Open Agriculture. 2017; 2: 1–13
has made it possible to breed and cultivate food crop
species far from their centers of origin, and in some cases
into vastly different climatic zones where they would
not be able to survive on their own without the hand of
humankind. Rice, maize, and wheat, originating from
Vavilovian centers II, III and VII (Figure 1), respectively,
are widely grown and account for 60% of the world’s food
energy intake. While the collection of 600 economically
important crop species seems like a substantial number,
it is thought that the documented edible crop species in
cultivation totals about 7,000 species (Khoshbakht and
Hammer, 2008). Yet, there is another 28,000 cultivated
species that belong to an “amenity horticulture” grouping
of plants connected with gardening and landscaping
(Khoshbakht and Hammer, 2008). In contrast to the
important food crop plants with origins from the Vavilovian
centers, amenity horticulture species associated with
landscaping and gardening originate from a much wider
geographic distribution (Figure 1).
We understand the reason for the cultivation of food
crop species, for the energy and essential nutrients they
provide, but what about those in the amenity horticulture
grouping? Is it the aesthetic or other desired sensory
characteristics, or is there something more that underlies
why 80% of the cultivated species have little or no food
related purpose? A growing body of empirical evidence
suggests that plants provide additional health benefits,
over and above that of providing nutrition, consuming
carbon dioxide, generating oxygen, and reducing
airborne particulate pollutants. Besides serving as a main
food source and as an ecological bioregenerative system,
research continues to demonstrate that interactions with
plants provide essential benefits to the health, well-being
and longevity of people, wherever they may live. It is a
given that plants will serve multiple roles in long-duration
spaceflight as people journey ever further from the
Vavilovian centers of crop origin.
DOI 10.1515/opag-2017-0001
Received December 27, 2016; accepted January 9, 2017
Abstract: Plants provide people with vital resources
necessary to sustain life. Nutrition, vitamins, calories,
oxygen, fuel, and medicinal phytochemicals are just a
few of the life-supporting plant products, but does our
relationship with plants transcend these physical and
biochemical products? This review synthesizes some of
the extant literature on people-plant interactions, and
relates key findings relevant to space exploration and the
psychosocial and neurocognitive benefits of plants and
nature in daily life. Here, a case is made in support of
utilizing plant-mediated therapeutic benefits to mitigate
potential psychosocial and neurocognitive decrements
associated with long-duration space missions, especially
for missions that seek to explore increasingly distant
places where ground-based support is limited.
Keywords: Bioregenerative, Cognition, Countermeasure,
Food Crop, Horticultural Therapy, Mental Health, Nature,
Natural Environment, Psychological Stress, Spaceflight
Introduction
Since Mesolithic times wherever people have journeyed,
they have taken their food and favorite plants with them.
By the 20th Century it was realized that most of the 600
economically important cultivated crop plants hail from
eight Vavilovian geographical centers of origin (Vavilov,
1926; 1935; 1992), representing a small percentage of the
total land area of the world. Yet, modern agriculture
Bioregenerative Life Support
It was realized early in the space program that extended
manned exploration of space would ultimately require
farming to support human needs during long-duration
space missions (LDSMs) and the colonization of the Moon
and Mars. Stowage of enough food was never seen as a
viable option for LDSMs. Therefore, Earth-based farming
would need to be adapted to meet the requirements of spacebased
farming (Wheeler and Tibbitts 1987; Wheeler et al.,
1996a, b; Porterfield et al., 2003; Monje et al., 2003; Poulet
et al., 2016). Russian, European, and American scientists
were initially concerned with the influence of spaceflight
conditions on basic plant growth and development,
thus a number of different plant growth systems and
environments that would serve as platforms for basic
plant biology studies and plant cultivation systems were
developed (Ferl et al., 2002; Porterfield et al., 2003; Paul
et al., 2013; Zabel et al., 2016). Over time, improvements
were made to the plant growth systems. However, it
became clear there were physical limitations and physical
chemical challenges to overcome for successful growth of
plants and ultimately for space farming in a microgravity
spaceflight environment (Monje et al., 2003). For example,
microgravity leading to changes in buoyancy dependent
convective transport, increased size of boundary layers
and reduced mass transport posed particular challenges
for plant growth (Monje et al., 2003). Additionally, manned
spaceflight environments were prone to highly elevated
CO2
concentrations (Wheeler et al., 1993; Monje et al.,
2003; Law et al., 2010) and generation of volatile organic
compounds such as ethylene that had unfavorable plant
growth regulating properties necessitating their scrubbing
from the atmosphere (Campbell et al., 2001). Currently, the
Veggie growth system is in operation on the International
Space Station (ISS) and represents the latest version of a
spaceflight food production platform (Massa et al., 2016).
Figure 1. Thirteen regions of origin of ornamental species superimposed over Vavilov’s original eight geographic centers of origin of
cultivated food and economically important crop species (Vavilov 1926; 1935; 1992). The 13 regions are delineated with dashed lines and
filled with different shades of green for clarity of distinction. The 13 regions of origin of over 4,500 ornamental plants were developed by
researchers at Missouri Botanical Garden, and are similar and overlap the twelve mega centers of cultivated plants described by Zeven and
Zhukovsky (1975) for cultivated plants excluding ornamentals, forest trees, and lower plants. (http://www.mobot.org/MOBOT/Research/
russia/origin.shtml)
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Gardening for Therapeutic People-Plant Interactions during Long-Duration Space Missions 3
On Earth, plants perform a number of bioregenerative
ecosystem services, and since the beginning of space
exploration, bioregenerative life support systems were
thought to be essential for LDSMs (Nichiporovich,
1969; Blüm et al., 1994; Mitchell, 1994; Ferl et al., 2002;
Porterfield et al., 2003). Human LDSMs and voyages
require uninterrupted supplies of oxygen, water and food.
Bioregenerative food systems are intended to provide
not only fresh foods (Perchonok et al., 2012), but at the
same time consume carbon dioxide, produce oxygen, and
repurpose grey water for crop growth and conversion to
water vapor upon passing through and out of the plants.
These plant functions are at the heart of embarking on
LDSMs and ultimately colonizing the Moon and Mars.
Programs like NASA’s controlled ecological life-support
system (CELSS) were focused on the goal of developing a
plant-based food supply that would be independent from
the need for resupply from Earth (MacElroy and Bredt,
1984; Mitchell 1994). Therefore, LDSMs would depend
on meeting crew needs for oxygen, water and food, and
maintaining lower ambient carbon dioxide concentrations
with the challenges of limited available power and
volume. An additional function of bioregenerative food
production besides meeting the nutritional needs of the
astronauts would be to help maintain their psychological
well-being, cognitive performance, and crew cohesiveness
and performance. This benefit of the bioregenerative
life support system has long been appreciated as a
countermeasure to the stressful conditions within the
built, confined and isolated environment of a spaceflight
vehicle (Neichitailo and Mashinski, 1993; Mitchell, 1994;
Ferl et al.; 2002, Porterfield et al.; 2003; Bates et al., 2009;
Perchonok et al., 2012), but has received virtually no
formal experimental attention.
Spaceflight and Stress
Living in a spacecraft for extended periods is foreign
to the life most live on Earth. A spacecraft has several
defining characteristics in addition to the absence of
gravity and natural diurnal cycles that make long-term
habitation difficult, particularly with respect for: 1,
isolation; 2, confinement; 3, proximity to a dangerous
hostile environment; and 4, lacking a natural biophilic
interior environment. On LDSMs the crew is cutoff from
direct face-to-face and interpersonal contact with family,
friends, and home that electronic video conferencing
cannot fully substitute. Spaceflight will also continue
for some time into the future to be a continuously risky
endeavor where malfunction or accident could potentially
be an existential emergency. Physical and emotional
challenges can be magnified in a confined environment.
Spaceflight vehicles provide very little physical space that
therefore limits space for movement, space from people,
space for privacy, space from work, space to get away, and
space to work through one’s problems (Shepanek, 2005).
On Earth, confinements are almost always a punishment,
go to your room, go to jail, go to solitary confinement,
and are intended to be unpleasant and stressful for the
purpose of modifying behavior. The smaller the space of
confinement, the greater the unpleasantness and stress of
the experience is likely to be.
Psychological stress can be a function and outcome of
the magnitude of perceived risk and danger. Our species
evolved in a natural world, not in an unnatural man-made
built environment. A simulated interplanetary mission to
Mars study of six men in an analog environment revealed
a diversity of behavioral responses (Basner et al., 2014)
with some individuals exhibiting very modest changes,
and at least one individual with increasingly more severe
behavioral health decrement over time. As we evolved in
a 1g world, living in a microgravity environment poses
physiological and physical health challenges for flight
crews that can negatively impact psychological wellbeing
such as space motion sickness, shifts in body fluid
distribution, and vestibular dysfunction (Williams et al.,
2009). Furthermore, if E.O. Wilson’s Biophilia Hypothesis
is true (Wilson, 1984), then people have an “innate
tendency to focus on life and lifelike processes,” and in a
broader sense this could be taken to mean we have evolved
with an innate need to be in and experience nature. When
these and other factors are taken into consideration, it
seems reasonable that spaceflight and longer duration
space missions could lead to occurrences of mental health
disorders and lower cognitive performance of flight crews
that could imperil crew cohesiveness, command structure,
decision making and ultimately imperil the mission
and safety of the crew. Based on post-mission medical
interviews and examinations, anxiety and annoyance were
the most frequent behavioral symptoms for astronauts
from space shuttle missions (Shepanek, 2005). Other
behavioral issues reported from spaceflight missions
included sleep disorders, reduced energy, attentiveness,
and problem solving ability, memory impairment, and
increased hostility, boredom, and impulsivity. Palinkas
(2001) has reviewed psychosocial issues and concerns
related to the psychological and physical characteristics
associated with LDSM.
NASA has conducted an Evidence Report (Slack
et al., 2015) that evaluated anticipated risks of cognitive,
behavioral and psychiatric disorders during LDSMs. Using
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4 R. Odeh, C.L. Guy
evidence gathered from reports of previous spaceflights
and ground-based spaceflight simulations, estimates
were made on the probabilities of behavioral problems
occurring during LDSMs. The report lays out plans to cope
with inflight mental health disorders through a series of
countermeasures. Inflight countermeasures that relate
to this article include: 7) Interior Design (pages 51-52)
that will provide a richer sensory environment that is
intended to reduce attention fatigue and stress, promote
learning, restoration, and engagement in therapeutic
interventions; and 8) Leisure Activities (page 52) that
engage crewmembers during their time off (Slack et al.,
2015). While space vehicles will always be highly limited
on available interior space, it is suggested that plants will
be included as both a food source and as a therapeutic
countermeasure. Nature is also recognized as being
restorative, but space limitations will probably allow only
simulated nature experiences.
People and Plants
Plants have been a part of the human condition
throughout the last two million years, and their role in our
evolution, cognitive development and survival supersedes
that of all other macro-organisms on the planet. Given our
unqualified dependence on plants for so many everyday
needs, even in today’s world, it becomes unimaginable to
think of what life might hold for us in a world totally devoid
of plants. Plants permeate all aspects of our lives, including
life-supporting oxygen generation and carbon dioxide
consumption, solar energy capture, biological chemical
transformation, sustenance and supply of calories,
vitamins, essential nutrients and minerals, provision
of shelter and production of medicinal compounds; all
the while serving as defining elements of home, culture,
family and our intrinsic well-being. We know plants like
we know the members of family; some we know intimately,
and others we know only distantly. Like family, plants
make us happy, cheerful, fulfilled, comfortable, relaxed,
at ease, secure, composed, peaceful, friendly, and social
(Kaplan, 1995; Frumkin, 2001; Gonzalez et al., 2011a,
b; Kotozaki et al., 2015). In a small adjustment to E.O.
Wilson’s Biophilia Hypothesis (1984), where he states that
Biophilia is: “the innate tendency to focus on life and lifelike
processes” it is suggested here that Biophilia includes:
“the innate tendency to focus on [plants] and [plantlike]
processes, and the apparent evidence of that envelops us
in daily life (Lewis, 1996). Plants provide us with food,
and increasingly science is showing that plants are vital
to our behavioral health and overall well-being (Ulrich,
1986; Ulrich et al., 1991; Gonzalez et al., 2011a, b; Gonzalez
and Kirkevold, 2013; Jo et al., 2013; Bratman et al., 2015;
Kotozaki et al., 2015). This article seeks to make the case
that for long-duration spaceflights and extraterrestrial
habitation; plants will extend ecosystem services to flight
and habitat crews beyond recycling resources and meeting
nutritional needs, to that of sustaining behavioral health,
cognitive performance and overall physical health.
People-Plant Interactions Context
and Background
Perhaps it is of value to begin with the obvious. Why do
tens of millions of Americans engage in some form of
gardening-like or plant care leisure activity, representing
about 70% of all households in the U.S. (Butterfield,
2009)? If one asks gardeners, common replies include,
because gardening makes them feel better, relaxed, less
stressed, happy, at peace, and proud of meaningful work.
Furthermore, the massive body of anecdotal evidence
for the therapeutic benefits of gardening seems too
overwhelming and compelling to not have a biological
basis in reality. The notion that physical work in a garden
offered mental health benefits was first recognized by Dr.
Benjamin Rush in his 1812 book, Medical Inquiries and
Observations, Upon the Diseases of the Mind. Additionally,
Ashton-Shaeffer and Constant (2005) did a survey of 303
older adults, and identified seven motivational factors of
why they engaged in gardening: intellectual engagement,
stimulus-avoidance, friendship building, social
interaction, physical fitness, skill-development, and
creativity. A study by Clayton (2007) examining gardening
and connections to nature found that for a population of
mostly women spending time outdoors, observing nature,
finding relaxation, having pride of effort, and using new
plants were motivations for their gardening activities.
More than 40 years ago, Rachel Kaplan suggested that
gardening would be a good starting point to understand
the psychological benefits of nature experiences
(Kaplan, 1973). She suggested that gardening as a source
of “fascination” could prompt “involuntary attention”
(where involuntary attention is not under the control
of the individual, and occurs when the conscious mind
shifts focus in response to sudden and important changes
in stimulus from the environment, and is less concerned
with motives, interests, needs and functional factors) that
allows the capacity for “directed attention” to be restored.
Directed attention is the voluntary allocation of attention
that can be focused selectively in a sustained way to
specific information or cognitive processes. In the decades
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Gardening for Therapeutic People-Plant Interactions during Long-Duration Space Missions 5
since the Kaplan study, thousands of studies on the
therapeutic benefits of gardening, horticultural therapy,
and nature experiences have been published. The majority
of the literature on gardening and horticultural therapy is
observational and subjective, and does little to advance
understanding of the mechanisms for the therapeutic
benefits of gardening. However, a growing number of
quantitative studies involving diverse populations and
a host of different gardening and horticultural activities
have, in general, reported improvements in mental health
status of study subjects (Clatworthy et al., 2013). More
specifically, studies have reported reductions in anxiety
(Lee et al., 2004; Kam and Siu, 2010; Gonzalez et al.,
2011b), depression (Gonzalez et al., 2011a; Wilson and
Christensen, 2011), negative mood state (Wichrowski et al.,
2005; Kam and Siu, 2010; Van Den Berg and Custers, 2011),
and perceived stress (Kam and Siu, 2010; Yun and Choi,
2010; Kotozaki et al 2015). As foreseen by Kaplan in her
seminal study (1973), interactions with or immersion in
nature and natural areas can similarly lead to reductions in
anxiety, depression, mood state disorders, and perceived
stress, as well as improvements in self-esteem, directed
attention, and cognition (Berman et al., 2008; Annerstedt
and Wahrborg, 2011; Coon et al., 2011; Keniger et al.,
2013). A recent meta-analysis of 25 studies on the health
benefits of exposure to nature found consistent evidence
for positive changes for feelings of energy, anxiety, anger,
fatigue, and sadness (Bowler et al., 2010).
Theories for the Therapeutic
Benefits of Gardening and Exposure
to Nature and Natural Environments
Throughout human evolution there has been an intimate
relationship with nature. One theory posits that directed
attention functions in information processing, and its
use leads to mental fatigue. Rachel and Stephen Kaplan
proposed a framework to explain the apparent restorative
benefits of nature on mental health and cognition (Kaplan
and Kaplan, 1989) that has become known as Attention
Restoration Theory. They postulated that prolonged
directed attention requires cognitive or mental effort
in order to remain focused on a task and ignore outside
distractions. This directed effort leads to mental fatigue.
They used the term “fascination” as a central component or
attribute of nature as a restorative experience. Fascination
or involuntary attention allows individuals to be drawn
into nature and “get away”, even if only conceptually, and
allows directed attention capacity to be restored. In one
form, soft fascination occurs when moderate intensity
activities or experiences can focus a person’s attention that
allows for the continuance of reflection and cognition. A
natural environment is a space where its inherent content
and features serve to provide fascination that promotes
effortless attention. This, in turn, allows depleted directed
attention to be restored (Berman et al., 2008). In this way
nature enhances cognitive functions, while reducing
negative mood state and promoting positive emotions.
Similarly, physiological stress is also seen as being a
factor in depleting mental resources that can be restored
in a fascination-rich environment (Kaplan, 1995). This, in
part, is why nature experiences can be restorative.
Similarly, Ulrich’s Psycho-evolutionary Theory of
stress restoration encompasses an integration of aesthetic
and affective responses to a natural environment,
suggesting that the healing power of nature is, in part,
an unconscious, autonomic response to natural elements
that can happen without conscious awareness and, most
notably, in individuals under physiological stress prior
to a nature experience or even to a perceived simulation
of nature (Ulrich, 1979; 1981; 1983; Ulrich et al., 1991).
Psycho-evolutionary Theory suggests the restorative
powers of nature are associated with being in a familiar
and safe space. Distinguishing a place as being familiar
and safe reduces and relieves feelings of physiological
stress and enhances positive affect. This response is
thought to be an evolutionary characteristic that favored
survival over the course of human evolution. Studies by
Ulrich (1979; 1981; 1983) and other studies provided early
support for the healing powers of nature as suggested by
Ulrich’s Psycho-evolutionary Theory (Ulrich, 1986; Ulrich
et al., 1991).
A recent systematic and comprehensive metaanalysis
of 31 studies regarding Attention Restoration
Theory revealed evidence supporting the theory (Ohly
et al., 2016). This meta-analysis utilized study quality
indicator tools (Centre for Reviews and Dissemination,
2009; Critical Appraisal Skills Programme, 2013; Effective
Public Health Practice Project, 2013) to identify sources of
bias and estimate the robustness of the individual studies.
Quality scores for the studies ranged from 22.5 to 75% with
seven rated as high quality, 22 rated as moderate quality,
and two rated as low quality. A number of assessment
tools were used in the studies to evaluate attention-related
parameters. The Digit Span Forward (DSF) test was used in
five studies and the meta-analysis indicated that natural
These analysts predict marijuana pushing back the total value of the famous “davidfraymusic.com purchase viagra online”, that is currently receiving great reviews and feed back. Its chief constituents are shatavari, saffron, sudh shilajit, moti bhasma, kesar and Safed Musli. buy female viagra We get them checked by a veterinarian regularly and dutifully give them the required medications – be it for pain, sickness, allergy, deworming or even digestive tract cheapest cialis uk motion. Many commander levitra davidfraymusic.com people who suffer from muscle pain have found that they injure themselves because they add more work to the already tired back muscles by lifting and carrying things improperly. environment exposure groups performed better than
controls. The Digit Span Backward (DSB) test was used in
11 studies, and the analysis also indicated that the natural
environment exposure groups performed better than the
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6 R. Odeh, C.L. Guy
controls. Five studies, all by the same research group used
the Search and Memory Task (SMT) for percentage errors
and number of letters searched. There was no difference
between the control and nature treatment groups for the
percentage error rate, but the control groups performed
significantly better than the treatment groups on the
number of letters searched. The Trail Making Test B
(TMTB) was used in three studies and the analysis showed
that the natural environment group performed better than
the control group. This meta-analysis while much more
robust than most conducted in the area of people and
nature and people-plant interactions revealed the need
for more studies that utilize the same set of assessment
tools that are widely agreed upon to evaluate how nature
influences attention and cognitive abilities such as
working memory.
Another recent meta-analysis has focused on studies
dealing with influence of nature on positive affect which
would provide empirical evidence in support of Ulrich’s
Psycho-evolutionary Theory (McMahan and Estes, 2015).
The Psycho-evolutionary Theory suggests that nature
provides a familiar and safe place thereby reducing and
relieving feelings of stress and improving positive affect.
This meta-analysis included 32 studies. Despite there
being considerable heterogeneity in the experimental
designs and methods of the individual studies, the findings
of the meta-analysis suggest that exposure to natural
environments did result in moderate improvements in
positive affect along with a smaller reduction in negative
affect relative to control groups. McMahan and Estes
(2015) also examined whether there was a difference
in responses to actual nature experience or simulated
nature such as viewing photographs of nature. They
found larger effect sizes in response to real nature as
compared to that of simulations of nature. Therefore,
while viewing simulations of nature can improve positive
affect, actual nature experience appears to have a greater
ability to improve positive affect. These overall results can
be viewed as support for Ulrich’s Psycho-evolutionary
Theory for the restorative powers of nature experiences.
Behavioral and Cognitive Benefits
of Gardening
Behavioral and cognitive effects of LDSM conditions
based on isolated, confined and extreme (ICE) analog
environments and psychological assessments of
astronauts on longer duration Space Shuttle flights and
missions to the various space stations including Salyut,
Mir and ISS have been informative, and demonstrate
increased likelihood of mental health disturbances
(Sandal et al., 2006; Paulus et al., 2009). Given the goal
of reaching Mars, psychological issues are expected
to be exacerbated with the decrease in ground-based
therapeutic interventions that are now possible in current
low Earth orbit missions. Therefore, space farming or
gardening may offer a treatment modality that reduces
the decline of crew mental health and well-being. A
rigorous critical assessment of the evidence-based
research on gardening as a mental health intervention
was conducted by Clatworthy and colleagues for the
years 2003-2013 (Clatworthy et al., 2013). From a list of 156
references produced by systematic search, just ten studies
met four standards: 1, providing an empirical evaluation
of an intervention involving active gardening; 2, adult
participants experiencing functional mental health
difficulties; 3, published in a peer-reviewed journal; and
4, written in English (Son et al., 2004; Stepney and Davis,
2004; Parr, 2007; Rappe et al., 2008; Gonzalez et al.,
2009; 2010; 2011a; b; Kam and Siu, 2010; Parkinson et al.,
2011). Based on quantitative psychometric assessments,
seven of the studies reported statistically significant
reductions in depression, four showed reductions in
anxiety, two found increased attentional capacity, and
one reported increased self-esteem. Qualitatively, three
studies found reductions in stress and improved mood,
and two recorded improved social skills. An earlier critical
assessment of studies on the benefits from gardening
for adults with mental health difficulties by Sempik
and colleagues (2003) identified as few as five studies
that were experimentally sound. As a further example,
a search for randomized controlled trials involving
horticultural therapy by Kamioka and colleagues (2014)
returned only four studies. Two of the studies reported
improvements in depression symptomatology (Kim et al.,
2003; Kam and Siu, 2010). A more recent series of studies
by Kotozaki and colleagues (Kotozaki, 2013a; b; 2014a; b;
c; Kotozaki et al., 2015) focused on women suffering from
PTSD from the Great East Japan Earthquake of 2011 have
provided additional empirical evidence for the benefits of
gardening or horticultural therapy. Taken together, these
studies have shown gardening-based experimentally
controlled horticultural therapy interventions result in
statistically significant improvements in positive affect,
total mood disturbance, quality of life as well as reductions
in clinician-administered PTSD Scale scores and salivary
cortisol levels. Further conclusions drawn from a number
of retrospective studies and reviews concerning the
mental health benefits of gardening identify the paucity
of sound empirical evidence as a prevailing problem, and
underlines the need for more high quality research.
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Gardening for Therapeutic People-Plant Interactions during Long-Duration Space Missions 7
Social Benefits of Plants
With the associated challenges of long-duration
spaceflight, including isolated, confined and extreme
environmental conditions, astronauts are at risk for
interpersonal issues with their flight crew members and
ground-based control. Other factors affecting cohesion of
crew members are faulty leadership and cultural barriers
(Kanas et al., 2001; Bates et al., 2009). Such interpersonal
conflicts could lead to a number of undesirable group
dynamics such as decreased trust, cooperation,
productivity and safety. Furthermore, interpersonal
conflicts could lead to a number of negative behaviors
associated with sleep, attention, anxiety, depression,
substance use, stress, and rumination. Interacting with
plants and accessing plant-rich environments have been
correlated to enhanced social integration, group cohesion
and social functioning (Cho and Mattson, 2004; Son et al.,
2004; Gonzalez et al., 2011b). In one study, inner-city
participants reported an enhanced sense of safety and
preference associated with more green space (Kuo et al.,
1998). In a study conducted by Kuo and Sullivan (2001),
increased plant density was correlated with decreased
crime rates, violence, aggressiveness and residents’ fear
in an inner-city community. Qualitative studies indicate
community garden efforts can encourage positive social
behaviors (Waliczek et al., 1996) and promote cultural
and/or racial social interactions (Shinew et al., 2004;
Wakefield et al., 2007). Taken together, these studies point
to horticultural activities as a way to build social union
and dismantle social tensions; benefits which could be
especially valuable to flight crews under ICE conditions
during LDSMs.
Psychological Benefits of Indoor
Plants
Plants are commonplace in homes, the workplace, and
public indoor spaces like lobbies, atriums, waiting
rooms, and shopping malls, but plants have commonly
been kept in their own isolated and confined boxes
during spaceflight. In some cases, flight crews have
been able to more closely interact with plants and have
been able to cultivate and care for them. Plants are
brought indoors for many different reasons, including
enjoyment, aesthetics, interiorscaping, and for healthrelated
benefits. For decades, indoor plants have been
touted for their health and therapeutic benefits. A critical
analysis of the peer-reviewed, published experimental
literature on the behavioral effects including cognition,
affect, and physiology that indoor plants passively
provide to occupants was conducted by Bringslimark
and colleagues (2009). Following a systematic literature
search, 21 studies were selected for analysis. Overall, the
results for psychological benefits were found to be mixed.
Reasons for different outcomes among studies included
experimental diversity and lack of standard methods in
settings, experimental design, treatments, number and
types of plants, exposure durations, types of samples,
and measurement methods, small magnitude of effects,
and lack of sufficient power to detect treatment effects.
The most consistent findings of benefit were reduced pain
and anxiety following surgery (Park et al., 2004; Park and
Mattson, 2008; 2009), and higher pain tolerance (Lohr
and Pearson-Mims, 2000).
Influence of Nature and Gardening
on Patterns of Brain Activation
Studies are emerging that couple neuroimaging with
nature experiences or gardening for therapeutic purposes
in an effort to link changes in behavioral health with
patterns of brain activation. A recent study found that
images of the sky produced activations in the same regions
of the brain as other positive stimuli (Pati et al., 2014). Two
studies looked at the patterns of brain activation upon
viewing images of landscapes compared against neutral
versus ugly stimuli, or outdoor versus indoor images
(Kawabata and Zeki, 2004; Henderson et al., 2007). Both
studies reported differential activation patterns suggesting
that the brain responds differently to outdoor and natural
landscapes. The first study to examine changes in the
patterns of brain activation resulting from a horticultural
therapy intervention was conducted on a group of five
individuals recovering from cerebrovascular disease
(Mizuno-Matsumoto et al., 2008). Unfortunately, the study
is highly suspect due to the small sample size and overall
weak experimental design. Two other studies published in
2015 offer a stronger connection of neurological changes
and patterns of activation with gardening and nature.
Following an 8-week horticultural therapy intervention,
women suffering from PTSD resulting from the 2011
Earthquake in Japan had increased regional gray matter
volume of the left subgenual anterior cingulate cortex
and left superior frontal gyrus compared to the control
groups that received an 8-week educational intervention
(Kotozaki et al., 2015). These two regions of the brain are
associated with mood disorders and depression (Drevets
et al., 2008), and cognitive functions, particularly working
memory (Du Boisgueheneuc et al., 2006). Another study
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8 R. Odeh, C.L. Guy
contrasting the levels of rumination before and after
walking through a nature or urban setting for 90 minutes
measured reduced rumination for the participants taking
the nature walk, but no change for those taking the urban
walk. Using arterial spin labeling magnetic resonance
imaging, cerebral blood flow was quantified. Regional
blood flow decreased in the subgenual prefontal cortex
for nature walk participants only, suggesting reduced
neural activity. This region of the brain has been linked
to increased activation associated with higher levels of
rumination. Participants taking the urban walk did not
show a reduction of cerebral blood flow or decreases in
rumination (Bratman et al., 2015). More scholarly work
in the area of brain activation is necessary to unveil a
clearer understanding of the linkages between these
patterns of brain activity, behavioral health, and nature
and gardening.
Anecdotes from Astronauts on
People-Plant Interactions in Space
“Pleasure for one hour, a bottle of wine. Pleasure for one year,
a marriage; but pleasure for a lifetime, a garden.”
Chinese Proverb
Growing plants in space could provide salads and other
foods for future space crews, but they also may bring
other psychological and biological benefits. Perhaps the
first indication of the psychological impact of growing
plants in space was expressed by Cosmonaut Valentin
Lebedev (1990) in his diary during spaceflight where he
wrote: “Our “farms” in the Oazis, Fiton, and Svetoblock,
where we cultivated plants, are empty now.” Lebedev
later recorded that: “During a TV broadcast we admitted
that we feel sad and uncomfortable without our garden
and without our dear plants. It was such a pleasure to
take care of them. Man probably has a need to take care
of things and without those things feels empty.” Similarly,
when she first saw the growing soybeans in the Advanced
AstrocultureTM (ADVASC) Experiment hardware on the ISS
(Figure 2), Peggy Whitson, an Iowa native, reported in an
e-mail letter home to family and friends: “It was surprising
to me how great 6 soybean plants looked.” She also wrote:
“I guess seeing something green for the first time in a
month and a half had a real effect. From a psychological
perspective, I think it’s interesting that the reaction was as
dramatic as it was.” Whitson went on to write: “guess if
we go to Mars, we need a garden!.” Astronaut Don Pettit
provided compelling anecdotal evidence and support for
plants in space in blogs and other resources, where he
affectionately described his interaction with a zucchini
plant. In one of his blogs, taking on the persona of the
zucchini, Pettit wrote about his experience with the
zucchini: “Apparently he takes pleasure in my earthy green
smell. There is nothing like the smell of living green in
this forest of engineered machinery.” More recently Scott
Kelly’s Tweet on January 16, 2016 of the: “First ever flower
grown in space makes its debut!”1 was picked up by the
media and generated worldwide interest. Kelly took over
care of zinnia plants that were being grown by Astronaut
Kjell Lindren for an experiment in the Veggie plant growth
platform on the ISS (Figure 3). A control cohort of plants
was also being grown on Earth for comparison. In fact,
it was Kelly’s care that salvaged the experiment and
enabled some of the plants to overcome a fungal growth
problem and develop flowers. In an interview with NASA,
Kelly explained: “I think we’ve learned a lot about doing
this kind of experiment. We’re being farmers in space,”
Kelly declared: “I was extra motivated to bring the plants
back to life. I’m going to harvest them on Valentine’s Day.”
(NASA Flowering Zinnias, http://www.nasa.gov/feature/
flowering-zinnias-on-space-station-set-stage-for-deepspace-food-crop-research).
One can speculate why one
zinnia flower on the ISS would be so interesting and such
a big deal to so many people? A Google search of “first
flower in space” returned just under 80 million hits
(searched November 25, 2016). When taken together, the
expressed enthusiasm by astronauts and cosmonauts for
seeing and growing plants in space provide a compelling
justification for quantitative research studies measuring
the impacts that plants have on crew mental health and
well-being under spaceflight conditions. It is appreciated
that in addition to recycling carbon and oxygen, growing
plants in the easily accessible Veggie is recognized as an
opportunity for astronauts to receive the psychological
benefits of growing and caring for plants on the ISS (Vessel
and Russo, 2015).
The zinnia flower experiment is not the first to
attempt to have flowers on an orbital station. The
Malachite device plant growth system on Salyut 6 was
used for an experiment with the purpose of growing
ornamental plants. The idea in this experiment was to
provide psychological benefits for the cosmonauts on the
space station. The plant growth system had four boxes
with a water supply and lighting to support plant life.
Orchids were chosen to be sent into space bearing flower
blossoms (Neichitailo and Mashinski, 1993, Porterfield
1 Scott Kelly’s Tweet was incorrect as a number of different plants
had flowered in space on several occasions over the previous 30
years of manned spaceflight.
Unauthenticated
Download Date | 10/19/17 5:07 PM
Gardening for Therapeutic People-Plant Interactions during Long-Duration Space Missions 9
Figure 2. Flight engineer Peggy Whitson was pleased to show soybean plants growing in the Advanced AstrocultureTM (ADVASC) Experiment
hardware on the ISS on July 10, 2002. The hardware provided precise control of light, temperature, fluid nutrient delivery, relative humidity,
carbon dioxide (CO2
) and ethylene concentrations. An agricultural seed company grew the soybeans in the ADVASC hardware to determine
if soybean plants could go from seed to seed in a microgravity environment. Secondary objectives included determination of the chemical
composition of the seeds grown in space and whether microgravity had an impact on the plant growth cycle. Image catalogued by Marshall
Space Flight Center of the United States National Aeronautics and Space Administration (NASA) Photo ID: MSFC-75-SA-4105-2C. Image
credit: NASA https://mix.msfc.nasa.gov/abstracts.php?p=2393
Figure 3. Zinnia plants in flower in the Veggie plant growth system onboard the International Space Station on January 16, 2016. Plants
were grown from November 16, 2016 to the date of the photograph by astronauts Kjell Lindgren and Scott Kelly. Growing zinnias on the ISS
provided an opportunity for the astronauts to practice gardening in space. The first flowers grown from seed in space occurred previously
on Mir, on Salyut-6 in 1982. Russian and American scientists have been conducting plant research in space since the late 1970’s.
Image catalogued by Johnson Space Center of the United States National Aeronautics and Space Administration (NASA) Photo ID: ISS046-
E-009029. Image credit: NASA https://upload.wikimedia.org/wikipedia/commons/f/fd/ISS-46_Zinnia_flowers_in_the_Veggie_facility_%283%29.jpg
Unauthenticated
Download Date | 10/19/17 5:07 PM
10 R. Odeh, C.L. Guy
et al., 2003). Cosmonauts Popov and Ryumin in 1980
found that the orchids grew normally for 177 days but
they didn’t flower. Several in-bloom orchids that were
carried to the space station quickly faded and lost all their
blossoms within 2-3 days of arrival in orbit. Orchids were
chosen for the experiment, because they don’t always
grow upwards on Earth. While these anecdotes do not
provide direct experimental evidence in support of the
psychological benefits of growing plants in space, they do
show the affective responses and high level of interest by
the astronauts associated with having greenery on board
space vessels.
Gaps and Countermeasures
Future studies involving the analysis of plant-mediated
psychosocial factors could address NASA Human
Research Program gaps to identify promoters and
validate model countermeasures that will help to
sustain individual and group psychosocial health and
cognitive performance during LDSMs. At this time, there
is great need for more research in all areas of peopleplant
interactions to better define treatment effect size
responses and understand the true impacts that nature
and plants have on human well-being. Interestingly,
research implementing plants in isolated and closed
environments that are characteristic of LDSMs has the
potential to generate extremely important empirical
evidence that presently does not exist in the extant
literature. Results from such studies could lead to more
complete conclusions on the beneficial effects of peopleplant
interactions in ICE environments, specifically
related to psychosocial health, cognitive performance,
and group cohesion. A current weakness in all studies
of the benefits of people-plant interactions, especially
those surrounding the Biophilia Hypothesis context, is
the background influence of the presence of plants in
the daily life of study participants. Moreover, there is
not a good understanding of how long the benefits of a
nature experience or person-plant interaction persist.
Removal of this background or residual influence could
amplify and reveal the magnitude of treatment effect
size emanating from people-plant interactions. At the
present time, analog LDSM ICE environments on Earth
could be used to formally test the true impact of being
in the company of, growing, and enjoying the rewards
plants can provide. This could be accomplished in a true
experimental design with and without plants. It offers the
opportunity to identify a potentially effective, accessible,
and non-pharmacological therapeutic modality to treat
adverse behavioral conditions and psychiatric disorders.
Perhaps more importantly, projects involving plantmediated
therapeutic modalities will contribute to the
identification of an effective method for modifying the
habitat/vehicle environment, specifically during LDSMs,
to mitigate decrement of psychological and behavioral
health due to environmental stressors stemming from
prolonged ICE conditions. This could be accomplished
using assessment instruments and tests that are widely
recognized standards used in the fields of psychology
and neuroscience.
Conclusion
As humankind ventures further away from Earth, our food
and favorite plants will be carried along on the journeys
much further from their Vavilovian centers of origin
than ever before. Taken together, there is a limited, but
a sufficient body of empirical evidence to suggest that
nature and plants, particularly active interactions with
plants through farming and gardening, offer behavioral
health and cognitive function therapeutic benefits.
While there is evidence for these benefits in ambient
Earth-bound environments, we are not aware of a single
study that demonstrates whether or not the therapeutic
benefits would carry over into a spaceflight environment
disconnected from the natural sensory stimulation and
input provided by plants. Determination of the magnitude
of treatment size effects of plants on neurocognitive
functions is a step toward establishing space farming and
active engagement with plants in space as a potentially
effective non-pharmacological countermeasure to
the anticipated decrement of behavioral health and
performance during LDSMs. It is clear that more research
is necessary to arrive at a better understanding of the
mechanisms involved in people-plant interactions on
Earth and in space.