Research subjects (participants) were recruited from the Department of Rehabilitation and Independence (Specialized Division of Developmental Disabilities) at N University, located in Cheonan. The department, targeting people with developmental disabilities, is divided into tracks based on the type of work they are interested in. Students enrolled in the Horticulture Track and taking a horticulture course were given an explanation about the greenterior program and how they could participate in the program as an exercise tied to the course. Written informed consent was obtained from students and their parents who agreed to participate in the program, and the program was implemented, targeting only such students. In addition, IRB verification of the program (IRB-Nazarene University-2023-37) was completed through deliberation by the N University Bioethics Committee. Class A, the experimental group, consisted of 15 participants who took the plant-related practical course. For Class B, the control group, although 17 students were selected from the same Specialized Division of Developmental Disabilities who did not participate in the program and instead took other courses that focused on general theory at the same time, only 15 students ultimately participated, as two who withdrew during the consent form completion process were excluded. The participants met the following criteria: Both participants and their guardians provided informed consent to participate in the program; the students were college students who met N University's academic ability standards and had a borderline or mild developmental disability (Level 3 Developmental Disability); and the participants held a registration card or welfare card for the disabled as per Article 32 of the Act on the Welfare of Persons with Disabilities. The gender composition was 11 males and 4 females for Class A, and 12 males and 3 females for Class B. The research personnel included a facilitator with a doctoral degree in horticulture, an assistant facilitator with a master's degree in rehabilitation, and a lecturer who majored in art.

The program consisted of 10 sessions with a three-stage structure, as follows. Taking into account cognitive, affective, and psychomotor/kinesthetic domains based on familiarity components, in the introduction stage of each session, space-related storytelling was used to establish rapport. In the development stage, greenterior items were produced based on what was understood through the storytelling. In the finishing stage, the focus was on arranging the space and utilizing the items. The program was scheduled for 10 sessions from October to November 2023 to allow for full implementation in connection with the course, excluding periods such as exams and orientation field training in the academic schedule. The program was intended not only to help CSDDs experience it and develop correct values about plants and their surroundings, but also to make it easier for them to understand space-related things through storytelling based on their interaction as speakers and listeners, thereby fostering their interest in the living environment and developing their design skills using plants. To this end, the program, with the structure of introduction, development, and finishing steps was designed in detail in consultation with the expert group (FGI), as shown in Table 1.

The content of the program was designed to enhance comprehension of space and plants by incorporating storytelling into each session. Sessions 1–3 covered the cognitive domain, which encompassed fundamental knowledge and general understanding of plants. Sessions 4–6, which comprised the middle stage, focused on allowing participants to express their emotions in the affective domain and become familiar with plants by creating aesthetic interior ornaments and applying them to space. Sessions 7–9 enhanced the psychomotor/kinesthetic domain through cooking activities that promote physical health, and creating works that require body coordination. Each session lasted for 2 hours, with an introduction (storytelling and preparation for practice) in the first class, and development (practice in making interior decorations) and finishing (space arrangement, presentation and cleanup) in the second class. Easy-to-access design techniques, such as printmaking, collage, image drawing, and miniature model production among art media, were appropriately used considering those who have difficulty drawing.

While conventional horticultural education focuses on plant cultivation and hands-on activities, this program, a greenterior program tailored to the needs of CSDDs, offers a unique approach through the following features. The program sought to improve participants' cognitive understanding by having them watch videos of plant use cases applied to different spaces and engage in conversations with researchers about each space in a storytelling manner. Furthermore, it encompasses the steps of having them create greenterior decorations and arrange them in spaces. Considering the cognitive, affective, and psychomotor/kinesthetic capabilities related to the detailed domains of plant familiarity in Table 2, a focus group of experts was consulted to obtain advice for this study. A review was also requested from professionals in the fields of horticulture, art, and rehabilitation with consideration of CSDDs' understanding. In this study, the classification of the detailed domains of plant familiarity into cognitive, affective, and psychomotor/kinesthetic tendencies was adapted for CSDDs, based on Lee's (2012) and Chung's (2020) classification criteria for plant familiarity of elementary school students. Table 2 shows the specifics of each session. The cognitive domain was divided into growing conditions, plant classification, and increased integrated thinking. The affective domain included emotional stability, stress management, and character development. The psychomotor/kinesthetic domain was divided into environmental and dietary effects. The specifics were created by referring to the data suggested by Bae and Park (2018) and considering the participant's performance abilities. During Session 1, participants were introduced to different types of plants through storytelling about the wonderful world of plants. They then observed a collected and dried Neprolepis obliterata, and used acrylic paint and a printmaking technique called planographic printing to stamp its shape and create hanging scrolls for wall decoration. In Session 2, after being presented with a story about how a house is made, participants constructed a house model using a kit and created plant sculptures using floral foam and Aspidistra elatior to arrange them in the model. This activity enhanced their understanding and integrated thinking about the relationship between space and plant sculpture. During Session 3, participants were presented with a story about the four seasons paired with trees to help them understand the four seasons from a plant physiological perspective and create color images of the four seasons with colored paper on canvas. This activity affected the cognitive domain by helping students understand growing conditions. Thus, framed canvas works were created using colored paper through a collage technique. During Session 4, after appreciating the stories of urban farmers through storytelling, participants created a mini garden using recycled materials that were discarded in urban areas. This activity enabled them to understand the benefits of urban gardens, and resource recycling. During Session 5, after enjoying storytelling about theme gardens and party decorations, participants created placemats using a flower-pressing technique, which can be used as table decorations for parties. During Session 6, participants were presented with a story about air purification in residential spaces and indoor gardens to aid their comprehension of terrarium principles. They were then tasked with creating a model of a residential space, and a terrarium to serve as decoration for a small indoor area. During Session 7, participants watched a video showcasing the botanical garden cafe and listened to a story about plants and health. They then created and tasted canapés with edible flowers and fruits, as well as vegetable salad. They also recreated a dessert cafe, a commercial space, and presented ideas for improving eating habits to promote physical health. During Session 8, participants were presented with a storytelling about fine dust and air purification. They were also provided an explanation of the effects of wall gardens for air purification, along with relevant examples. Finally, they were asked to create a framed moss topiary garden. During Session 9, participants were introduced to community gardens through a story about gardens that people wanted to share. They collaborated in groups to draw a blueprint for a garden they wanted to share, and then cooperatively constructed it. Notably, throughout the design process, they actively communicated through group discussions. In Session 10, participants presented a story about their dream garden they would like to have in the future, and arranged their completed works in the form of a mini garden.

Before the analysis, the final population size was 15 for the experimental group and 15 for the control group. Since the population size of each group was in the range of 10 to 30, the normality was checked. As a result, the following tests were used to confirm normality: in the Koimogorov-Smimov test, p = .167 > .05 for the experimental group and p = .200 > .05 for the control group; in the Shapiro-Wilk test p = .183 > .05 for the experimental group and p = .615 > .05 for the control group. Therefore, a paired t-test could be performed.

Table 3 shows the analysis results of the t-test performed to verify the homogeneity of the two groups, the control and the experimental groups, before the implementation of the greenterior program. As the three sub-domains of plant familiarity assessment in this study, the cognitive domain (p = .172), the affective domain (p = .066), and the psychomotor/kinesthetic domain (p = .165), as well as the overall plant familiarity were all p > .05, there was no significant difference in both groups. The p-value of Levene's test for homoscedasticity was p = .801 > .05 for the cognitive domain, p = .211 > .05 for the affective domain, p = .084 > .05 for the psychomotor/kinesthetic domain, and p = .052 > .05 for plant familiarity. In other words, the control and the experimental groups were found to be homogeneous, so this study could proceed.

After implementation of the greenterior program, the three sub-domains of the plant familiarity assessment (cognitive, affective, and psychomotor/kinesthetic domains) and the overall plant familiarity of the control and experimental groups were analyzed using a paired t-test. For the control group, it was found that there were no significant differences in any of the domains: cognitive domain (p = .294), affective domain (p = .856), psychomotor/kinesthetic domain (p = .130), and plant familiarity (p = .795). Meanwhile, the experimental group showed statistically significant differences in all sub-domains after the greenterior program: cognitive domain (p = .000), affective domain (p = .000), and psychomotor/kinesthetic domain (p = .000), and plant familiarity (p = .000). In other words, the greenterior program had a positive effect on both plant familiarity and all sub-domains of CSDD.