Gardens are places that have continuously been part of the human residential environment, and are perceived as spaces in which human activities are carried out, from private spaces to public open spaces like parks (Woo and Suh, 2016). Gardens created as a green space within the sphere of human living are tended to and cultivated by citizens in their daily lives in various parts of the city. These can be created as a space with an unconstrained form, familiar shape and practicality through the leisure activities of citizens (Sim and Zoh, 2015). Urban gardens involve planting various kinds of plants in the city. They may also involve the establishment of a relevant environment in the city, comprehensively indicating that gardens form part of said city (Ernwein, 2014). Urban gardens that appear to be an efficient use of space in small land are extremely small pieces of green space that trigger interactions among local residents, building an urban image of gardens created in a complex structure (Sim and Zoh, 2015).

According to Table 2, physical environment 37.73% and social environment 62.27% were studied in garden-related articles in Korea and overseas. Through a comparison of Korean and overseas articles, it was found that in Korea more articles were focused on place elements and psychological and physical health, while overseas more articles were focused on ecological elements, public service and administration. Key findings of Korean and overseas studies on the physical and social environment of gardens and green spaces in the city are as shown in Table 3, Table 4 and Fig. 2 below.

According to Fig. 2, of the types of urban gardens studied, community gardens represented the highest portion both in Korea and overseas, with the percentage nearing 50% overseas.

Community gardens literally are “gardens in the community or neighborhood in which one lives.” These are gardens for the neighborhood, and form a community by extending the fences to the neighborhood. Emphasizing neighborhood gardens connotes the meaning of “shared gardens for the community.” Neighborhood gardens are characterized by people in the neighborhood sharing the place to enjoy, and not to possess nature on their own (Sung and Lee, 2013). Community gardens are known to not only cultivate crops and improve and protect urban spaces, but also to contribute to the formation and strengthening of the community based on cooperation among residents of all races and generations (Park et al., 2011). Because of this, the attention to community gardens is received thereby. Urban community gardens are mostly formed in the middle of the city or suburban areas, and can be categorized into neighborhood living type (located within walking sphere including private land), idle land utilization type (remnant land, vacant land, street greenery, etc.), residential complex type (detached housing or apartment district), and base connection type (parks or public facilities) (Choi et al., 2018). In 2014, average green area per capita of 29 OECD countries was 520.41 m², with Korea ranking 26^th for green space at 57.91 m² per capita (United Nations Human Settlement Programmes, Global Urban Observatory, 2018). Moreover, other countries tend to divide and use sections where enough public space can be secured, such as big open spaces or park spaces. On the other hand, Korea tends to form rectangular land modules as a simple space (Sung and Lee, 2013). In the densely integrated residential space in Korea, the gardens can be moved in narrow yards and street spaces, and flexible type (76%) gardens that occupy a minimum area are found to be more common than the fixed type (21%) (Sim and Zoh, 2015) (Table 5). The governance structure of urban community gardens can be classified into 6 types (Table 4). To use community gardens to activate social capital and promote community elasticity, a bottom-up governance structure with good connection and management will be the most effective, and will be successful as long as the community has the motives and can secure sufficient public funds and support (Fox-Kämper et al., 2018). The Sydney guidelines specifically provided facilities that can be applied according to the size and the number of people needed (up to 100 m², 15 or more; around 400 m², 25 or more; 1,000 m² or more, 40 or more) in the community gardens (City of Sydney, 2016). In the Korea guidelines, size (up to 100 m², 101–200 m², 201–400 m², 400 m² or more) and participants (under 5, 6–10, 11–20, 21–30, 30 or more) were found in the checklist, but there was no specific explanation (Rural Development Administration, National Institute of Horticultural and Herbal Science, 2020). In the Act on the creation and furtherance of arboretums and gardens, an area of 300,000 m² was proposed as a requirement for designation of a national garden (National Law Information Center, 2019a). According to agricultural laws, garden sizes were up to 400 m² in Germany, up to 300 m² in the U.K., 10–30 m² or 100–300 m² in Japan (Hwang, 2010). The size of a garden for operating an urban agricultural community was suggested to be 100 m² or more in Korea (National Law Information Center, 2019b). As such, it is necessary to present standards for creating communities through gardens in the Act on the creation and furtherance of arboretums and gardens based on overseas cases and the Act on the development and support of urban agriculture.

The second-highest portion was taken up by rooftop gardens in Korea and kitchen gardens overseas. In addition, there are differences in the types of gardens studied in the papers, such as alley gardens, therapeutic gardens, national gardens, vertical gardens in Korea, and allotment gardens in overseas (Fig. 2).

Rooftops and roofs capable of green planting in Seoul take up approximately 70% of the city, which shows the possibility of rooftop gardens. This also suggests that roofs can supplement the lack of green space, solve the city’s ecological and environmental problems, and even become cultural spaces (Lee et al., 2014). Thus, this result reflects the enthusiasm in using rooftop gardens. Vertical gardening is one of the most useful ways to expand urban green space by covering the walls of buildings or other structures with trees or flowers. Rooftop and vertical gardens can be a very effective alternative to increasing the urban greening rate if the artificial greening method is applied to buildings that are available from the overall perspective of the city, even if the area of the artificial greening by each building is not large (Park, 2012). As the rural population gathered into big cities in the 1960s, leading to a severe housing shortage, apartments were chosen as a method to increase residential density in limited land space (Lee et al., 2017). Currently, apartments represent 49.2% of all housing in Korea (Korean Statistical Information Service, 2019). Certain side effects resulted from the fact that urban neighbors were strangers to one another, unlike in rural communities where neighbors were mostly family and close relatives along with and lived together in the same area. One paper stated that a person was hit and killed by an object that fell from the upper floors down to the ground, the desolate and artificial environment surrounded by concrete causes psychological problems such as depression, and inter-floor noise complaints was frequently caused in apartments (Lee et al., 2017). Recently, amenity has been the highest priority among apartment considerations, apartment complexes with a view of nature such as parks, forests or rivers are preferred, and community spaces that had merely been providing exercising or learning facilities are now turning into places where the whole family or residents can enjoy leisure together (Park, 2019). Apartment residents desired social interaction rather than an isolated form of living that emphasizes anonymity, highlighting the necessity of shared spaces for the purpose of promoting mutual interaction (Kim et al., 2010). The trend in new apartments is taking the form of public gardens where they have a park or gardening facility 2.5 times bigger than a soccer field. They also use 40% of the complex area for landscaping, allowing the residents to tend gardens on part of the expanded space of the living room balcony. In addition to these, they also have a themed garden walkway. Moreover, places with increased residential amenity can also anticipate huge profits when selling the apartment (Jung, 2019a, 2019b; Lee, 2019).

Overseas, gardens have spread out in the UK, Europe, and North America to make up for food shortages during war, playing a key role in national food security by providing essential nutrients that could not be supplied by the environment at the time (Egli et al., 2016; Ginn, 2012). Because of this, gardens have been developed with an emphasis on food supply for low-income groups, which is why many studies overseas are on kitchen gardens. Allotment gardens also have been shown throughout history to provide long-term food security in times of energy scarcity (Barthel and Isendahl, 2013), and average allotment garden area was 1.2 ha in Manchester (UK) and 10.2 ha in Poznan (PL) (Speak et al., 2015). Social inequality in the area of food is caused by sociocultural determinants, economic constraints, and unequal access to healthy food. Thus, the dietary formula of low-income groups lacks fruits and vegetables (Martin et al., 2017). A “food desert” is an area that lacks accessibility to affordable and nutritious food, and these can be found in cities and rural areas of North America. Community gardens provide group members and other residents with fresh vegetables and fruits, contribute to making a healthy dietary pattern, and reducing health risks (Wang et al., 2014). They also help students have a healthy diet of vegetables and fruits, while changing their dietary habits and knowledge about food production. Various plants of 66 genera and 159 species were discovered at community gardens in school built for education, health, and environmental sustainability (Guitart et al., 2014). Households that include gardeners tended to use more diverse agricultural products than those that do not (Martin et al., 2017). Gardening activities in community or school gardens are affordable and practical methods to secure safe food supply and improve health for urban residents and students.

Korea has come to focus on the rooftop space due to its small land area, and the most common residential type is multi-unit buildings like apartments, with public gardens formed within the complex. In other countries, people promote health by carrying out gardening activities combined with kitchen gardens and by producing safe vegetables and fruits. It is a global trend to harmonize the residents with gardens and promote recovery of the community. As such, it is necessary to form gardens, including kitchen gardens in rooftops or apartment complexes, and run them in the form of community gardens in which all residents can participate together.

Creating a new urban park over a certain size involves many difficulties, which can include compensation for stakeholders regarding the existing building or land as well as a large budget and time investment. As such, the alternative is to build green space networks by forming small green spaces within the neighborhood such as gardens. To preserve urban biodiversity, small gardens in addition to parks can also serve as habitats as extensive and unique resources. They may also function as green corridors that form an ecological network (Goddard et al., 2010). Green spaces in a city with high biodiversity provide greater physical and psychological benefits for the public, and can even increase the resilience of the urban environment (Fuller et al., 2007). For this reason, building a green space network by forming small green spaces and securing connectivity is being considered an important initiative for creation and management of urban green spaces (Han et al., 2014).

A connectivity assessment was conducted on green space networks by classifying the green spaces of a built-up area with high density in Korea, and it was found that green spaces in the target site were distributed in the order of street greenery, private garden, remnant vacant lot, park, and roof garden. Remnant vacant lots and street greenery were the spaces with highest potential for green corridors (Choi et al., 2017), and 20% of the cases were found in public areas of streets, following private areas inaccessible from the outside such as rooftop gardens or terraces (33%) (Sim and Zoh, 2015). This reflects the traditional view of life in streets, in which some people still extend their living space out to the streets, although this has decreased since urbanization began. This implies that small gardens using remnant vacant lots and street greenery can improve accessibility to green space.

Looking at green spaces of campus in France, 1/3 were simple green spaces (32%) with just one type of component, whereas the rest had two or more components of green spaces (68%). Urban services in the campus green spaces are classified into water management, use of space, improvement of biodiversity and well-being, and all urban services related to promoting biodiversity are provided by the green infrastructure on campus, thereby showing a great potential for important biodiversity (Belmeziti et al., 2018). In general, studies in Korea have tended to categorize urban green spaces with a focus on space, whereas overseas studies have focused on the components of green space and analyzed urban services accordingly.

An allotment garden is one form of service to provide rights to use an accessible place near residence at a low cost for citizens or the community and induce cultivation of vegetables and social interaction (Kim, 2011). Allotment gardens had higher plant species richness than parks (Table 3). This may be due to the difference in the land management customs between parks and allotment gardens - since parks weed regularly, the number of species that can survive might be limited (Speak et al., 2015). Moreover, an investigation of the biodiversity of 70 gardens in Colombia led to the discovery of a total of 82 genera, 240 species, and 4,110 individuals. Furthermore, the average species richness of the gardens was 15.4, with older gardens showing higher species richness (Sierra-Guerrero and Amarillo-Suárez, 2017). In the UK, plant richness varied depending on the size of green space. This shows the measurable positive correlation between the rich species of urban green spaces and the well-being of visitors. Psychological benefits were positively correlated with plant species richness and birds, and such benefits increased in green spaces where plants’ and birds’ richness is generally high (Fuller et al., 2007). Bird diversity in urban areas tends to be proportional to the volume of existing vegetation (Savard et al., 2000).

It is difficult to secure green planting space in urban centers with high building coverage; green space networks can be built in a city by creating small green spaces within the living zone. It is effective to build gardens for small green spaces using street space, remnant vacant lots and rooftops. Moreover, more diverse plant species can inhabit gardens than parks, which promotes biodiversity and thus has a positive effect on the health of the urban ecosystem. As a consequence, small spaces such as a vacant lot, pocket of land, or a rooftop can be used to build gardens in Korea, which would be used as a base reference to promote the reasonable values of garden construction. In addition, if a feasible guideline is produced in order to utilize a small size vacant land in a productive way, it should be adopted through supportive legislation by the municipalities to apply an approval of promotion policy.

Community gardens can help residents maintain a healthy weight, promote physical activities, secure food supply, increase their ownership and pride in the region, and support urban aesthetics and community cohesion (Egli et al., 2016).

High consumption of vegetables and fruits and improve regular physical activity and directly affect health, and garden activity is a form of physical exercise that offers benefits in the areas of fitness, health and well-being (Van den Berg et al., 2010; Kingsley et al. 2007), and can help prevent obesity in adults (Zick et al., 2013). Community gardens can provide fresh vegetables and fruits for group members and other residents, and can also resolve the aforementioned issue of food deserts (Wang et al., 2014). Food prices were high during the Cold War, so garden cultivation provided an alternative food supply, and helped stabilize the economy (Shin and Choi, 2018).

A therapeutic garden means a garden that draws energy to the body and vitality to the mind, ultimately bringing out the rhythm to restore the weak body and mind to its original state (Park and Lee, 2014). People who participated more in community gardens, lived closer to community gardens, and can see community gardens from their residences tended to show greater psychological and social benefits (Kim and Lee, 2013). The total mean of the three psychological indicators was the highest in forests, followed by rooftop gardens and cities. Considering that rooftop gardens have greater accessibility than forests, they may be more excellent than forests in terms of their positive effects on mental and physical health of urban residents in everyday life (Lee, 2011). Moreover, proximity to the natural environment induces interest in components of green spaces, even in the urban environment, and helps establish the foundation for knowledge building (Sampaio et al., 2018).

Nordh and Ostby (2013) showed that small urban parks must be designed with natural components protected from the disturbance of surroundings, promote opportunities for restoration experience, and have certain seats to function as a venue for social encounters. To improve the alley environment, it was found that there was a need for a space for interaction and rest, and the satisfaction with the alley garden was also high (Jang et al., 2017).

Furthermore, community gardens are more similar to biointensive high-production farming than conventional agricultural practice (Algert et al., 2014), and thus may bring economic benefits through cost reductions. In Korea, when willingness to pay (maximum amount a buyer is willing to pay to own rather than to live without any product or service) was compared, classifying urban green spaces into mountains, forests, rivers, streams, lakes and urban neighborhood parks, it was found that when there was a green space within a 10-minute walk from the residence, housing had an 18% higher value on average for apartments, and a 20% higher value for detached houses (Choi and Eom, 2018).

The result of PRS measurement was highest for forests, followed by rooftop gardens and cities. Items that contributed greatly to capability of being restored were natural elements such as grass, flowers, plants, and water. As such, citizens close to gardens showed high psychological well-being and life satisfaction as well as low stress, increased interaction with neighbors, and greater crime prevention effects. Gardens also have positive effects on urban aesthetics such as safety of alleys, cleanliness, and greening, as well as the issue of food deserts, producing significant psychological and social effects. Gardens have great accessibility to urban residents and provide as many psychological benefits as forests, and thus are efficient means to promote mental and physical health. Contact with green spaces such as gardens in the city is also an effective way for students to obtain knowledge about environmental components and biodiversity.