Greenness Index and Preferences for Interior Landscapes in Residential Spaces

Abstract

Modern people have limited opportunities to experience the natural environment due to reduced outdoor activity time and are not provided with enough opportunities to encounter landscape, even in indoor spaces. Due to the current COVID-19 pandemic, the time spent indoors is getting longer. As the number of health-conscious people increases, interest in the introduction of indoor plants, which help purify the air and improve emotional stability, has increased. This study aimed to identify the direction of creating interior landscapes in residential spaces by examining the Greenness Index (GI) and resident preferences. This study targeted 65 households in residential spaces with over two rooms and growing plants. Pictures and descriptions of interior spaces were collected and analyzed. Case studies were conducted to analyze interior landscape planning preferences. The results indicated that public spaces (72.3%) contained foliage plants (98.5%) and containers using soil (93.8%). Residents perceived all components, from plants to containers, considering the GI. Residents’ subjective perceived GI (15% on average) was higher than the objective GI (10% on average) calculated from photos. Psychological stability and visual beauty were high for all items. Preferred locations for interior landscapes were living rooms (55.4%), which are public spaces, and living room verandas (38.5%), which are functional spaces, with foliage plants (52.3%) being predominant. These findings indicated that interior landscape could link the indoor environment in residential spaces and external spaces using nature, creating aesthetic and environmental effects indoors. Furthermore, this study is meaningful, as it identified residents’ preferences for interior landscape planning in residential spaces.

1. Introduction

Research Purpose

As modern people spend more time indoors, they have limited opportunities to encounter the natural environment and insufficient opportunities for natural landscaping in indoor spaces [1,2]. In addition, there are continuous indoor environmental pollution issues, such as sick building syndrome [3]. To solve these issues, efforts have been made to introduce plants indoors and focus on improving environment quality by securing green spaces indoors [4,5,6,7,8]. Currently, as more people are concerned with their health due to the COVID-19 pandemic, interest in introducing indoor plants that help purify the air and bring emotional stability has increased [9,10,11]. In Korea, several new terms were developed, including planterier, a compound word of plant and interior; home gardening, indicating bringing the garden into the home; and pet plant, which uses the term pet, meaning a companion to spend one’s life with [12].

Nature is a fundamental element that gives people mental stability and relaxation. Introducing plants into residential space creates a higher quality residential environment and improves the emotional stability of residents due to aesthetic and indoor environmental effects and connection between interior and exterior environments through nature.

The Greenness Index (GI) refers to the amount of green space compared to the entire landscape. The GI has a close relationship with psychological stability and comfort [13,14,15,16]. Seoul has been inducing a higher quality of life by providing green spaces to citizens, setting the average horizontal GI target value of 30% in the Seoul Environmental Vision 2020 and the 2020 City Master Plan [17]. In Japan, the index for street planting has been used in the Basic Plan for Green Spaces, and items to measure and evaluate the GI were introduced in the first green promotion plan in Kyoto in May 2011 [15].

Therefore, the GI has been used to create green environments outdoors. However, research on the GI in indoor spaces, such as target values, standards, and preferences, is lacking. Previous studies indicate that GI comfort effects and preference levels differ based on spatial usage [14,15,16,17,18,19,20,21,22,23].

Therefore, this study investigated the GI of interior landscape spaces in residential spaces and residents’ preferences.

This study is in the first stage in the composition of the interior landscape model in line with the GI in residential spaces. This study lays the foundation for proposing the direction of environmental improvements using interior landscape planning.

2. Indoor GI in Residential Spaces

2.1. Housing Types and Spatial Composition of Residential Spaces

Houses can be broadly classified into detached (including detached houses, houses in multiple occupation, multi-unit houses, and spaces) and multi-unit dwellings (including apartments, row houses, multi-household houses, and dormitories) (

Table 1. Spatial Composition of Residential Spaces.

Residential Space	Classification
Public spaces	living room, dining room, kitchen, multi-room
Private spaces	couple’s bedroom, children’s room, parents’ room, bathrooms
Functional spaces	utility room, storage, veranda,

) [24]. In Korea, approximately 78% of residents live in multi-unit dwellings, with approximately 64% of residents living in apartments [25].

Residential space contains public spaces shared and used by family members, such as the living room, dining room, kitchen, and multi-room, private spaces requiring privacy in which individual activities are performed, such as couple’s bedroom and children’s room, parents’ room and bathrooms, and functional spaces that enhance work efficiency by linking with other spaces or storing daily necessities [26].

Accordingly, this study classified the types of houses into detached and multi-unit dwellings and residential spaces into public, private, and functional spaces. Housing types and spatial compositions were considered in the interior landscape analysis.

2.2. Classification of Interior Landscape Techniques

Interior landscape techniques can be broadly classified into three styles: garden, planter, and container style based on plantings [27]. In addition, seven detailed styles can be distinguished: garden, planter style, tree planting, hanging, hydro-culture, container, and large container styles (

Table 2. Classification of interior landscape technique.

Technique	Style
Planting technique	garden style
	planter style	planter style
		tree planting type
		hanging type
		hydro-culture type
	container style	container style
		large container type
Form technique	island style
	cascade style
	3d style
Structure technique	entrance style
	count style
	mall style

).

The garden style is a method of dividing the range of the interior landscape using boundary markers or natural stones and installing soil and drainage facilities. The planter style is an architectural type in which the planter is architecturally prepared in advance when an atrium is installed. The tree planting style uses a foundation supporting the tree installed under the ground. The hanging style is a technique of greening around a vertical part, such as walls or pillars. The hydro-culture style utilizes hydroponics with hydro balls instead of soil.

The container style is a technique of planting and arranging foliage plants in decorative pots, and the large container style is a method of planting trees in large pots, which is often seen in atriums.

This study classified and analyzed interior landscape types in residential spaces based on planting techniques.

2.3. Classification of Plants in Interior Landscapes

According to the Korean Horticultural Therapy and Wellbeing Association [28], landscape plants can be classified into three types based on plant growth, use purpose, and valued plant portion (

Table 3. Classification of interior landscape plants.

Classification	Categories
Plant growth	tree
	shrub
	a vine plant
	ground cover plant
Use purpose	greening
	hedge and shielding
	windproof
	dustproof, sand proof, smokeproof
	reclaimed Tidal Land
	fire prevention
Appreciation part	flowers
	fruit
	leaves
	maple leaves
	color or pattern of stems

).

Plants in interior landscapes can be further divided into five categories based on the valued portion: flowers, fruits, leaves, autumnal tints, and color or pattern of stems.

This study aimed to investigate the GI in residential spaces with interior landscapes and analyze the comfort level of the GI. Therefore, this study classified interior landscape plants based on the appreciation part.

2.4. Existing Studies on Indoor GI

Ishii and Sagawa [21] investigated the psychological comfort and preference of college students and the elderly using 54 indoor and outdoor landscape photos and found that higher GI was associated with higher comfort in all age groups and preference levels were high for indoor GI of 20–30% and outdoor GI of 50% or higher.

Yoo [16] created an interior landscape model and evaluated its spatial application for workplaces. The results indicated that users generally preferred a GI of 10–20%, the container style, and plantings with a mixture of 2–3 plant types with abundant leaves horizontally and vertically. In addition, attention restoration was high at a GI of 20%. High recovery environments were observed when plants were arranged on the ground in a symmetric way or on the wall in a connected pattern rather than a separated pattern.

Kubota et al. [29] introduced plants in an office space by changing the plant types once every two weeks, a total of nine times and measured the psychophysiological responses of workers. The GI level ranged from 0% to 10%. Foliage plants, mint, basil, and begonia were effective in reducing physiological stress and psychological fatigue.

On the other hand, Hashimoto et al. [23] took photos of a laboratory in a university, edited them with Photoshop, and investigated the GI preference in the workspace via interviews. The respondents preferred a model with a GI of 3.2% over 2.8% or 3.8% and did not prefer green interiors such as partitions and chairs.

An [18] created a model based on the GI for a coffee shop, which is a commercial space; they conducted a survey, which revealed that the respondents preferred distributed plants and a model with a GI of 5%.

Choi [22] conducted physiological experiments using heart rate variability and brain waves and surveys after arranging Devil’s ivy (Epipremnum aureum) on the wall based on the GI levels (i.e., 5%, 20%, 50%, and 80%) in a laboratory. There were no differences in heart rate variability and brain waves based on GI levels, indicating that a GI of 5% was sufficiently effective.

Extant studies on interior landscapes mainly focused on workspaces due to the correlation between work efficiency and landscape plants and on the utilization of interior landscapes to improve marketing effects and spatial image in commercial spaces. Previous studies included field research, evaluation of preferences for photo images, physiological response experiments, and laboratory observations.

However, studies on interior landscape design and the GI in residential spaces remain insufficient. Further research on residential spaces is required, as the preferred GI level differs depending on the target spaces.

In addition, while many GI-related studies target outdoor green spaces, studies on indoor GI are scarce. GI-related studies, for example, to target outdoor green spaces, Lee and Shin-ha [30] implemented a greenery module to enhance GI of an alleyway and analyzed the landscape preference and landscape characteristics (SD scale) for alleyway users. As a result, as the GI increased, the preference level for the scenery was higher. In the case of landscape characteristics, characteristics such as ‘natural’, ‘warm’, and ‘harmonious’ were found to have increased. Song et al. [31] proposed a dynamic method to assess urban greenspace exposure by integrating mobile-phone locating-request (MPL) data and high-spatial-resolution remote sensing images. Song, Chen, and Kwan [32] integrated multi-source geospatial big data and nighttime light satellite images to quantitatively estimate changes in people’s exposure to green environments for 290 cities in China from 1992 to 2015. Hsu et al. [33] investigated the population density and distribution and pattern of green areas in four large cities in Australia by using the GIS approach and analyzed green accessibility.

Additional objective data are required, and it is necessary to examine whether indoor and outdoor GI could be calculated in the same manner and are perceived similarly.

Therefore, this study investigated interior landscapes and GI characteristics in residential spaces.

3. Materials and Methods

3.1. Research Scope and Method

This study conducted a literature review and empirical research to identify the current status and preference characteristics of interior landscapes in residential areas.

First, we reviewed previous studies related to interior landscape planning and the GI in residential spaces, such as house types, spatial composition of residential spaces, classification of interior landscape techniques, classification of interior landscape plants, and indoor GI. Through this, the GI components in residential spaces were identified.

Second, we targeted 70 households who live in residential spaces with more than two rooms in Korea and grow plants. At the time of the research, field observations were not possible due to the outbreak of COVID-19. Instead, under the researcher’s guidance, the research targets directly observed and took photos of their interior landscape spaces and sent the contents to the researcher. The photos and observations were analyzed to identify the interior landscape features in the residential spaces (Figure 1).

Third, an online survey was conducted on preferences for interior landscape planning within residential spaces with 70 participants, which included one member from each household subject to case studies.

3.2. Research Target and Details

To understand interior landscapes based on house types and composition of residential spaces, this study targeted residential spaces with interior landscapes and more than two rooms in Korea and surveyed dwellers in these spaces.

The survey analyzed general and housing characteristics of the participants, characteristics of the interior landscape arrangement, and GI environment characteristics. General and housing characteristics encompassed gender, age group, housing type (detached or multi-unit dwelling), location of the house’s direction (east, west, south, etc.), and housing area. Interior landscape arrangement characteristics included location (public, private, or functional spaces) and style (container, planter, garden, or mixed). GI environment characteristics included perception of GI ranges and objective and subjective GIs (%). There are two methods to calculate GI: focusing on attributes including all leaves, flowers, branches, and stems of trees and focusing on chromaticity, that is, leaf color [13]. This study utilized the former method, as it is based on the GI area.

3.3. Research Method

The study was conducted from 18 June to 17 August 2020. The study included 70 individuals from their 20 s to 50 s.

35 subjects per group were calculated by referring to previous studies [16,34,35] related to the survey on the status of interior landscapes. The target spaces were divided into public spaces and other spaces (private spaces, functional spaces), and a total sample of 70 people was selected.

Photos were taken based on the GI measurement method [16,22,36]. As for the measurement method, first, position was established in a location where the space for growing plants can be seen at a glance and second, photos were taken by adjusting the downward angle within 20° from the line of sight at a height of 1.5 m such that the plants placed at the bottom could be seen. If the target spaces could not be clearly seen due to the space structure, the participants were asked to shoot the spaces twice from different angles.

The online survey targeted the same group of 70 individuals. The questionnaire consisted of housing type, housing area, housing direction, locations of the landscape arrangement, perceived GI (subjective GI), and perceived GI ranges.

A total of 65 photos (65 individuals) were used, excluding five unclear photos (except for cases where the angle of the photo is not correct or only the plants, not the interior landscape space, are taken by zooming in), and the GI was analyzed using Adobe Photoshop CS6. When two or more photos were taken in the same residential space (1 individual), each GI was calculated, and the average value was used. In addition, if photos from a residence were not used, the survey answers from the participant from that residence were not used. The frequency analysis and the Mann–Whitney U test were performed using the statistical analysis program SPSS Statistics 25.

4. Analysis of Interior Landscape Spaces and GI Characteristics in Residential Spaces

4.1. Participants’ General and Housing Characteristics

The general characteristics of the respondents are presented in

Table 4. Demographic Characteristics N (%).

Demographic Characteristics		N (%)
Gender	male	9 (13.8)
	female	56 (86.2)
	total	65 (100.0)
Age	20s	10 (15.4)
	30s	16 (24.6)
	40s	17 (26.2)
	50s	22 (33.8)
	total	65 (100.0)
Housing types	multi-unit dwellings	57 (87.7)
	detached houses	8 (12.3)
	total	65 (100.0)
Housing direction	east	7 (10.8)
	southeast	9 (13.8)
	south	38 (58.5)
	southwest	7 (10.8)
	west	4 (6.2)
	total	65 (100.0)
Housing area	multi-unit dwellings	average 114.45 m2
	detached houses	average 102.48 m2
	total	65 (100.0)

. The participants included 86.2% (n = 56) women and 13.8% (n = 9) men. Of the participants, 33.8% (n = 22) were in their 50s, 26.2% (n = 17) were in their 40s, 24.6% (n = 16) were in their 30s, and 15.4% (n = 10) were in their 20s.

Multi-unit dwellings accounted for 87.7% (n = 57) and detached houses for 12.3% (n = 8). Of the houses, 58.5% (n = 38) were located in the south, 13.8% (n = 9) in the southeast, 10.8% (n = 7) in the east, 10.8% (n = 7) in the southwest, and 6.2% (n = 4) in the west. Multi-unit dwellings were 114.45 m² on average, whereas detached houses were 102.48 m² on average.

4.2. Characteristic of the Interior Landscape Arrangement in Residential Spaces

Locations of interior landscape arrangements in line with the spatial composition of the residential spaces are presented in Table 1. Public spaces accounted for 72.3% (n = 47), whereas functional spaces accounted for 27.7% (n = 18). Most of the interior landscape was installed in public spaces, such as living rooms. The container style accounted for 93.8% (n = 61), whereas the mixed style, including a complex combination of container and hanging planter styles, accounted for 6.2% (n = 4). Most of the interior landscapes were arranged in a container style, which is easy to maintain and move (

Table 5. Classification of interior landscape in residential spaces N (%).

Classification		Total
Spatial Composition	public spaces	47 (72.3)
	functional spaces	18 (27.7)
	total	65 (100.0)
Planting technique	container style	61 (93.8)
	complex style	4 (6.2)
	total	65 (100.0)

and Figure 2).

As for plant types based on appreciation parts, plants valued for leaves accounted for 98.5% (n = 64), plants for leaves accounted for 23.1% (n = 15), plants for flowers accounted for 21.5% (n = 14), and plants for fruits accounted for 3.1% (n = 2), suggesting that most residents used foliage plant types for leaves (

Table 6. Plant types based on appreciation parts in residential spaces.

Appreciation Part	Leaves	Flowers	Fruit	Color or Pattern of Stems	Total
Total	64 (98.5)	14 (21.5)	2 (3.1)	15 (23.1)	65 (100.0)

Note. Multiple Response, N (%).

).

As public spaces such as living rooms provide the advantages of viewing the growth of plants and plant landscapes, it is assumed that plants were mainly placed in public spaces. In addition, as there is limited space for installing interior landscapes in residential spaces, it is assumed that there were many container types that are relatively easy to install. Although interior landscapes combining container and hanging styles were present, the rate was low. The development of diverse interior landscape techniques could lead to the revitalization of the interior landscape design in residential spaces. These findings were partially consistent with Kim and Lee [37], who found that plants in interior landscapes were mostly located on verandas and not in such private spaces, such as bedrooms or bathrooms. In addition, the findings were in line with Lee et al. [4], who argued that spatial plans using plants accounted for the largest (64.9%) portion of interior landscapes. Likewise, Pérez-Urrestarazu et al. [11] demonstrated that plants were the most widely (86.1%) used element indoors and outdoors. The arrangement and pattern of the interior landscape tended to be uniformly designed in residential spaces.

4.3. Environmental Characteristics of the GI in Interior Landscapes of Residential Spaces

We investigated perceived GI ranges and objective and subjective GIs to examine the environmental characteristics of the GI in interior landscapes of residential spaces.

GI ranges in residential spaces are presented in

Table 7. GI ranges in residential spaces N (%).

Classification	Only Leaves	Included Branches and Stems	Included Containers	Included Shelves and Display Stands	Total
Total	1 (1.5)	8 (12.3)	31 (47.7)	25 (38.5)	65 (100.0)

. Of the total, 47.7% of the respondents thought that containers should be considered in GI, 38.5% included shelves and display stands, 12.3% included branches and stems, and 1.5% included only leaves. The GI generally estimates the proportion of plant parts in the entire field of view; however, the participants considered containers and even display shelves as green spaces. Therefore, when measuring the GI in residential spaces, more extended GI than the general concept could be calculated by including containers.

Objective GI determined based on photo analysis and subjective GI perceived by residents are presented in

Table 8. GI current state in residential spaces.

Classification			N	M (SD)	p
Housing Types	detached houses	objective GI	8	5.54 (3.05)	0.015 *
		subjective GI	8	18.88 (11.56)
		total	16	12.21 (10.68)
	multi-unit dwellings	objective GI	57	11.07 (16.20)	0.002 **
		subjective GI	57	14.74 (14.29)
		total	114	12.91 (15.32)
Spatial Composition	public spaces	objective GI	47	7.17 (9.42)	0.000 ***
		subjective GI	47	14.77 (12.55)
		total	94	10.97 (11.68)
	functional spaces	objective GI	18	18.82 (23.18)	0.899
		subjective GI	18	16.50 (17.52)
		total	36	17.67 (20.28)

Note. * p < 0.05, ** p < 0.01, *** p < 0.001; Mann Whitney U-test.

Objective GI was calculated including containers based on the participants’ perceived GI range in residential spaces.

Objective GI had an overall average of 10.39%, with 7.17% for public spaces and 18.82% for functional spaces. The interior landscape in functional spaces, such as utility rooms and verandas, was higher than in public spaces, such as kitchens (p = 0.006). The GI in functional spaces was high, as spaces were smaller than public spaces; however, most plants were large, or the number of containers was high. Due to the presence of drainage facilities, such as water supply and drains, in functional spaces, plant management was easy, and it was possible to link with other spaces, which could produce a borrowed scenery effect.

Subjective GI had an overall average of 15.25%. The paired-sample T-test between objective and subjective GI revealed no significant difference. Furthermore, satisfaction with the current interior landscape was found to be high at 4.32 points (on a five-point Likert scale, 1 = Strongly disagree, 2 = Disagree, 3 = Normal, 4 = Agree, 5 = Strongly agree). A previous study [16] demonstrated that a GI of approximately 10–20% was generally appropriate for interior landscapes and resulted in satisfaction for the residents.

In addition, the difference between objective and subjective GI was examined based on housing types and spatial composition. The subjective GI was 18.88% and objective GI was 5.54% for detached houses. For multi-unit dwellings, the subjective GI was 14.74% and objective GI was 11.07%, indicating that the subjective GI was higher.

For public spaces, the subjective GI was 14.77% and objective GI was 7.17%. For functional spaces, the objective GI was 18.82% and subjective GI was 16.50%.

These results indicated that residents’ perceived GI was higher than the objective GI. In particular, for detached houses, the greenery visible in the nearby outdoor space likely contributed to the subjective GI, even if there were not many landscape plants in the indoor space. As there was a difference in perception between the actual landscape plan and the volume of landscaping, further research is required in the future. This would assist in setting the direction of effective and appropriate landscape design in residential spaces.

4.4. Preference Characteristics of the Introduced Interior Landscape in Residential Spaces

To identify preferences in interior landscapes in residential spaces, we categorized the effect of introducing interior landscapes, the purpose of currently present interior landscapes, satisfaction level with current interior landscapes, reasons for satisfaction or dissatisfaction, preferred spaces for introducing interior landscapes, and preferred plants for interior landscapes (

Table 9. Effect of interior landscapes in residential spaces.

Effect of Interior Landscapes		M (SD)
1	spatial vitality	4.35 (0.76)
2	visual beauty	4.26 (0.89)
3	psychological stability	4.32 (0.75)
4	division of indoor space and boundary division	3.08 (1.11)
5	temperature and humidity control of the indoor space, and air quality improvement and noise reduction	3.08 (0.96)
6	higher interest in plants	4.02 (0.96)

Note. five-point Likert scale, 1 = Strongly disagree, 2 = Disagree, 3 = Normal, 4 = Agree, 5 = Strongly agree.

,

Table 10. Purposes of introducing the interior landscapes in residential spaces N (%).

Classification	Air Purification	Psychological Comfort	Visual Beauty	Healing Effect	Other	Total
Total	6 (9.2)	27 (41.5)	20 (30.8)	6 (9.2)	6 (9.2)	65 (100.0)

,

Table 11. Reasons for satisfaction or dissatisfaction with current interior landscapes N (%).

Classification	Satisfaction						Dissatisfaction		Total
	Air Purification	Psychological Comfort	Visual Beauty	Healing Effect	Gardening Activities	Other	Management Difficulties	Lack of Time
Total	-	24 (36.9)	11 (16.9)	5 (7.7)	13 (20.0)	5 (7.7)	5 (7.7)	2 (3.1)	65 (100.0)

and

Table 12. Preferred locations for interior landscapes in residential spaces N (%).

Classification	Public Spaces	Functional Spaces			Total
	Living Rooms	Living Room Verandas	Couple’s Bedroom Verandas	Other Verandas
Total	36 (55.4)	25 (38.5)	2 (3.1)	2 (3.1)	65 (100.0)

).

Regarding the effect of interior landscapes, on a five-point Likert scale, spatial vitality was 4.35 (SD = 0.76), psychological stability was 4.32 (SD = 0.81), visual beauty was 4.26 (SD = 0.89), higher interest in plants was 4.02 (SD = 0.96), and division of indoor space and boundary division, temperature and humidity control of the indoor space, and air quality improvement and noise reduction were 3.08 (SD = 0.96) each (Table 9).

The purposes of introducing the interior landscapes were psychological comfort (41.5%, 27 places), visual beauty (30.8%, 20 places), air purification and healing effect, and other (9.2%, 6 places). Plants were mainly introduced for psychological stability and aesthetic effect. Among other reasons, plants were introduced due to family member preference (4 places), for humidity control (1 place), and utilization as food ingredients (1 place) (Table 10).

By installing the landscape, the residents expected to create lively and beautiful interior spaces and to feel psychologically stable.

On a five-point Likert scale, satisfaction with current interior landscapes was 4.37 point (SD = 0.86), indicating high satisfaction for 58 out of 65 places. Reasons for satisfaction or dissatisfaction with current interior landscapes are presented in Table 11. Reasons for satisfaction were psychological comfort (36.9%, 24 places), a sense of accomplishment (reward) of gardening activities (20.0%, 13 places), and visual beauty (16.9%, 11 places), whereas reasons for dissatisfaction were management difficulties (7.7%, 5 places) and lack of time (3.1%, 2 places).

The participants’ preferred locations for interior landscapes are presented in Table 12. The participants preferred public spaces (55.4%, 35 places), particularly living rooms, and functional spaces (44.6%, 29 places), particularly living room verandas (38.5%, 25 places), which were connected to the living room, a public space.

The preferred types of interior landscape plants are presented in

Table 13. Preferred types of interior landscape plants in residential spaces N (%).

Classi-Fication	Bulbous Crops	Foliage Plants	Cacti & Succulents	Aquatic Plant & Hydrophyte	Orchids	Carnivorous Plants	Herbs	Flowering Plants	Total
Total	3 (4.6)	34 (52.3)	9 (13.8)	1 (1.5)	3 (4.6)	1 (1.5)	9 (13.8)	5 (7.7)	65 (100.0)

. Foliage plants accounted for 52.3% (34 places), cacti and succulents accounted for 13.8% (9 places), herbs accounted for 13.8% (9 places), flowering plants accounted for 7.7% (5 places), bulbous crops and orchids accounted for 4.6% (three places) each, and aquatic plant, hydrophyte, and carnivorous plants accounted for 1.5% (one place) each. Therefore, the majority of the participants preferred foliage plants.

5. Discussion

As interest in a healthy and comfortable indoor space has increased, there has been a growing interest in interior landscapes to create pleasant environments by introducing natural elements into indoor spaces and promote mental health and psychological stability. Interior landscapes are used to relieve stress and obtain psychological stability in residential spaces. However, despite the numerous positive effects of interior landscape, the interior landscape design in residential spaces continues to be used in a standardized manner only in limited spaces.

Therefore, this study examined interior landscapes and characteristics of the GI in residential spaces and surveyed residents, including their preferences for interior landscape planning. This study aimed to explore the direction to effectively create and revitalize the interior landscape in residential spaces, which is currently utilized in a limited and passive manner.

The results indicated that many interior landscape arrangements included plants valued for leaves placed in containers using soil in public spaces. The residents mainly utilized the living rooms, with reasons including time spent indoors, indoor activities, aesthetic effect of landscaping, and ease of landscape management. As watering, soil management, and movement are convenient, large and small pots were mainly utilized for creating the landscape.

In addition, the GI is generally calculated based on areas of leaves, flowers, branches, and stems of trees. However, the perceived GI range, which is the area of green plant parts indoors, of the participants included plant parts and pots containing plants. This indicates that the GI range in indoor spaces can be calculated differently from the common calculation of GI in the outdoor horizontal space. The balanced design between plants and containers is important when planning interior landscapes.

Furthermore, the participants’ subjective GI (approximately 15% on average) was approximately 5% higher than the objective GI that was calculated based on photos (approximately 10% on average). Therefore, the green space was perceived to be larger than the actual number of plants, suggesting that the natural light inflow through the glass window and view can affect the recognition of indoor GI. A previous study found that when indoor plants were placed in windows, both the effects of reducing physiological stress and the level of psychological anxiety were obtained [11,38,39]. The present results indicated that plants were mainly installed in the living room and veranda. In Korean residential spaces, living rooms and verandas generally have larger and wider windows than other spaces, such as bedrooms and kitchens; therefore, it is easy to connect with the outdoor environment. There was likely a higher effect of interior landscapes in these places. Kim and Lee [40] found that there were different preferences for green space rates in underground and above-ground spaces with light in subway stations. GI preference characteristics based on the presence and size of windows in residential spaces should be examined in the future.

In terms of the effect, purpose, and satisfaction of the introduction of the interior landscape in the residential space, psychological stability and visual beauty were found to be high for all questions. This indicates that the introduction of indoor plants had psychologically positive effects. Moreover, a previous study found that experiencing visual beauty through landscape plants had the effect of relieving tension psychologically [11,41]. The combined psychological and aesthetic effects of the interior landscape provide greater satisfaction for the residents.

Foliage plants on the veranda connected to the living room, combining public and functional spaces, were found to be the most preferred. Foliage plants in containers were the most common in the living room, and the preferred spaces and methods were almost identical. In Korean residential spaces, the living room encompasses the lives of all family members and is the central space of the house. Therefore, the spatial importance is high, the living room is mostly located in the south, and the design is emphasized. Therefore, residents preferred to install interior landscapes in living rooms to improve value and interior design. In addition, the living room and living room veranda were advantageous as they provided convenience and the landscaping effect, such as appreciating plants and securing natural light. Foliage plants were likely preferred because they have a growth habit that tolerates relatively high temperatures and low luminance [42] compared to other flower plants, due to drought resistance and shade endurance. A previous study [29] indicated that foliage plants, mint, basil, and begonia had positive effects on the psychological and physiological responses of users.

6. Conclusions

This study confirmed several positive effects of interior landscapes in residential spaces, including the connection between indoor and outdoor environments, the aesthetic effect, and the environmental effect. In addition, this study identified the direction of the interior landscape design in the residential space by surveying the residents’ preference for and perceived GI of interior landscapes.

In order to promote interior landscapes in the residential space, introducing various planting methods and soil alternatives with easy landscaping is expected to provide more pleasant landscaping effects in residential spaces without restrictions on the locations of landscaping.

Introducing plants with easy-to-manage designs and plant types, development and distribution of pots that make growing plants easy, such as vegetation biofilters, and the development of diverse planting methods would likely contribute to expanding the passive introduction of interior landscapes and increase the positive effects of the landscape design. By activating landscape in interior space design, a pleasant and healthy environment will be created improving the psychological and physical health of residents. In the future, more detailed and diverse plans for interior landscapes in residential spaces should be created by constructing and testing experimental models for residential spaces based on the GI. The limitations of this research are as follows. First, this study has significance in that it calculated indoor GI including flowerpots according to the characteristics of the introduction of interior landscapes in the residential space and the range of residents’ perception for indoor GI. However, comparison of GI between previous studies may be limited due to differences in the range of GI calculation from previous studies. Research on indoor GI according to the inclusion of flowerpots should be conducted in the future.

Second, when introducing interior landscape in the residential space, in addition to the housing type, space composition, and interior landscaping method, GI can be planned according to the presence and size of windows, the presence of outdoor landscaping, and the degree to which outdoor landscape is introduced into the indoor space. Thus, GI research according to various environmental characteristics should be carried out in the future.

Third, user evaluation should be performed by implementing an interior landscaping model according to the GI of the residential space in the future. Through this process, it is expected that it will contribute to establishing a more specific and feasible plan for implementing the interior landscape in the residential space.