3.19 1.080
z
Statements were rated on a 1 to 5 scale with 5 being the most positive response and 1 being the most negative response.
*
Statistically significant at the 0.10 level.
**
Statistically significant at the 0.05 level.
390 HORTSCIENCE VOL. 44(2) APRIL 2009
other research showing that plants have value
beyond aesthetics in interior environments
(Dravigne et al., 2008; Liu et al., 2003; Lohr
and Pearson-Mims, 2000; Lohr et al., 1996;
Taylor et al., 2001), including promoting
positive feelings in university students. More
research should be conducted on the influ-
ence of plants on classroom instructors
because, in interviews, one professor noted
that she may have been unconsciously
affected by the presence of the plants in the
room. Because this factor was not specifically
measured in this research, the impact of the
plants on instructors’ teaching may be a
confounding factor in this research.
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