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Rodiek, S (2002). Influence of an
Outdoor Garden on Mood and Stress in
Older Persons. Journal of Therapeutic
Horticulture, Volume XIII, 13-21
Influence of an Outdoor Garden on Mood and Stress in Older Persons
Susan Rodiek
Despite recent interest in healing gardens and therapeutic landscapes at residential
care facilities, few empirical studies have measured health outcomes in elderly
populations. This study explored methods for assessing psychological and
physiological outcomes associated with natural environments. Seventeen residents
ranging from 71 to 98 years of age (mean 84.7) engaged in the same activities at an
outdoor horticultural garden or indoor classroom. Before and after the experience,
subjects were assessed for positive and negative mood, anxiety, and salivary cortisol.
No significant change was found in mood or anxiety level. Cortisol was significantly
lower in the garden environment compared with the indoor settings, indicating
greater reduction in stress level. This pilot study supports previous research finding
health-related outcomes associated with brief exposure to natural environments.
Introduction
Throughout the centuries nature has been considered to have healing potential. Plants, sunlight
and other nature elements have often been incorporated in healthcare settings as a therapeutic
adjunct and to improve the atmosphere for patients, staff and visitors (Lewis, 1996; Gerlach-
Spriggs, Kaufman & Warner, 1998; Cooper Marcus & Barnes, 1999). A growing body of
research is offering evidence that contact with natural environments may result in improved
health outcomes. Studies in general and healthcare populations have measured muscle tension,
blood pressure, heart rate and immune response, as well as emotional status, attentional capacity
and other indicators of psychological condition (Hartig, Mang & Evans, 1991; Ulrich et al.,
1991; Ulrich & Parsons 1992; Ulrich, 1999). However, few outcome-based studies have been
conducted with aging populations. Although landscape and horticulture professionals may
observe therapeutic outcomes in elderly subjects, unquantified reports may be difficult to
translate into justification for reimbursement policies. Controlled empirical studies with plants
and garden environments may help increase the credibility of horticulture-related treatments and
advance the understanding of specific outcomes in different populations.
Preference-Based Studies
The available preference-based research generally indicates that older adults highly value contact
with plants and natural environments. For example, Perkins (1998) found that elderly residents
of congregate facilities considered plants, especially flowers, to be extremely important, along
with sunlight, fresh air, and views of water, wildlife and other nature elements. Talbot and
Kaplan (1991) also found nature important to the elderly, especially flower gardens and outdoor
sitting areas, and that having nature nearby substantially contributed to residential satisfaction.
Lewis and Mattson (1988) found that the preferences of nursing home residents for horticultural
activities far exceeded their actual frequency of participation, suggesting that appropriate
opportunities might not have been available. A study by Stoneham and Jones (1997) found that
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many aspects of gardening were of interest to residents of sheltered housing, even though the
environment was not always conducive to the realization of these desires. In private urban
gardens located within the community, Dunnett and Qasim (2000) found that the time spent
gardening was greatest in respondents over 65 years, suggesting that interest in nature may
increase with aging.
Outcome-Based Studies
In spite of these indications of the value of nature and gardening to the elderly, studies measuring
health-related outcomes associated with plants and nature elements are scarce, although some
exist. A large study with low-income urban elderly found that trees, plants and green lawns were
correlated with stronger social integration of residents, which in turn is associated with positive
health benefits (Kweon, Sullivan & Wiley, 1998). Langer and Rodin (1976) found beneficial
effects in elderly nursing home residents who cared for a plant as part of a program to enhance
sense of control. Residents given more control showed greater alertness and participation in
activities, and were found to have improved health and mortality rates measured eighteen months
later (Rodin & Langer, 1977). Mooney and Nicell (1992) found dementia-related agitation was
less in facilities with purposively designed outdoor areas than in ordinary facilities, but other
differences between the facilities may have contributed to the differences. In studying a
horticultural therapy program, Mooney and Milstein (1994) found specific benefits to elderly
residents, but the effect of plants was not separated from the effects of therapy. Whall et al.
(1997) found less agitation and aggression in bathing dementia patients when they were shown
pictures of plants and animals, but the effects were not separated from food and other stimuli. A
study comparing an Eden Alternative facility with a conventional facility found no benefit from
the extensive use of plants and other elements that are part of the Eden philosophy. However,
facilities and residents differed in other ways, and the study was conducted during the first year
of Eden implementation, while a major transition in policies and procedures was underway
(Coleman et al., 2002). Although these and other studies clearly contribute to the state of
knowledge, the literature on this topic still lacks a sufficient number of controlled, outcome-
based studies which separate the effects of plants and nature elements from other therapeutic
benefit such as increased activity and social contact. Only by isolating plants and nature-related
elements can we establish that horticulture is having an effect, in addition to therapy.
The Present Study
This pilot study tested methods for comparing environmental effects by randomly assigning
subjects to the same activities in either a garden or non-garden setting. The garden setting was
lush and flowery, the indoor settings reasonably pleasant but lacking in nature elements. Before
and afterward, subjects were assessed for mood and stress indicators. It was hypothesized that
outdoor garden subjects would have more positive changes than indoor subjects, based on: 1)
the expressed preference of older adults for plants and nature elements, and 2) nature-related
health outcomes found in other populations. Because contact time was brief, it seemed likely
that any difference found between the two groups would be modest. However, even minor
differences could have important implications for the health benefits possible from long-term
contact with plants and garden environments.
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Method
Selection and Recruitment of Subjects
Subjects were recruited from a residential complex for aging, comprised of a single-story nursing
facility (private-pay) with adjacent low-rise senior apartments (HUD-financed). Facilities shared
staff and administration, and were located on the same campus in a mid-size town in the southern
United States. Resident participation was restricted to the apartment complex and the two most
independent nursing wings, as administrators considered residents of the two remaining nursing
wings too frail or cognitively impaired to participate. Recruits from the two facility types were
randomly assigned in representative proportion to the different experimental conditions.
Recruitment was voluntary, and was solicited by announcements at mealtime when most
residents were present. Forty-four percent of the recruits came from the nursing home, and fifty-
six percent from the apartments. The nursing director reviewed the list of recruits for cognitive
and physical eligibility, and none were excluded from participation.
Subject Profile
The seventeen subjects ranged from 71 to 98 years of age (mean 84.7). Apartment subjects
averaged 80.8 years, compared with 89.8 years for nursing home subjects. Average length of
residence at the facility was 5.1 years for apartment subjects, and 3.9 years for nursing home
subjects. All subjects spoke English as their first language, and were female (the only male
recruit withdrew on the morning of the experiment). Assistive devices were used by about one
third of the subjects, and were distributed fairly evenly to the different treatment conditions:
there were three canes, two walkers, and one wheelchair.
Study Design
This study measured four variables on the subjects immediately before and after a single session
in one of three different randomly assigned conditions. The variables measured were positive
and negative mood, anxiety, and salivary cortisol. The assigned conditions were three different
environments: two indoor treatments and one outdoor treatment. Aside from elements relating to
nature or the outdoors, other aspects of the treatment environments were designed to be as much
alike as possible. For example, subjects used the same type of chair and tablecloth in each
setting, and research assistants read from a prepared script, following the same schedule. To
reduce the effect of extraneous variables, external events (such as people walking by) were
reduced to a minimum, and all sessions were conducted simultaneously. To increase the
independence of their responses, subjects were instructed not to hold conversations or discuss
their responses during the session. Subjects were observed to follow these instructions, but non-
verbal interactions might have influenced responses. The outdoor group had six subjects, and the
two indoor groups had five and six subjects each.
Environmental Conditions
The outdoor environment consisted of an umbrella table set up near a tree at a university
horticultural garden. Two indoor treatment environments were used, chosen to be as much alike
as possible: a classroom located at the horticultural garden; and an activity room at the subjects’
residential facility. Allowing one group to stay at the facility was intended to control for the
“field trip” effect; this group also did a few minutes of mild exercise to compensate for the
physical activity of the travel component. Each environment was arranged for subjects to sit
3
comfortably around a table, with a research assistant and facility staff member nearby. Weather
was a major environmental variable, and had to be comfortable for older adults, but not
necessarily a “perfect” day. The experiment was conducted in early spring, with a light breeze
and the sky about 40% cloudy. The temperature indoors was about 73 degrees Fahrenheit, and
outdoors about 68 degrees (considered barely warm enough by staff), but was warmed by
occasional sunshine. Ambient light levels (measured at the center of each table) were in the
same range for both indoor settings, 61 and 90 foot-candles, which is typical for fairly bright
indoor rooms (one foot-candle equals one lumen per square foot, or about 10.8 lux). The light
outdoors was much brighter (890 foot-candles), even though measured on a partly cloudy day
under a ten-foot-wide dark green umbrella. Higher light levels are characteristic of outdoor
environments, and were anticipated as an important aspect in which the treatment environments
would differ.
Environmental Contrast
To emphasize the difference between the two types of environments, nature elements were added
to the garden setting, and removed from the indoor settings. For example, the outdoor setting was
located where vegetation screened the view of nearby buildings, and flowering plants such as
potted bougainvillea were added. At the indoor settings, plants and nature paintings were
systematically removed, and the windows covered with sheer white paper which allowed natural
light but no direct views to the outdoors. The purpose of increasing or reducing the nature
content of the environmental settings was to clearly distinguish between effects due to nature and
non-nature elements, and to maximize the contrast of what was expected to be a very subtle
effect, considering the brief exposure subjects would have during this experiment.
Measures
Study settings and instruments were designed to accommodate physical and sensory limitations
common in older adults. Treatment locations were examined for safety hazards, and the outdoor
environment was located where it would be protected from the wind. Research assistants were
trained to give verbal instructions slowly and clearly. Questionnaires were presented in large
type (Arial 14 point), and formatted for maximum legibility. The measures of psychological
well-being used in the experiment were: positive mood, negative mood, and anxiety. Salivary
cortisol was measured as a stress marker, and was included for three reasons: First, as a
biological measure, cortisol does not rely on the interpretation of test questions or subjective
perception of emotional state. Second, it should be unaffected by acquiescence or fear of
retribution, which are common on psychological tests with an institutionalized population.
Third, because cortisol is closely associated with physical health and well-being, any
environmental feature which affects cortisol might have important implications for the health of
older adults (see Vogt, 1992, pp. 214-218 for an overview).
Mood (affect). Positive and negative mood were assessed with a ten-item scale
(Philadelphia Geriatric Center Positive and Negative Affect Rating Scale, Lawton, Kleban,
Dean, Rajagopal, & Parmelee, 1992; see also Kane & Kane, 2000). This scale was designed
specifically for use with older adults, is brief enough to administer repeatedly, and measures
positive and negative domains independently. The negative constructs represented are
depression (sad, depressed), anxiety (worried), and hostility (irritated, annoyed). The positive
constructs are feeling interested, energetic, happy, warmhearted, and content. For this study,
4
questions were phrased as “How strongly do you feel this way right now?” Responses used a
five-point scale from Not at All to Very Strong, with possible scores ranging from five to
twenty-five on each domain.
Anxiety. Participants’ level of anxiety was assessed with a ten-item subscale of the
widely used Spielberger State-Trait Anxiety Inventory (STAI), considered appropriate for
repeated measurements (Spielberger et al., 1979; Spielberger, Gorsuch, Lushene, Vagg &
Jacobs, 1983). This measure was chosen because of the uncomplicated questions and lack of
somatic items. Ten items indicate the presence or absence of anxiety, such as “I feel calm” or “I
am tense.” Respondents were asked to “circle the answer which describes your feelings right
now,” from Not At All to Very Much, using a four-point scale with possible scores ranging from
ten to forty.
Cortisol. Participants’ level of cortisol was assessed from saliva, which provided a non-
invasive approach useful for repeated measurements. Salivary cortisol is considered a reliable
measure of serum cortisol, and the short time lag of 20-30 minutes between stimulus and salivary
cortisol response (Kirschbaum & Hellhammer, 1994; Reid, Intieri, Susman, & Beard, 1992) was
suitable for this study. As an adrenal hormone stimulated by the hypothalamic-pituitary-adrenal
axis during a difficult or hopeless situation, cortisol is commonly considered a biological
indicator of stress (Brannon & Feist, 1997; Vogt, 1992). Prolonged exposure to high cortisol
level has been associated with hypertension, osteoporosis, muscle atrophy, fatigue, lowered
immune function and coronary heart disease (Raff et al., 1999; Samuels, Furlan, Boyce, & Katz,
1997). High cortisol level is also frequently associated with depression. Cortisol-lowering
agents have been used successfully to treat depression, although the role of cortisol in depression
is not fully understood (Cowen, 2002; Morrison et al., 2000; Wolkowitz & Reus, 1999). For this
study, subjects provided saliva samples by chewing on swabs provided in individual
centrifugible salivettes (Sarstedt Inc., Newton, NC). The swab was held in the mouth for about
one minute, or until saturated. Polyester swabs were chosen instead of cotton, to allow subjects
to moisten them more easily. The samples were frozen and shipped on dry ice for enzyme
immunoassay to the Clinical Research Center Core Lab, Oregon Health Science University,
Portland, OR.
Preparation, Pre-Measurement, and Travel
A few weeks before the experiment, subject demographic questionnaires were filled in, and
cortisol collection methods were pre-tested. Recruits were told generally what to expect during
the session, and asked to bring a sweater and reading glasses if needed. The experiment was
conducted on the first pre-scheduled date with dry weather and suitably warm temperatures. On
that day, about one hour after breakfast, subjects gathered in the dining hall and pre-treatment
measurements were taken. Subjects were then divided into three groups, but were not told where
any of the groups were going. Two groups traveled in the same facility van about five minutes
to the horticulture garden and adjacent classroom, while the third group went to an activity room
at the facility, after walking around for a few minutes to compensate for the travel component.
Each group was accompanied by a non-participatory facility staff member who was on hand for
physical assistance, and by a trained research assistant who administered the measures.
5
Experimental Session
After arriving at the experimental locations, each group of subjects was seated comfortably
around a table, and each research assistant used a prepared script to administer the scheduled
activities. Activities were intended to occupy time in a neutral manner while allowing subjects
to maintain awareness of their surroundings. One activity asked subjects to observe the
surrounding environment, and to describe it using a semantic differential scale. In another
activity, subjects spent a few minutes looking through photo books of either built or natural
environments, to match the treatment setting. These activities were conducted at a leisurely
pace, and along with a few rest periods and filling in the second set of questionnaires, occupied
the remainder of the session. The second saliva samples were collected, and the subjects were
thanked and returned to their residential facility. The entire process took about two and a half
hours overall, with measurements taken about one and a half hours apart.
Results
One subject who recently had a stroke produced incoherent responses that were discarded. One
subject with a sore tongue was unwilling to repeat the salivary cortisol procedure, and two others
failed to produce enough saliva for a comparison. Tests were scored so that on all instruments,
higher scores represented more favorable outcomes. As treatment conditions had been very
similar, data for the indoor groups were combined. Since this experiment was merely a pilot
study, sampling method was not of great concern. The subjects were not randomly selected from
the population of interest and it is therefore not appropriate to use these data to generalize to a
greater population. Thus, the first and most appropriate analyses compare the improvements in
moods, anxiety, and cortisol levels between the sample group of garden subjects and the sample
group of non-garden subjects. Since generalizations are not made to a greater population in these
first rounds of analyses, no p-values are given. For the interest of the reader, a second round of
analyses were performed as if the sample were indeed randomly selected from the population of
interest. In these analyses, a Wilcoxon Rank Sum test was used to test for differences in the four
dependent variables between garden and non-garden populations, and the p-values are given.
The Wilcoxon Rank Sum test was used because there is not sufficient evidence at present to say
that the distributions of the dependent variables are normal, and because the sample sizes are
very small.
Outcomes
Figures 1 through 4 show the mean improvement in mood, anxiety, and cortisol level for the
sample group of non-garden subjects and the sample group of garden subjects. Measures of
location and spread for the four dependent variables in both groups are given in Tables 1 through
4. As can be seen in these tables and graphs, the distribution of the garden group is shifted
slightly above the distribution in the non-garden for cortisol level improvement, anxiety level
reduction, and negative mood reduction. The distribution of increase in positive mood has
greater spread in the non-garden group than in the garden group, but a similar center, indicating
greater variability in responses when subjects are in a non-garden setting.
6
Figure 1: Means for improvement
in cortisol levels for non-garden
and garden groups.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
non-garden garden
Table 1: Measures of center and spread for improvement in cortisol
levels for non-garden and garden groups.
improvement in cortisol level
8 .2225 .1800 -.16 .56 .22154
6 .5933 .3800 .14 1.36 .45772
14 .3814 .3500 -.16 1.36 .37852
treatment
non-garden
garden
Total
N Mean Median Minimum Maximum
Std.
Deviation
Figure 2: Means for reduction in
anxiety level for non-garden and
garden groups.
0
1
2
3
4
non-garden garden
Table 2: Measures of center and spread for reduction in anxiety
level for non-garden and garden groups.
reduction in anxiety
10 1.500 -2.000 -5.0 17.0 6.9960
6 3.500 .500 -2.0 13.0 6.0249
16 2.250 .000 -5.0 17.0 6.5166
treatment
non-garden
garden
Total
N Mean Median Minimum Maximum
Std.
Deviation
Figure 3: Means for reduction in
negative mood level for non-
garden and garden groups.
0
0.5
1
1.5
2
non-garden garden
Table 3: Measures of center and spread for reduction in negative
mood level for non-garden and garden groups.
reduction in negative mood
10 .400 .000 -5.0 7.0 3.3731
6 1.667 .500 .0 7.0 2.7325
16 .875 .000 -5.0 7.0 3.1172
treatment
non-garden
garden
Total
N Mean Median Minimum Maximum
Std.
Deviation
Figure 4: Means for increase in
positive mood level for non-
garden and garden groups.
-0.4
-0.2
0
0.2
0.4
non-garden garden
Table 4: Measures of center and spread for increase in positive
mood level for non-garden and garden groups.
increase in positive mood
10 -.300 -.500 -8.0 7.0 4.1379
6 .000 .000 -1.0 1.0 .8944
16 -.188 .000 -8.0 7.0 3.2500
treatment
non-garden
garden
Total
N Mean Median Minimum Maximum
Std.
Deviation
7
For the interest of the reader, Wilcoxon Rank sum tests were performed to determine significant
differences in the populations of non-garden subjects and garden subjects treating the data as if
they were a random sample. Table 5 gives the p-values for each test, where all hypotheses were
of the form H
a
: garden level > non-garden level, H
o
: garden level ≤ non-garden level (as a
reminder to the reader, greater levels coincide with improvement in the mood and cortisol and
reduction in anxiety, thus the alternate hypothesis, H
a
, is that there is more improvement in the
garden group), and all α levels are 0.10. As can be seen below, if these data were a random
sample from the populations of garden subjects and non-garden subjects, there would be
sufficient evidence at the α=0.10 level to conclude that the improvement in cortisol levels of
garden subjects is greater than the improvement in cortisol levels of non-garden subjects.
Differences were not significant for the other dependent variables.
Table 5: Improvement after exposure to garden and non-garden environments.
Wilcoxon Rank Sum Tests
a
8 10 10 10
6 6 6 6
.0539
b
.1317 .2811 .3564
non-garden sample size
garden sample size
p-value
change in
salivary
cortisol
change in
anxiety
change in
negative
mood
change in
positive mood
All tests are of the form Ha: garden > non-garden Ho:garden <= non-garden
a.
p-value < 0.10
b.
Discussion
Although only one measure is statistically significant when assuming that the data are a random
sample from the population of interest, the differences between groups are in the hypothesized
direction, and are larger than anticipated for this sample size. The sample distributions of two of
the three psychological outcomes show substantially more positive change for the garden group
(outdoor) than for the combined non-garden groups (indoor). The mean anxiety level was
reduced about twice as much outdoors as indoors (3.50 compared to 1.50). The mean negative
mood level was reduced about four times as much outdoors as indoors (1.67 compared to 0.40).
The mean positive mood level remained constant outdoors while declining slightly indoors: (0.0
compared to –.30). As the study was conducted mid-morning while cortisol levels were
decreasing in the normal circadian cycle, salivary cortisol levels for all but one subject were
reduced during the session. However, the mean cortisol reduction for outdoor subjects was about
two and a half times that of indoor subjects (0.59 ug/dl compared with only 0.22 ug/dl), showing
significantly greater stress reduction in the garden environment. These findings generally agree
with the hypothesis, and with previous findings in other populations showing improved health
outcomes associated with gardens and other nature elements (for an overview, see Ulrich, 1999).
Improvements to Study
Caution is appropriate in drawing inferences from these results, because of the small sample size,
inclusion of only one residential complex, and voluntary selection process. Residents who
8
volunteered were probably more active, healthy, and outgoing than others, but this might also
characterize residents who would be more likely to use garden settings provided at a facility. As
an exploratory field experiment, the study contained procedural flaws which could be avoided in
future studies. Unforeseen circumstances partially undermined the randomness and
representativeness of assignment. As the findings showed more consistent differences between
treatments than between facility types, it seems unlikely that this substantially affected the
results. One source of possible bias derived from the principal investigator functioning as
research assistant for the outdoor group. Although the purpose was to acquire direct experience
with the process and observe the non-verbal behavior of subjects in an outdoor setting, further
studies should use passive observation, if any, to avoid contaminating the blinded aspect of the
study. The fact that the hypothesis was known to the researcher might have contributed in subtle
ways to the greater improvement seen in the outdoor group. However, the prepared script and
rigorously scheduled activities served to reduce this source of bias.
Methods Tested
A primary purpose of the study was to test methods for further research. Except for the travel
component and the need to schedule based on weather conditions, the process was feasible and
fairly convenient, including the saliva collection process. As all groups showed primarily
positive changes on all measures over the course of the experience, it seems likely the prospect
of an “unknown” experience produced mild pre-session anxiety and subsequent relief. This
unintentional mild stressor probably strengthened the study design by testing the restorative
qualities of the different environments. An important aspect of this approach is that it tested the
two environments holistically, with the attendant sensory perceptions intrinsic to both
environments. For example, the movement and fragrance of the air, the variability of light
conditions, the sounds and other cues which indicate the degree of openness of the surroundings,
all tend to be systematically different between indoor and outdoor environments. All these
elements were quite different in the two settings, as a direct function of the natural
unpredictability of being outdoors, compared with the relatively static quality of being indoors.
This approach has the advantage of capturing the environmental experience more entirely, but
does not establish which elements were responsible for the effect, or to what degree. The
perception of natural environment as a unified and multisensory experience is underscored in the
literature on horticultural therapy (McBey, 1985; Messer, 1996; Salamy, 1996), and was
considered of primary importance in this experiment.
Further Research and Application
Future studies might include a second outdoor setting with similar light conditions, but very little
vegetation, to examine whether cortisol reduction is attributable to higher light levels or the
presence of plants. Although light level alone might have been responsible for greater cortisol
reduction in the garden group, it could be argued that substantially brighter light is inherently
characteristic of the outdoor environment, and is seldom encountered indoors due partly to the
energy cost of bright illumination. It should also be noted that brighter light may affect cortisol
differently, depending on time of day (Scheer & Buijs, 1999; Leproult, Colecchia, L’Hermite-
Baleriaux & Van Cauter, 2001). Cortisol level typically follows a predictable circadian rhythm,
and for this reason the present study took saliva samples simultaneously, at approximately the
same time after the previous meal. Additional measures such as blood pressure and core body
temperature would be worth comparing, especially if unobtrusive monitors could be worn
9
throughout the session. A neutral relaxing activity could replace the photo books used in this
study, so all environmental stimuli would be direct rather than secondary. The study design
would be greatly strengthened if subjects were assigned to opposite environmental treatments at
alternating sessions, to serve as their own controls (a crossover design). If subjects and facilities
were randomly selected, results could be generalized to the rest of the population. Overall, the
most unexpected result of the study presented here was finding a significant effect with purely
environmental stimuli over a brief time period, in a very small sample. This suggests the value
of following this pilot with a larger study to see if comparable results would be obtained.
Although this study measured the effects of short-term exposure to nature, it seems plausible that
with repeated experiences, modest short-term effects might accumulate into long-term positive
health benefits. If future studies continue to find tangible health outcomes, the implications for
reassessing the value of plants and garden settings could substantially impact the design of
facilities and therapeutic programs for aging.
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The author gratefully thanks the residents, staff, and administration of Crestview Retirement
Community, Bryan, Texas, for their participation in this project. Paul Beathard and Mike Adams
were especially helpful.
Susan Rodiek is a registered architect with national certification, and teaches architectural
design at Texas A&M University, where she is a Fellow of The Center for Health Systems and
Design. She is registered with the PhD program at the Welsh School of Architecture, Cardiff
University, Wales, U.K. Correspondence should be addressed to: Department of Architecture,
Mail Stop 3137, Texas A&M University, College Station, TX 77843-3137, or rodiek@tamu.edu.
Journal of Therapeutic Horticulture, Volume XIII, 13-21. 2002
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