Container gardens: Possibilities and challenges for environmental and social benefits in cities

Abstract

Container gardens are used in cities around the world where access to soil at ground level is limited. They represent artificial ecosystems but often provide the only vegetation in some highly urbanized locations, and have been used in vertical and horizontal forms of living architecture. Although there are many container gardens in urban areas, container gardening as a component of more broadly considered green infrastructure seems to be unappreciated. The aim of this review is to elucidate potential ecosystem services provided by container gardening. The ultimate goal of this review is to recognize the value of container gardens in order to promote them as part of green infrastructure in urban areas. The ecosystem services which container gardens provide were sorted into the following categories (1) Provisioning (food production and security); (2) Regulating (stormwater management, improvement of air quality, energy savings and thermal comfort); (3) Habitat/Supporting (plant biodiversity and creation of animal habitats); (4) Cultural (aesthetic and improvement of visible green ratio, communication and environmental education, material reuse). Container gardens deserve serious attention as a form of urban greening that can provide many direct and indirect benefits to people living in cities. Moreover, it is important for citizens, local authorities and academics to be aware of the ecosystem services associated with container gardening to promote further development of its potential.

Full text

This peer-reviewed article is provided free and open-access.
Volume 8 Number 2 Pages 1-19 2021
Container gardens: Possibilities and challenges for
environmental and social benefits in cities
Ayako Nagase1*, Jeremy Lundholm2
1 Graduate school of global and transdisciplinary studies, Chiba University, Japan
2 Department of Biology, Saint Mary's University, Canada
*corresponding author: anagase@chiba-u.jp
ABSTRACT
Container gardens are used in cities around the world where access to soil at ground level is
limited. They represent artificial ecosystems but often provide the only vegetation in some
highly urbanized locations, and have been used in vertical and horizontal forms of living
architecture. Although there are many container gardens in urban areas, container gardening as
a component of more broadly considered green infrastructure seems to be unappreciated. The
aim of this review is to elucidate potential ecosystem services provided by container gardening.
The ultimate goal of this review is to recognize the value of container gardens in order to
promote them as part of green infrastructure in urban areas. The ecosystem services which
container gardens provide were sorted into the following categories (1) Provisioning (food
production and security); (2) Regulating (stormwater management, improvement of air quality,
energy savings and thermal comfort); (3) Habitat/Supporting (plant biodiversity and creation of
animal habitats); (4) Cultural (aesthetic and improvement of visible green ratio, communication
and environmental education, material reuse). Container gardens deserve serious attention as a
form of urban greening that can provide many direct and indirect benefits to people living in
cities. Moreover, it is important for citizens, local authorities and academics to be aware of the
ecosystem services associated with container gardening to promote further development of its
potential.
Key words: Green infrastructure, biodiversity, communication

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INTRODUCTION
Currently, the human population is rapidly concentrating in urban areas and green
infrastructure is becoming important for societal sustainability (Brzuszek et al., 2007; Davies
and Lafortezza, 2017). Green infrastructure can be defined as “natural, semi-natural, and
artificial networks of multifunctional ecological systems within urban areas” (Tzoulas et al.,
2007). Green infrastructure comprises open areas such as urban forests, large public parks,
gardens, playing fields, rights-of-way along streams and roads, and constructed features such
as green roofs, permeable vegetated surfaces, swales, rain gardens and green streets (Mell et
al., 2013; Tzoulas et al., 2007). Container gardens are an important component of green
infrastructure in many cities.
Container gardens have been used for thousands of years. Carved scenes on limestone walls
of an Egyptian temple, dating back 3,500 years, depict frankincense trees growing in pots
(Manso and Castro-Gomes, 2015). Container gardening is well established in history as a
practical way to replace lost ground space in urban environments (Welch, 2013). They can be
easy to move, allowing seasonal transport of plants indoors to avoid winter or dry-season
conditions. In addition, they are easy to arrange and decorate in three dimensions. Urban
container gardening is often promoted as a solution to lack of space at ground level for
gardens (Bailey, 1993; Choonsingh et al., 2010). Container-based systems are also sometimes
the only form of gardening available in dense cities where soils are largely covered with hard
surfaces, resulting in strong competition for space.
In both private spaces (e.g. around houses, roofs, balconies) and public spaces (e.g. open
spaces and roadsides), container gardens are frequently seen. In heavily built-up areas, both
formal and informal container gardens can be seen. Formal versions of container gardens are
often placed in public lands such as city squares, managed by municipal staff and consist
mainly of ornamental landscape plantings similar to those used in in-ground (growing
directly in the ground) landscaping in public parks (Figure 1d). These can also be found in
corporate and institutional settings, such as courtyards in the urban core, but are similar to
other formal container plantings in that paid staff manage the vegetation according to
organizational standards. In contrast, informal container gardens tend to be more diverse,
driven by the needs and preferences of individual gardeners. They are also generally created
and maintained on an unpaid basis (Figure 1a-Figure 1c).
In general, container gardening can be considered as small mobile versions of living
architecture. Container gardens are frequently used informally at private dwellings whereas
many other kinds of living architecture may be more common in public spaces. While green
roofs and living walls may involve containers for plants and growing media, container
gardening, especially when done by private citizens, often uses much smaller container
formats. This results in high maintenance requirements (e.g. irrigation) but also allows for
high plant diversity within small areas due to owner preference.

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Figure 1 Summary of review. Ecosystem services, case studies and future research are shown. The
pictures are examples of container gardening from different countries (a) Mexico (b) Japan (c) Japan
(d) UK (e) Japan (f) Korea (g) Sweden (h) Canada. All photographs were taken by Ayako Nagase.
Although there are many container gardens in urban areas, container gardening as a
component of more broadly considered green infrastructure seems to be unappreciated. One
of the reasons might be that individual containers are too small to be commonly recognized
as a component of green infrastructure. While individual containers are small, a large amount
of containers may be able to complement other greening initiatives in high density areas.
Container gardens, whether developed by individual citizens as home gardens or
municipalities or corporations as formal urban landscaping, are often part of in-ground
gardens as well. Hence much of the urban gardening literature may include but not mention
specifically the containers that can be a key component of all urban gardens in some regions
(Buchmann 2009). For home gardens, another reason for the lack of attention to container
gardens might be that much of this gardening can be perceived as a recreational activity for
people and is largely unmanaged by local governments, in contrast to other types of green
infrastructure, therefore, in general, they are not treated as seriously. Most of the urban
ecology literature ignores container gardens or lumps them in with conventional ground-level
gardens.
Ecosystem services, conceptualized as benefits from ecosystems to human well-being
(TEEB, 2011) are increasingly acknowledged to ameliorate urban living conditions (Elmqvist
2013; Tzoulas et al., 2007). There has been recent attention to urban gardens from the
perspective of ecosystem services (e.g. Borysiak et al., 2017; Cameron et al., 2012; Goddard

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et al., 2010; Jim and Zhang 2015). Home gardens, community gardens and informal container
gardens represent a “bottom-up” activity and they may contribute to the same ecosystem
services. However, it is necessary to review ecosystem services separately for container
gardening because the uniqueness of container gardening has not been discussed and they
differ from other kinds of gardens in growth conditions, plant selection and mobility. There
has been little review of research on ecosystem services derived from container gardening.
This is the research gap. The aim of this review is to elucidate potential ecosystem services
provided by container gardening. In this paper, containers are defined as vessels for growing
plants with surface areas of substrate generally less than 1 m × 1 m, which may or may not be
fixed in place. They consist of plants, substrate (substrate), the container itself and
occasionally gravel or rocks at the base as a drainage layer. They are maintained and irrigated
regularly and sometimes fertilizer is applied. From previous studies, we classified ecosystem
services which container gardening may provide into these four common ecosystem services
(TEEB, 2011): (1) Provisioning (food production and security); (2) Regulating (stormwater
management, improvement of air quality, energy savings and thermal comfort); (3)
Habitat/Supporting (plant biodiversity and creation of animal habitats); (4) Cultural (aesthetic
and improvement of visible green ratio, communication and environmental education,
material reuse). After summarizing the ecosystem services, we describe international case
studies to address the regional differences in drivers of container gardening adoption. We
then discuss future directions for research in container gardening. The ultimate goal of this
review is to recognize the value of container gardens in order to promote them as part of
green infrastructure in urban areas.
ECOSYSTEM SERVICES
Provisioning Services
Food Production
Currently, interest in urban agriculture is increasing rapidly and people are motivated to grow
vegetables and fruits for food (Figure 1a and Figure 1f). Home gardens can produce a
substantial amount of food in urban areas (CoDyre et al., 2015). Many participants are
activists who wish to promote social change, ensure affordable access to vegetables or
improve health (Kirkpatrick and Davison, 2018). In urban areas, planting in containers or
raised beds on apartment building balconies or roof tops is common in many countries
(Dunnett and Clayden 2007; Nasr et al., 2017; Oh et al., 2018; Vazhacharickal, 2014).
Vegetables are most commonly grown in container food gardens, but many small fruit trees
are also common, especially in the tropics. In some places, apple and pear, and shrubs with
pliant branches are used as espaliers (pruned trees or shrubs trained flat against a wall) in
container gardening (Cantor 2008).
According to studies of container gardens in Singapore, provision of food and medicinal
resources (77.5%), and aesthetic benefits (72.3%) were the key ecosystem services provided
by the plant species present (Oh et al., 2018). Container gardening is used for supplemental
food production in home gardens, but new initiatives are using containers in public or
corporate spaces to host community gardens. One study estimates that 77% of the vegetable

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requirements in Bologna, Italy, could be met if all available rooftops were gardened using
container plantings (Orsini et al., 2014) and food security concerns are driving an expansion
in container gardening globally (Bailey 1993; Buchmann 2009; Gopal and Nagendra 2014).
Preparing for uncertain factors such as natural disasters and climate change is also becoming
important. However, very little published research is available on growing vegetables and
fruits in containers beyond production aspects. There are many popular books for gardeners
that introduce methods for growing vegetables and fruits in containers but scientific studies
are lacking on the effects of growing media composition and depth, cultural practices,
potential water-quality issues of effluent and how food production could influence the other
known benefits attributed to container gardening (Whittinghill and Rowe 2011).
Regulating Services
Stormwater Management
Storm water management is one of the important environmental benefits of green
infrastructure. Traditional urban runoff management strategies rely on channeling rainwater
into city sewer systems, but peak storm events can overwhelm system capacity (Newell et al.,
2013). Since space tends to be limited in urban areas, planters are appropriate for storm water
management. Specifically designed storm water planters are above-ground planting
containers that intercept water. They reduce water runoff through infiltration, evaporation,
transpiration and storage (Dunnett and Clayden 2007). In terms of design, the ability of a
container planting to retain stormwater depends on substrate properties such as porosity,
organic matter content, and antecedent moisture conditions. Some studies on growing media
used in containers show up to two times the variability in soil moisture contents under the
same moisture regimes depending on the kind of media used (Fonteno 1988). The surface
area available and the depth of the substrate are also crucial in determining overall runoff
retention ability.
Although container plantings have been introduced in rain gardens (Ellis 2013; Kuller et al.,
2018), little research documents the benefits of container planting to reduce water runoff and
to improve water quality. While larger catchment areas reduce peak runoff by a greater
amount than smaller areas, with the same substrate depth, studies on small green roof trays or
experimental systems show similar runoff reduction to larger scale green roofs (e.g. Nagase
and Dunnett 2012) so the small area of individual containers should still allow substantial
stormwater retention in urban areas dominated by hard surfaces. Capture and storage of
rainwater in barrels or cisterns is also used to irrigate container gardens in some places, and
this represents a positive benefit that also reduces runoff into urban systems.
Improvement of Air Quality
Container gardens can contribute to improving outdoor air quality. Urban vegetation is
known to trap airborne particles and to take up other contaminants such as nitrogen oxides
(Oberndorfer et al., 2007). Once inside the leaf, gases diffuse into intercellular spaces and
may be absorbed by water films to form acids or react with inner-leaf surfaces (Smith, 2012).
Many studies have shown that trees can contribute to improvement of outdoor air quality,
however, while trees and shrubs are sometimes used in container gardening, studies of the

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impact of herbaceous plants, which are more commonly used in containers, on air quality are
limited. Herbaceous plants can also improve urban air quality (Currie and Bass 2008).
Analysis of leaves harvested from roadside herbaceous vegetation in Berlin showed that
species with the highest particulate matter accumulation rates were ones with hairy or rough
leaves and that leaves 15 cm or higher from the ground collected more particulate matter
(Weber et al., 2014). Herbs with smooth leaves and grasses were found to accumulate less
particulate matter than other plants with hairy leaves. Although herbaceous plants were not
very effective in removing particulates from the air, different herbaceous plant species
captured different sizes and types of particulate matter (Weber et al., 2014). Further research
is necessary to document how plants which are commonly used for container plants can
contribute to the improvement of air quality.
Energy Savings and Thermal Comfort
Container gardens installed adjacent to buildings can contribute to improved energy savings
and thermal comfort in the urban environment. Container plants directly exposed to the sun
intercept solar radiation, cooling local microclimates via reflection and transpiration.
However, in urban areas, the placement of container gardens relative to shade from adjacent
buildings or trees will have a large influence on the degree to which container plants can
influence urban climates. In terms of plant selection, species that tend to be taller and have
greater leaf areas and stomatal conductance rates have higher overall evapotranspiration (ET)
(Fynn et al., 1993; Stanley and Harbaugh 1992), so these should increase microclimatic
cooling but such species may have greater irrigation requirements. Growing media properties
can also influence the thermal performance of container plantings. Soil moisture holding
capacity can result in higher ET (Valdés et al., 2008), and soil amendments including
mycorrhizal inoculation can result in larger plants with greater horizontal cover (Srinath et
al., 2003), leading to greater cooling potential.
The deployment of containers on vertical surfaces may increase the utility of container
gardening for ameliorating climate in hot conditions. Simple green facades using containers,
the so-called “green curtains”, are very popular in Japan, particularly after the Great East
Japan Earthquake in 2011 since awareness of power savings has increased (Okushima et al.,
2014; Suzuki 2012) (Figure 1b). Some local authorities provide plants for green curtains
without charge to promote energy savings. They also organize workshops on how to grow
these plants. Plants which are commonly used for green curtains at home are annuals such as
Momordica charantia var. pavel, Luffa cylindrica and Ipomoea sp. over summer. They
usually expect to reduce building cooling costs over summer, and then they remove them in
the autumn and set up again in the spring. A few studies have been carried out to show how
green curtains reduce summer wall temperatures. One study compared outside surface
temperatures of windows behind different screens of green curtains; the temperature behind a
cheesecloth screen was highest, that behind a reed screen was second, and that behind the
Momordica charantia L. was the lowest (Okushima et al., 2014). However, the plant growth
of green facades using containers may be less than those of which are planted on the ground
because of limited soil volume. Further studies are required to elucidate the relationship
between soil volume and thermal performance.

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Habitat/Supporting Services
Plant Biodiversity and Creation of Animal Habitats
Although there are long lists of recommended plants for container gardens internationally in
books (e.g. Kasahara 2005; Peters et al., 2007; Titchmarsh 2009), little empirical research has
documented what kinds of plants are actually used or preferred for container gardens in
different regions. Some studies provided detailed plant lists for container gardening.
Shinozuka et al. (2002) studied container gardening in Sumida city in Tokyo and they
showed that the plant list can be divided into five broad types of plants: ornamental flower
plants, ornamental leaf plants, ornamental fruit plants, food plants and plants grown for good
luck or other cultural significance ("lucky charm" plants). Many people prefer to keep lucky
charm plants in front of their houses and some of them were originally housewarming gifts
when they moved in (Figure 1e). In another study, Oh et al. (2018) studied the (outdoor)
corridors of apartment buildings in Singapore, and showed that across 1.86 ha of surveyed
corridors a total of 265 plant species and cultivars were present in the containers, with an
average richness of 124 species per hectare. They also showed that 10.4% of plants were
natives, including some rare native species, and 82.2% were exotics. Jonas (2007) studied
container gardening in Tsukishima in Tokyo and showed that most of the plants are around
20-100 cm tall, and the usual diversity combines 3-10 species such as Azalea spp., Amaryllis
spp., Camelia spp., Cyclamen spp., Fuchsia spp., Hibiscus spp., Hydrangea spp., Mimosa
spp., Nerium oleander, Schefflera spp., Viola spp., Yucca spp. Matsuo (1977) studied
container gardens in Kagoshima city, Japan and found that about 260 plant species were
observed and 70 % of them were ornamental plants. Container gardens can contain a high
number of plant species within a small area.
Many studies have been carried out to show that domestic gardens can contribute biodiversity
benefits (Goddard et al., 2010). There are limitations, however, to the ability of constructed
ecosystems to supply biodiversity benefits in urban areas: relative isolation from green
spaces, the presence of non-native species, novel ecological conditions and stressful
environments (Williams et al., 2014) may reduce the ability of container gardens to support
biodiversity conservation aims. Given the small relative area of container gardens, it is likely
that they may provide habitat primarily for generalist species that are already successful in
urban environments (Cameron et al., 2012; Williams et al., 2014). Birds have also been
reported to use container gardens (Oh et al., 2018).
Cultural Services
Aesthetics and Improvement of Visible Green Ratio
In Japan, container gardening was frequently seen in the immediate surroundings of buildings
preferably close to or even on private property and only slightly extending beyond this
‘territory’ (Jonas 2007; Shinozuka 2002; Takahashi and Shimomura 2005). When possible,
the gardens are adjacent to the building, with the exception of large arrangements which
usually spread onto the street or sidewalk. Takahashi and Shimomura (2005) showed that
many put containers on hard surfaces directly (69.3 %) but use of hangers (12.3 %) and
stands (10.5 %) was also observed. Oh et al. (2018) showed that corridor designs with a
larger area and simpler geometry significantly increase the abundance of pots in Singapore.

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Similar findings were demonstrated in a study of container gardening in Tokyo (Shinozuka,
2002). Yamamoto (2017) showed that containers tend to be placed in different configurations
depending on the width of the alley in Nagono area, Nagoya city in Japan. People tended to
put the containers either inside or outside of their property when alleys were less than 4 m
width. In alleys between 4 m and 10 m width, people put containers both inside and outside
of their private property. Over 10 m width of alleys, there was a tendency that containers
were mainly placed outside of their private property.
Street-level greenery has long played a critical role in the visual quality of the urban
landscape. Visible green ratio can be defined as the amount of greenery in the field of vision
(Ding et al., 2016). Mizukami (2013) studied 126 alleys in Kyoto, Japan and found 3.6
containers per linear meter. Although each container was small, they contributed to an
increase in visible green ratio: the visible green ratio increased linearly with the number of
containers (Y = 0.2818X + 1.7082 (R2 = 0.479)). According to this formula, a single
container could contribute to increase the visible green ratio by approximately 2%. Shinozuka
et al., (2002) studied 40 alleys (width 1.7 m – 6.9 m) in downtown Sumida-ku, Tokyo, Japan
and analyzed the relationship between width of the alley and the proportion of different
vegetation types (container plants vs. trees). They showed that the number of containers
increased as the width of the alley increased. Alleys less than 2 m wide had greater than 80%
of the vegetation provided by containers.
Communication/Social Interaction
The main requirements for maintenance of container gardens are watering, transplanting,
applying fertilizer and moving containers. An interview study showed that container
gardening was maintained by private citizens without professional help and maintenance was
a part of daily life for many people (Yamamoto 2017). In another study, most people (20 out
of 24 households), spend less than 15 minutes for daily maintenance of plant containers
(Narukawa et al., 2003). Over 90% of container garden maintenance was conducted by
housewives in a survey in Tokyo (Noguchi et al., 1999). Mason et al. (2008) studied the
consumer preference of container plants and showed that the level of maintenance
information provided were the most important attributes in the decision to purchase a
container garden.
Container gardening can contribute to enhanced communication among residents in the
neighborhood. People have been exchanging growing plants for a long time because potted
plants and their parts are suitable gifts due to their longevity and evocation of social
memories (Ellen and Komaromi 2013). People tend to propagate plants themselves and
exchange plants with neighbors. The number of containers tends to increase over time
because of this exchange. People also enjoy exchanging information on horticulture.
Container gardening is also appropriate for guided programs such as education and
horticultural therapy. Container gardens are frequently used for environmental education
because they are appropriate for observation; to get to know plants better by seeing them
close-up, by looking at them from different angles, studying their structure, texture, colour

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and seasonal change (Brandt 1977). It is relatively easy to manipulate growth conditions for
container plants, for example, it is possible to change the amount of fertilizer applied to
plants and observe their growth. Container gardens are used as horticultural therapy because
of the intimate quality and personal ownership they evoke in the garden. Container gardens
often provide a high degree of accessibility because containers can easily be raised, lowered,
or sized to meet specific access needs (Simson and Straus 1997).
Material Reuse
Plastic, terracotta and pottery are frequently used for containers. Takahashi and Shimomura
(2005) studied 115 container gardens including a total of 665 containers in front of houses in
Kyoto, Japan and showed that plastic is the most frequently used (52.8 %), followed by
terracotta (26.3 %) and pottery (6.1 %). Plastic has been used for a long time as container
materials because it is cheap and lightweight, facilitating handling. Recycled materials are
frequently used for container gardening. Many daily materials can be recycled for use in
container gardening. For example, tires, jute bags, used tins, PET bottles and even cars have
been used for plant containers (De Zeeuw et al., 2017), and the idea is virtually unlimited.
Gopal and Nagendra (2014) also showed that the types of pots used in container gardens in
Bangalore slums included earthen pots, plastic pots, cemented structures, plastic bags,
discarded paint containers, earthen water pots, plastic buckets, metallic cans, hindalium pots
(an alloy of aluminum), battery cans and aluminum buckets. Although there are many
suggestions for container materials on websites and in books, there is little quantitative
research about the materials used in container gardens. Matsuo (1977) studied 4,200
buildings in Kagoshima city, Kyushu in Japan and found that 30 % of buildings use recycled
materials for container gardening. The most commonly used were wooden boxes (31.6 %),
followed by sinks and/or washbasins (21.3 %), and polyethylene buckets (16.8 %). The
wooden boxes were originally used to transport fishes or apples. They have good aeration and
filtration and are appropriate for growing plants. The author pointed out that many kitchen
items have been converted into containers for plants. This study was carried out more than 40
years ago and current-day materials may be different, but this study demonstrates shows that
recycled materials have been used as containers for a long time.
In Japan, water left over from washing rice is commonly used for irrigation in container
gardens. Ohta and Iijima (1994) studied the awareness of water-related environmental issues
in residents in Tokyo and they showed that many people have a custom to use rice water for
plants to save resources and be more environmentally friendly. Eggshells and sea shells are
commonly put on the soil of containers or mixed with soil. It is believed that they would
release nutrients for the plants, although there is little research to show how the application of
eggshells or sea shells improves plant growth. Other studies indicate that recycled products
such as sugarcane residue and compost are commonly included in container gardens
(Vazhacharickal 2014). The use of recycled materials can make a positive contribution to the
overall sustainability of urban environments where container gardens are prevalent.

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CASE STUDIES
Container gardening is common internationally and various drivers of deployment of
container gardening have been identified. There appear to be regional differences in the
drivers and motivations for people to engage in container gardening. However, we were not
able to find papers documenting the role of culture in shaping regional practices of container
gardening. Here, we discuss further the culture of container gardening in different countries.
Roji Engei (Horticulture in Alleyways) -Japan
Domestic container gardens are commonly seen in traditional downtowns in high density
areas of Japan. This tradition of container gardening is called Roji engei (horticulture in
alleyways) (Figure 1e). While urban alleyways have long been associated with blight and
crime in some countries (Seymour et al., 2010), alleyways in Japan have a reputation as
peaceful places. These gardens consist of countless flowerpots and boxes, some are carefully
arranged and others are more chaotic (Jonas, 2007). Buildings take up most of the space in
such areas; each house is built to maximize the space occupied and container gardening plays
a role as a buffer between buildings and roads. The value of Roji engei as a community
landscape has been recognized and some studies of Roji engei have been carried out since
1990s in Japan. Roji engei as practiced in Japan, aside from reasons derived from culture,
tradition or the present cityscape, the main reason for keeping a flowerpot garden is simply
personal fulfillment in caring for plants, working with one’s own hands and creating living,
thriving, blossoming compositions of plants to enjoy, show and share (Yamamoto, 2017).
Roji engei is important as a kind of community landscape and exemplifies the value of
informal container gardening (Jonas 2007; Aoki et al., 1994). Container gardens can facilitate
conversations between residents and passers-by. Sometimes, there is no direct
communication, but people start container gardens due to the influence of their neighbor’s
containers (Manabe 1998; Yamamoto 2017).
Food Production -Africa, South America and Asia
In Africa, South America, and Asia, especially in warmer climates, domestic, informal
container gardening is a ubiquitous feature of high density urban areas. Food production is a
major goal of these container gardens (Barau 2015; Buchmann 2009; Gopal and Nagendra
2014), but across continents, these gardens also usually include a high proportion of
medicinal and ornamental plants, as well as species with spiritual importance
(Nemudzudzanyi et al., 2010) and they often feature high plant species diversity. Terrace
gardens are promoted by various government agencies in India to promote food security
among the urban poor (Nasr et al., 2017). In central America, container gardening is common
on patios, especially where paved corridors are common (González-García and Sal 2008).
Given that initiatives to promote food security in these regions aim at accessibility, low cost
systems, including creative re-use of locally availability materials, composted growing media
and water recovery for irrigation are key features of container gardens throughout the Global
South (De Zeeuw et al., 2017).

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Decoration - Europe
In Europe, container gardening tends to be used for decoration purposes. For example,
window boxes, outdoor window boxes placed under the window, are commonly seen in
Europe (Figure. 1g). Some window boxes are arranged using various kinds of flowers and
forbs, and some window boxes use a single flowering species, such as Geranium (Hiller,
1991). Hanging baskets are also commonly seen in Europe and they can support small groups
of plants in positions that would be otherwise impossible to consider: hanging on the side of a
house or on garden walls, below the branches of a tree, or suspended from the beams of a
porch, pergola, arch, or arbor (Hiller 1991).
Lack of Space, Food Production - North America
In North America, urban container gardening is often promoted as a solution to lack of space
at ground level for gardens (Bailey 1993, Choonsingh et al., 2010) (Figure 1h). The emphasis
is generally on food production. Another factor is the widespread perception that urban soils
contain contaminants, so it is believed that using soil-less media may result in less
contaminated vegetable production. Some government initiatives target not just food security
but promote container gardening in high density areas with high-rise apartment buildings as a
way to increase social interaction (Choonsingh et al., 2010).
DISCUSSION
From the above review, it is clear that published research on container gardening in urban
areas is limited. Further research on container gardening is necessary, therefore, we
recommend the following research directions to develop container gardening as green
infrastructure. Summary of this review is shown in Figure 1.
Ecosystem Service Provisioning beyond the Immediate User Community
Container gardening can contribute to various kinds of social ecosystem services in urban
areas. Many ecosystem services provided by container gardens overlap with the ecosystem
services which other kinds of green infrastructure may provide, although there are some
limitations because of the small size of containers relative to other types of ecosystems. For
example, for biodiversity, given the small relative area of container gardens, it is likely that
they may provide habitat primarily for generalist species (Cameron et al., 2012; Williams et
al., 2014). However, this may depend on the availability of other green spaces within the city;
container gardens are likely important for biodiversity in urban core areas since other green
space, such as parks, may be largely absent. Diverse plant assemblages are common in
domestic container gardens due to gardener preferences for species that perform a range of
different functions (Gopal and Nagendra 2014; Oh et al., 2018; Shinozuka et al., 2002), and
some rare native species have been observed in container gardens in Singapore (Oh et al.,
2018). Michishita et al. (2005) studied home gardens including container gardens and pointed
out that they may function as ex situ conservation opportunities because red-listed plant
species were observed. Therefore, scientific understanding of the growth conditions facing
container plants in different regions are essential to explore the potential for plant
conservation.

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In this review, one highlighted point is that much container gardening represents a
community-driven activity. Previous research on container gardening is mainly focused on
the current status of container gardening and cultural services, such as communication among
local residents. There has been little review of research on ecosystem services derived from
container gardening and many people engage in container gardening without noticing their
ecosystem services. It is necessary to study ecosystem services separately for container
gardening because its uniqueness has not been recognized. The size and diversity of
containers and plants is expected to influence the overall provisioning of benefits in urban
areas, as will the location of container gardens relative to other features of the urban
environment. Further studies are required to quantify the large-scale benefits of container
gardens. In addition, studies to show the integrated benefits of ecosystem services are
required, including a quantitative account of costs and disservices.
Ecosystem Disservices Associated with Container Gardening.
There are few references to ecosystem disservices associated with container gardening. One
important negative impact is nutrient runoff. Compared to in-ground gardening, nutrient
leaching from containers deployed on hard surfaces tends to enter urban waterways or
stormwater infrastructure where it can contribute to downstream eutrophication or at least
impose a cost for its treatment (Majsztrik et al., 2011). Additionally, the soil-less growing
media often used in container plantings can be low in cation exchange capacity, meaning less
ability to retain nutrients (Majsztrik et al., 2011). Other issues with container gardening
include greater levels of irrigation compared with in-ground gardens and green roofs, leading
to overall lower sustainability of container-based systems (Lazzerini et al., 2018). Finally,
given the popularity of ornamental plants in container gardens worldwide, and the propensity
for ornamental species to become invasive in natural ecosystems (Kowarik 2005), container
gardens, like other kinds of urban horticulture can increase the risk of invasive plant species
introduction.
Plant Selection, Growth Environment and Materials for Container Gardening
Previous plant studies were carried out through observations on plant choices in container
gardening and indicated that plant selection for container gardens incorporates high species
diversity. Container gardens can contain a high number of plant species within a small area.
Private or home container gardens show a range of forms and diversities, from messy to
decorative. Conversely, plant selection for container gardens that are installed by companies
or governments may be decided by practical reasons of plant availability or ease of
maintenance, and tend to show less individual variation due to conventions of public
landscaping.
Very little research has been carried out to investigate the unique growth environment faced
by plants in container gardens. Maximizing the benefits of container gardening as green
infrastructure will require knowledge of growth conditions to aid in the selection of
appropriate plants and improve maintenance. Further experimental studies are required in
controlled environments to choose appropriate plants for container gardening in urban

J. of Living Arch 8(2) Feature 13
environments. These could include screening for drought tolerance, water and temperature
requirements in small containers for regional climates.
It is important to recognize the differences between in-ground urban gardens and container
gardens in terms of the environment for plant growth. From an ecological perspective, the
main difference between in-ground urban gardens and container gardens is the isolation of
the substrate and plant roots from soil in the ground and from the roots of other plants. Green
roofs and walls may incorporate containers as well, but container gardening on the whole
tends to employ smaller containers. This can be an advantage to gardeners as the smaller
containers are easily moved, but the containers present several challenges to plant survival
and growth. Container plants can experience more extreme temperatures than plants growing
in the ground (Young and Bachman 1996), therefore, root damage is possible, resulting in
reduced capacity for nutrient uptake (Mathers 2003). Root restrictions due to confinement in
pots is commonly reported in horticultural research (Di Benedetto et al., 2006), leading to
reduced growth rates and water uptake. Container size relative to the plant species grown is
an obvious consideration for maximizing plant survival and growth (NeSmith and Duval
1998). Since the growth environment for container gardening can be severe, it is important to
choose appropriate container size and materials. Innovations in container design featuring
alternatives to traditional smooth-sided containers can reduce circular growth around the pot
and root death (Amoroso et al., 2010). Caputo et al. (2017) point out that containers placed on
hard surfaces can have drainage issues, e.g. waterlogging of roots, that would not usually
occur with in-ground plantings, unless there is some space between the roots and containers,
so container design and placement is important.
The growth environment may affect plant selection for container gardening. For example,
studies in Mediterranean climate cities indicated that the harsher conditions in containers
resulted in gardeners choosing more non-native succulents in high density urban habitats
compared to lower density areas where containers were less common (Marco et al., 2008).
Maximizing the benefits of container gardening as green infrastructure will require
knowledge of growth conditions to aid in the selection of appropriate plants and improve
maintenance. Further experimental studies are required in controlled environments to choose
appropriate plants for container gardening in urban environments. These could include
screening for drought tolerance, water and temperature requirements in small containers for
regional climates.
From our review, it is apparent that recycled materials were frequently used for container
gardening. Recently, research on the life cycle assessment (LCA) of urban greening materials
has increased. LCA examines the environmental impact associated with products or systems
throughout their life cycles. Considering the whole life cycle of a system, the environmental
burden due to the extraction, transportation, production, and construction of raw materials is
largely dependent on the type of system and materials involved (Perini and Roccotiello
2018). Recycled materials may be used as for pragmatic reasons, such as their availability to
gardeners, but there may also be an awareness of broader environmental concerns driving
these practices.

J. of Living Arch 8(2) Feature 14
Policies to Support Formal and Informal Container Gardening
Previous studies demonstrated that container gardening provides several benefits such as
community development and improvement of visual quality in urban landscapes. In many
cities, funding for urban landscaping has decreased, therefore, urban greening by citizens is
getting more and more important (Mattijssen et al., 2017). However, currently, city planning
and politics have paid little attention the fact that informal gardens shape cities to a large
extent. From our review, it was shown that container gardens were often established by
private citizens without professional help and maintenance was a part of daily life for many
people. Container gardening, even as a voluntary and leisure activity has significant social
and ecological implications that cannot be simply ignored. Mattijssen et al. (2017) studied the
long-term management or ‘place-keeping’ of urban green space by citizens and found that
the supporting role of authorities was key in legitimizing and supporting place-keeping by
citizens. Authorities can support place-keeping by citizens by providing security via stable
policies, formally protecting the involved spaces, allowing long-term management contracts
and contributing resources. Place-keeping can be defined as ‘responsive long-term
management which ensures that the social, environmental and economic quality and benefits
a place brings can be enjoyed by present and future generations’ (Dempsey and Burton
2012).
Although container gardening is popular in Japan, only a few local regulations deal with
container gardening directly and no laws apply to them (Jonas 2007). Some local authorities
provide funding and materials such as plants and flower pots for container gardens, but most
of them target group activities in public areas (e.g. Nagoya city in Japan). In Hong Kong,
government initiatives promote container gardening in high density areas with high-rise
apartment buildings as a way to increase social interaction (Choonsingh et al., 2010).
Similarly, some government initiatives are promoting container-based food production in
cities, for example, in Bangalore where over 14,000 people have a terrace container garden.
These gardens use a variety of purchased and recycled containers to grow over 50 species of
fruits and vegetables (De Zeeuw et al., 2017). It would be valuable for local governments to
play a greater role in encouraging container gardening. By using container gardening,
households can voluntarily extend urban greening projects into other public spaces within
their neighborhoods in a way and manner that local planning authorities could not ordinarily
achieve (Barau 2015). It may be important to keep their activities bottom-up (informal) rather
than top-down (formal) because much container gardening is spontaneous and results from
the expression of individual tastes and preferences.
We were not able to find any papers to describe formal container gardening. Some city
councils have policies to encourage formal container gardening. For example, city councils
offer sponsorship, such as Aberdeen in the UK, offers sponsorship opportunities for floral
displays (e.g. containers and hanging baskets) across the district. The sponsors purchase
hanging baskets and containers from Aberdeen City Council, who will install and maintain
them throughout the season (Aberdeen City Council 2020). These kinds of activities may
encourage container gardening and future academic research of formal container gardening is
required.

J. of Living Arch 8(2) Feature 15
From this review, it was shown that container gardening can contribute to increase the visible
green ratio and the distribution of container gardening was influenced by the design of space.
Therefore, space design and city planning that facilitate container gardening are required. For
example, window boxes are deeply rooted culture, and they can represent a symbol for
particular cities. Currently, it seems that there are no regulations nor obligations to have
flowers. The activities of container gardening should be optimized to realize increased
greenery in cities.
CONCLUSIONS
This study showed that container gardening has a potential to be an important component of
urban green infrastructure. It is clear that container gardening can contribute to various kinds
of ecosystem services in urban areas. In this study, only English and Japanese language
papers were studied and there may be some literature in other languages on container
gardening. Further studies are necessary to understand what the drivers of container
gardening in different countries are.
Developing container gardening as green infrastructure or living architecture is challenging
because very limited information is available to show the current extent, value and effects of
container gardening in urban areas. To develop container gardening, it is important to engage
citizens, local authorities and academia. It is important for citizens to be aware that they can
contribute to improving the urban environment although much container gardening may be
done as a hobby. Local authorities should be aware of the potential to support their activities
through policy and inform the value of container gardening in town planning. In academia,
further research on container gardening should be undertaken to show its value and effects on
the urban landscape. Cooperation among academics, local authorities and citizens is required
to further develop container gardening to provide many direct and indirect benefits to people
living in cities.
ACKNOWLEDGEMENTS
Funding for this project was provided by Chiba University SEEDS Fund (Chiba University
Open Recruitment for International Exchange Program). We would like to express our
gratitude for the useful advice from Dr. Nick Williams at the University of Melbourne and
Dr. Scott MacIvor at the University of Toronto, and to Mr. Atsushi Saito, Saito advertising
inc. for the improvement of figures.
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