Effects of a Cognitive Behavioral Therapy-Based Agro-Healing Horticultural Therapy Program on Depression and EEG in High-Risk Groups for Depression

Article information

J. People Plants Environ. 2026;29(2):225-241

Publication date (electronic) : 2026 April 30

doi : https://doi.org/10.11628/ksppe.2026.29.2.225

Sang-Mi Lee ¹

, Yun-Jeong Kang ¹^,

, Eun-Ju Song ², Sun-Jin Jeong ¹, Jiwon Moon ¹, Yeseul Jo ¹, Sena Choi ¹, In-Kyoung Hong ¹, Youngdo Shim ¹

¹Researcher, Urban Agriculture Research Division, National Institute of Horticultural and Herbal Science, Rural Development Administration, Wanju-gun, Jeollabuk-do 55365, Republic of Korea

²Professor, Department of Nursing, Wonkwang University, Iksan 54538, Republic of Korea

^*Corresponding author: Yun-Jeong Kang, adelogarden@naver.com, https://orcid.org/0009-0002-8687-3365

First author: Sang-Mi Lee, sangmilee@korea.kr, https://orcid.org/0000-0003-1049-4705

This study was supported by the 2025 Horticultural and Herbal Science Program of the National Institute of Horticultural and Herbal Science of the Rural Development Administration (RS-2021-RD009877).

Received 2026 February 3; Revised 2026 March 7; Accepted 2026 April 2.

Abstract

Background and objective

This study aimed to empirically evaluate the effectiveness of an agro-healing program that integrates the plant life cycle with cognitive-behavioral strategies as an emotional and cognitive intervention for individuals at high risk of depression. Specifically, a cognitive behavioral therapy (CBT)-based agro-healing horticultural therapy program was applied to assess its effects on both psychological and physiological outcomes, including depressive symptoms and electroencephalogram (EEG) changes.

Methods

Conducted in ten weekly 90-minute sessions, the horticultural activity-based program was conducted by incorporating five core components of cognitive-behavioral strategies—identification of cognitive distortions, problem-solving, socialization, reward, and cognitive restructuring—into the stages of the plant life cycle, including sowing, cultivation, harvesting, and utilization.

Results

In the control group, which received only conventional psychiatric treatment, scores for interpersonal problems—a subdomain of depression—significantly increased following the intervention. In contrast, the experimental group, which participated in the CBT-based agro-healing horticultural therapy program in addition to conventional care, demonstrated an overall reduction in depression levels. Statistically significant improvements were observed in somatic retardation, interpersonal problems, depressive affect, and total depression scores. Moreover, compared with the control group, the experimental group exhibited significantly greater reductions across these domains. These findings suggest that vulnerability to depression extends beyond emotional symptoms and is structurally associated with impairments in social cognition, interpersonal functioning, and relationship maintenance.

Conclusion

The findings indicate that an agro-healing horticultural therapy program integrating cognitive-behavioral strategies into plant-based activities may effectively reduce depressive symptoms and promote psychological stability in individuals at high risk of depression. Furthermore, this study is meaningful in that it provides integrated evidence based on both psychological scales and EEG measures.

Keywords: depression; gardening; healing; EEG; CBT

Introduction

In contemporary society, mental health has emerged as a critical global public health issue that extends beyond individual-level concerns. According to the World Health Organization (WHO, 2022), the prevalence of anxiety and depression increased by approximately 25% worldwide following the COVID-19 pandemic. In South Korea, 9.7% of individuals aged 12 years and older reportedly experienced depressive symptoms within the past year, while schizophrenia affects approximately 1 in 100 individuals (National Center for Mental Health, 2023). These prevalence rates continue to rise as socio-structural factors, such as emotional isolation and economic instability, interact in complex ways in the post-pandemic era (Byun, 2024). Notably, individuals in the high-risk group for depression have been reported to have approximately twice the likelihood of developing major depressive disorder compared to the general adult population (Lee et al., 2019).

Among interventions for this high-risk population, pharmacotherapy has been widely used and can be effective for short-term symptom relief. However, it presents several limitations, including adverse effects associated with long-term use, high relapse rates, treatment resistance, and an increased risk of suicidal ideation. Moreover, its effectiveness in terms of functional recovery and social reintegration remains limited (Ha et al., 2020). In patients with major depressive disorder, improvements in clinical symptoms do not necessarily translate into recovery of daily functioning; many individuals continue to experience psychosocial functional impairment even after treatment (Yang et al., 2022). Moreover, although antidepressant treatment may alleviate emotional symptoms, recovery in social functioning and interpersonal relationships is often delayed (Kennedy et al., 2007), and such treatments frequently fail to effectively address functional impairment or facilitate social reintegration (Nunez et al., 2022). These limitations underscore the need for diverse complementary approaches, particularly for high-risk groups, where non-pharmacological and psychosocial interventions are increasingly recognized as alternatives that can enhance autonomy and psychological acceptance.

Non-pharmacological approaches for individuals at high risk of depression include problem-solving therapy, behavioral activation, and cognitive behavioral therapy (CBT), with CBT reported to be one of the most effective approaches (Hao et al., 2023). CBT is a widely utilized evidence-based psychotherapy that aims to modify emotional needs and maladaptive behaviors through techniques such as cognitive restructuring, problem-solving, social skills training, and reinforcement strategies (Weaver et al., 2014). It has demonstrated significant efficacy in improving symptoms across a wide range of mental health conditions, including anxiety, depression, sleep disorders, and eating disorders; its therapeutic strength lies in its integrated approach to both cognitive and behavioral domains (Hofmann et al., 2012). CBT has been broadly applied to individuals with a broad range of symptoms worldwide, extending beyond traditional psychiatric disorders to include stress-related and psychosomatic conditions (Nakao, Shirotsuki, and Sugaya, 2021). More recently, CBT has evolved into digitally delivered formats, including online and mobile-based self-guided interventions, offering a useful approach to address disparities in mental health resources between countries. Furthermore, Dorsey et al. (2020) demonstrated that CBT can achieve high levels of effectiveness even when delivered by trained lay counselors in communities, highlighting its adaptability across cultural contexts and diverse nations and populations.

In parallel, agro-healing—a nature-based therapeutic approach—has emerged as a complementary strategy for addressing various mental health concerns. Defined as a distinctive concept in South Korea, agro-healing refers to an integrative intervention that promotes emotional and psychological recovery through agriculture-based activities, including care farming, horticultural therapy, animal-assisted therapy, insect-mediated therapy, and rural wellness tourism. Beyond recreational engagement, agro-healing utilizes agricultural processes—such as cultivation, harvesting, and processing—as therapeutic media for facilitating emotional recovery and behavioral change. It represents a holistic intervention approach that incorporates multisensory stimulation, physical activity, and social interaction (Rural Development Administration, 2024b). In South Korea, the Act on Research, Development, and Promotion of Healing Agriculture (hereinafter referred to as the Agro-Healing Act) was enacted in 2021, followed by the establishment of The 1st Comprehensive Plan for Healing Agriculture Research, Development, and Promotion (2022–2026) (Rural Development Administration, 2022). These initiatives have enabled the systematic, nationwide promotion of agro-healing. Agro-healing encompasses activities that utilize various agricultural and rural resources to support health promotion and psychological and emotional recovery. The scope of agro-healing extends beyond plant-based activities, such as cultivating vegetables and flowers, to include livestock rearing and the utilization of forest and rural cultural resources. Its primary objective is to facilitate the health recovery of both individuals seeking a healthier and happier lifestyle and those in need of medical or social therapeutic intervention. A key distinction from conventional agriculture lies in its purpose: agriculture is employed as a therapeutic means rather than an end in itself (Rural Development Administration, 2024b). Research and development in agro-healing initially emerged from horticultural therapy led by the National Institute of Horticultural and Herbal Science under the Rural Development Administration. Since 2013, the National Institute of Agricultural Sciences has expanded research into insect-mediated therapy and rural wellness tourism-based interventions, while the National Institute of Animal Science has focused on animal-assisted therapy (Rural Development Administration, 2024b). Previously, related concepts were developed independently across institutions; however, these were unified under the term “agro-healing” through the enactment of the Agro-Healing Act in 2020, enabling the establishment of an integrated policy system (Lee et al., 2025).

Research on horticultural therapy or therapeutic horticulture has been actively conducted. In particular, group-based horticultural activities have been shown to significantly reduce depressive symptoms and promote emotional stability (Briggs et al., 2023), and they are effective in alleviating depression and improving psychological well-being among older adults with dementia (Kim, 2023). Meta-analytic evidence further indicates that horticultural therapy significantly improves psychological stress indicators compared to control conditions (Lu et al., 2023). Social and therapeutic horticulture have demonstrated a highly significant effect in reducing depressive symptoms and moderate, statistically significant effects in alleviating anxiety (Wood, 2025). Furthermore, horticultural therapy programs have been reported to positively affect autonomic nervous system activity and psychological stability in patients with cancer (Oh, 2025). These findings suggest that horticultural therapy can serve as a promising alternative or adjunctive intervention for reducing depression and anxiety (Wood, 2025).

However, existing agro-healing and horticultural therapy programs remain centered on emotional support and fall short of fostering cognitive or behavioral changes. Consequently, they face structural limitations in addressing cognitive distortions and irrational behaviors. Although previous research has shown that horticultural therapy programs based on relaxation, social support, and cognitive behavior strategies positively affects psychosocial outcomes (e.g., improved quality of life, reduced stress, and decreased depression) in cancer patients (Lee et al., 2016), these interventions have often relied on passive, indoor-based activities. Integrating CBT—a field of psychotherapy— with agricultural practices linked to the life cycle of plants may enhance therapeutic outcomes by fostering synergistic interactions between immersive sensory experiences in nature and structured psychological interventions.

Accordingly, this study aimed to design and implement a program that integrates core components of CBT into the plant life cycle, enabling individuals at high risk of depression to naturally reflect on and regulate their cognitive, emotional, and behavioral patterns through active participation in horticultural activities. The effectiveness of the program was evaluated by examining changes in depressive symptoms and associated electroencephalogram (EEG) patterns.

Furthermore, given that horticultural therapy is conceptualized as a subdomain of agro-healing in South Korea, this study adopts the term “agro-healing horticultural therapy” to emphasize its theoretical and practical positioning within the broader agro-healing framework. This term will be used consistently throughout the study.

Research Methods

Research Design

This study aimed to evaluate the effects of a CBT-based agro-healing horticultural therapy program on depressive symptoms and electroencephalographic (EEG) activity among high-risk individuals with mental disorders receiving inpatient or outpatient psychiatric care. The intervention integrated five core components of cognitive behavioral therapy (CBT)—identifying/recognizing of cognitive distortions, problem-solving, socialization, reward/reinforcement, and cognitive restructuring—into the plant life cycle stages of propagation, cultivation/management, harvesting, and utilization. The program was delivered once weekly for 90 minutes per session over a total of 10 sessions. A quasi-experimental, non-equivalent control group pretest-posttest design was employed, comprising a control group receiving conventional psychiatric care and an experimental group receiving both conventional care and the CBT-based agro-healing horticultural therapy intervention.

Participants

The study was conducted in two phases: September–November 2023 and April–July 2024. Participants were 33 high-risk individuals with depression recruited from inpatients and outpatients at M Psychiatric Institution in W-gun, J-do, South Korea. The control group (n = 16) received conventional psychiatric care, whereas the experimental group (n = 17) participated in the CBT-based agro-healing horticultural therapy program in addition to conventional care. To minimize treatment diffusion and contamination, and to reduce potential researcher-induced bias, Ward A was assigned to the experimental group and Ward B to the control group. This allocation was determined in consultation with attending psychiatrists, psychiatric nurses, and mental health social workers. The two wards were located on separate floors, limiting physical interaction. Both wards operated comparable routine programs, including social skills training, activities of daily living (ADL) training, music therapy, and art therapy (Fig. 1). In addition, differing schedules for outdoor activities (e.g., walking) further reduced the likelihood of intergroup contact. Efforts were made to minimize treatment diffusion and contamination throughout the study. For the second phase, participants recruited from Ward A were restricted to those without prior participation in the first phase.

Fig. 1

Implementation of the CBT-based agro-healing horticultural therapy program.

Inclusion criteria were as follows:

1) Individuals classified as high-risk for depression, defined as a Beck Depression Inventory (BDI) score ≥ 17 (Park, 2020);
2) Individuals who understood the study purpose and provided voluntary informed consent;
3) Individuals capable of reading and completing the questionnaire without communication difficulties

Ethical Consideration

This study was approved by the Institutional Review Board (IRB) designated by the Ministry of Health and Welfare of South Korea (Approval No.: 2023-0752-001). Prior to data collection, the study objectives and program procedures were explained to all participants in both groups to ensure ethical compliance and the protection of participants’ rights. Participants were informed that there were no anticipated risks or adverse effects associated with participation and that the collected data would be used solely for research purposes. Confidentiality was ensured through anonymized data processing, and participants were informed of their right to withdraw from the study at any time during the program. Written informed consent was obtained from all participants who voluntarily wished to participate in the study.

Cognitive Behavioral Therapy-Based Agro-Healing Horticultural Therapy Program

A cognitive behavioral therapy (CBT)-based agro-healing horticultural therapy program for individuals at high risk of depression was designed based on core CBT principles. The program was developed through a collaborative design process involving two agricultural researchers (horticultural therapy specialists with formal training in CBT theory), one certified agro-healing specialist, one psychiatrist specializing in CBT, one professor of psychiatric nursing, and one mental health social worker. Drawing on the plant life cycle—from sowing to harvesting and utilization—the program was structured around key CBT strategies, including identification of cognitive distortions, problem-solving, reinforcement, socialization, and cognitive restructuring (Beck, 2011; Dobson, 2010; Hofmann, 2012; Rural Development Administration, 2024a).

Each session lasted 90 minutes and was conducted within the participating hospital. The program was structured as a 10-session, time-sequenced model to encompass the full horticultural life cycle (propagation, cultivation, harvesting, and utilization), while also accounting for participants’ capacity for sustained engagement and institutional care conditions. Each session comprised approximately 60 minutes of horticultural activities—including 15–30 minutes of active sunlight exposure—followed by 30 minutes of worksheet completion and reflection sharing. Participants in the experimental group engaged in the CBT-based agro-healing horticultural therapy program in addition to conventional ward-based interventions, including social skills training, activities of daily living (ADL) training, music therapy, and art therapy (Fig. 1). The control group participated only in the conventional ward programs and did not receive the agro-healing intervention.

In Session 1, participants engaged in sowing leafy vegetables and flowering plants in trays, along with direct seeding of root vegetables (radish), while a CBT-based intervention focused on identifying cognitive distortions, such as “Will they even sprout?”, “Plants always die when I grow them,” or “I’m not good at growing plants.”

In Session 2, participants practiced propagating herbs and foliage plants through cuttings, during which a problem-solving intervention encouraged them to explore adaptive strategies for managing life challenges by drawing parallels to how plant cuttings establish new roots for survival.

Session 3 implemented a socialization intervention during the transplanting of vegetables and flowers. Participants were introduced to the concept of companion plants that help each other grow and ward off pests and reflected on the meaning of companionship by identifying sources of social support and considering reciprocal growth within their interpersonal relationships.

In Session 4, a problem-solving intervention was implemented during pest management and plant training (growth guidance), in which participants explored strategies for actively addressing life challenges, such as overcoming and preventing their mental disorder, while also fostering empathic understanding of these experiences. In addition, a socialization intervention was incorporated into the plant training process to facilitate identification of supportive individuals whom participants could rely on during times of hardship.

In Session 5, participants transplanted seedlings sown in Session 1 into the garden. Problem-solving and socialization interventions were implemented using the concept of appropriate planting spacing as a metaphor for maintaining healthy interpersonal boundaries, with an emphasis on assertive communication as a means of promoting harmonious relationships with others.

In Session 6, a problem-solving intervention was implemented during fertilization, using the concept of essential nutrients for plant growth as a metaphor to encourage participants to explore the resources necessary for their personal growth and development. This was followed by a reinforcement intervention in which participants harvested root vegetables (turnips) sown in Session 1.

In Session 7, participants harvested flowers and prepared flower tea. This process facilitated the integration of reward, problem-solving, and socialization interventions; specifically, participants reflected on their diverse social roles and attitudes, symbolically represented by the pH-dependent color variations of the tea.

In Session 8, participants harvested flowers and created floral arrangements as self-gifts. By reflecting on experiences of success and achievement during this process, reward and cognitive restructuring interventions were implemented to promote positive self-perception and modify distorted cognitions.

In Session 9, participants used self-made pressed flowers to create tangible products, such as cards and coasters, thereby facilitating behavioral reinforcement through a sense of satisfaction and reward. By composing positive self-messages on the cards, participants experienced a sense of achievement, which supported cognitive restructuring by reframing negative self-perceptions into more positive ones. Furthermore, a socialization intervention was implemented by encouraging participants to envision sharing tea with others using their handmade coasters.

In Session 10, participants harvested vegetables and flowers from the garden to prepare a closing event featuring culinary dishes and floral decorations. By expressing emotions such as gratitude, satisfaction, and joy while celebrating program completion with their peers, participants engaged in a reward intervention. This process supported cognitive restructuring by facilitating a shift from negative to positive self-perception.

The CBT-based agro-healing horticultural therapy program was conducted twice: from September to November 2023 and from April to July 2024. Detailed contents of the program are presented in Table 1.

Table 1

Overview of the CBT-based agro-healing horticultural therapy program

Measurements

Beck Depression Inventory (BDI)

The Beck Depression Inventory (BDI), developed by Beck et al. (1961), is a self-report questionnaire and one of the most widely used instruments for assessing the severity of depression. In this study, the Korean adaptation of the Beck Depression Inventory-II (K-BDI-II) (Sung et al., 2008; Park et al., 2020) was employed to evaluate participants’ depression levels. Assessments were conducted at two time points: prior to the program and one day after its completion. The BDI-II is a revised instrument based on the diagnostic criteria for depressive disorders outlined in the DSM-IV and provides a comprehensive evaluation of cognitive, affective, behavioral, and somatic symptoms of depression. It consists of 21 items, each rated on a 4-point scale ranging from 0 to 3. Total scores range from 0 to 63, with higher scores indicating greater severity of depression. The reported Cronbach’s alpha for the BDI-II ranges from 0.90 to 0.93 (Beck et al., 1996); in the present study, Cronbach’s alpha was 0.83.

Center for Epidemiologic Studies Depression Scale (CES-D)

As an additional measure of depression, the Korean version of the Center for Epidemiologic Studies Depression Scale (CES-D), adapted by Chon, et al. (2001) from the original scale developed by Radloff (1977), was utilized. Assessments were conducted before the intervention and one day after its completion. The CES-D consists of 20 items encompassing four subdomains: somatic retardation, positive affect, interpersonal problems, and depressed affect. Items related to positive affect are reverse-scored. Responses are rated on a 4-point Likert scale, with higher total scores indicating greater depressive symptomatology. In the study by Chon et a l. (2001), Cronbach’s alpha was reported as 0.91; in the present study, it was 0.90.

Electroencephalography (EEG)

Electroencephalography (EEG) is a neurophysiological indicator closely associated with human cognitive and emotional states. It is a non-invasive technique that records electrical signals generated by neuronal processes via electrodes placed on the scalp. EEG data were collected at two time points: before the intervention and one day after its completion. Given the sensitivity of EEG signals to environmental conditions, recordings were conducted in a dedicated, windowless EEG laboratory at the National Institute of Horticultural and Herbal Science. The laboratory was maintained under controlled conditions, including temperature, humidity, and illumination, and was soundproofed. The room dimensions were 320 cm (L) × 250 cm (W) × 265 cm (H). In this study, EEG data were analyzed in conjunction with psychological measures rather than interpreted as standalone outcomes.

Specifically, theta (4–8 Hz) and alpha (8–12 Hz) bands are representative EEG indices associated with psychological stability, attention, and emotional response.

Relative theta power (RT) is a low-frequency brainwave band that increases during periods of focused attention, emotional recall, and mental imagery. It is particularly elevated during states of internalized attention, physiological attention related to emotional flow, emotional recall, and emotional engagement. Increases in RT have been associated with enhanced introspection and emotional stability, reflecting improved emotional resilience (Abid et al., 2025; Ertl et al., 2013; Cavanagh and Frank, 2014).

Relative alpha power (RA) is a mid-to-low frequency brainwave band generally associated with psychological stability, relaxation, and internally directed rest. RA has been shown to decrease significantly under conditions of psychosocial stress (Vanhollebeke et al., 2022). In contrast, RA increases during states of emotional stability, relaxation, low anxiety, and positive affect (Yoo et al., 2024; Lomas et al., 2015).

EEG data were acquired using the BIOS-ST system (Biobrain Inc., Daejeon, Korea), an 8-channel wireless wearable device (Fig. 2). This dry-sensor-based system enables reliable signal acquisition without skin abrasion or conductive gel. Electrodes were positioned at Fp1 (left frontal lobe), Fp2 (right frontal lobe), T3 (left temporal lobe), T4 (right temporal lobe), O1 (left occipital lobe), O2 (right occipital lobe), Fz (medial frontal lobe), and Pz (medial parietal lobe). The frontal regions (Fp1, Fp2) are associated with emotion regulation and cognitive control and are therefore considered key sites in studies of depression and emotional states (Davidson, 1998; Thibodeau et al., 2006). In contrast, the temporal regions (T3, T4) are known to reflect brain activity underlying emotional information processing and emotion-related cognitive processing (Knyazev, 2007; Davidson and Irwin, 1999).

Fig. 2

BIOS-ST (Biobrain Inc., Daejeon, Korea), an 8-channel wireless wearable EEG device.

The device features a sampling rate of 1000 Hz with 24-bit resolution and a bandwidth ranging from DC to 125 Hz, indicating high-performance specifications suitable for both clinical and research applications. In this study, RT and RA were measured under eyes-open conditions.

Data Collection and Analysis

Data for this study were collected before and after the program, and all statistical analyses were conducted using SPSS version 28.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistics were conducted to examine the general characteristics of the participants. The Kolmogorov-Smirnov test was used to verify the normality of the data for determining the use of parametric or non-parametric tests. Baseline homogeneity between the experimental and control groups was examined using independent t-tests. For post-test comparisons, independent t-tests were applied to variables that satisfied baseline homogeneity, whereas analysis of covariance (ANCOVA) was used for variables that did not. ANCOVA is commonly employed to evaluate treatment effects by adjusting for covariates, such as pre-test scores, thereby controlling for initial group differences (Tabachnick and Fidell, 2019). Within-group changes from pre-to posttest were analyzed using paired t-tests following confirmation of normality. Additionally, independent t-tests were conducted to compare the magnitude of change (i.e., pre-post differences) between the two groups.

Results

Normality Testing for Selection of Parametric or Nonparametric Methods

To determine whether parametric or nonparametric statistical methods were appropriate, the normality of the collected data was assessed. All variables satisfied the assumption of normal distribution (Table 2).

Table 2

Normality test for variables

Baseline Homogeneity Test Between Groups

Demographic Characteristics

The baseline homogeneity test for participants’ demographic characteristics showed that, in the experimental group, 5 participants (29%) were aged 20–40 years, 6 (35%) were aged 41–60 years, and 6 (35%) were aged 61–70 years. In the control group, 2 participants (13%) were aged 20–40 years, 11 (69%) were aged 41–60 years, and 3 (19%) were aged 61–70 years (x² = 3.729, p = .155). Regarding gender, the experimental group included 10 females (59%) and 7 males (41%), whereas the control group included 9 females (50%) and 8 males (50%) (x² = 0.259, p = .611). These results indicate no statistically significant differences between the two groups (Table 3).

Table 3

Baseline homogeneity test for participant characteristics

Depression

The baseline homogeneity test for depression revealed a statistically significant difference in BDI scores: the control group receiving conventional psychiatric treatment had a mean score of 16.81, whereas the experimental group— which participated in the CBT-based agro-healing horticultural therapy program, alongside conventional care—had a mean score of 27.65, indicating a lack of homogeneity (p = .045).

Furthermore, CES-D results showed that the experimental group had significantly higher scores in somatic retardation, interpersonal problems, depressed affect, and total depression score, indicating non-homogeneity (p = .013, p = .001, p = 0.01, and p = .004, respectively). However, no significant difference was observed in the positive affect subscale (p = .899), suggesting homogeneity for this domain (Table 4).

Table 4

Baseline homogeneity test for depression

Electroencephalogram (EEG)

Analysis of pre-intervention relative theta power (RT) indicated non-homogeneity at Fp2 and Fz (p = .029, p = .048). For relative alpha power (RA), non-homogeneity was observed at Fp2, T3, O1, Fz, and Pz (p = .029, p = .030, p = .048, p = .034, and p = .030, respectively) (Table 5).

Table 5

Baseline Homogeneity Test for EEG (Unit: μV²)

Within-Group Comparisons of Pre- and Post-Test Means

Depression

For the Beck Depression Inventory (BDI), no statistically significant changes were observed between pre- and post-intervention in either group. In the control group, CES-D scores for interpersonal problems significantly increased from 3.19 (pre-test) to 4.44 (post-test), whereas no significant changes were found in somatic retardation, positive affect, depressed affect, or total depression score.

In the experimental group, CES-D scores showed significant decreases in somatic retardation (14.00 to 9.18), interpersonal problems (6.88 to 3.59), depressed affect (6.71 to 4.06), and total depression score (33.88 to 23.88). No significant change was observed in positive affect (Table 6).

Table 6

Changes in depression scores before and after the intervention in control and experimental groups

Electroencephalogram (EEG)

In the control group, RT significantly decreased at Fp1 following the intervention, whereas in the experimental group, it significantly increased at T3.

RA significantly decreased at Fp2, T3, Fz, and Pz in the control group, while it significantly increased at O1 in the experimental group (Table 7).

Table 7

Changes in pre- and post-test mean EEG values in control and experimental groups

Between-Group Comparisons of Post-Test Means

Depression

Comparison of post-test depression scores between the control group receiving conventional psychiatric treatment and the experimental group—which participated in the CBT-based agro-healing horticultural therapy program, along-side conventional care—revealed no statistically significant differences in BDI or any CES-D subscales (Table 8).

Table 8

Post-test comparison of depression between control and experimental groups

Electroencephalogram (EEG)

Comparison of post-test EEG values between the control and experimental groups showed no statistically significant differences in any RT or RA measures (Table 9).

Table 9

Post-test comparison of EEG between control and experimental groups (unit: μV²)

Discussion

In the control group, which received only conventional psychiatric treatment, scores for interpersonal problems (a sub-dimension of depression) increased significantly following the intervention. In contrast, the experimental group—which participated in the CBT-based agro-healing horticultural therapy program alongside conventional care—demonstrated an overall reduction in depression levels.

Notably, statistically significant improvements were observed in somatic retardation, interpersonal problems, depressed affect, and total depression scores. Moreover, the experimental group showed significantly greater reductions in these depressive domains compared to the control group. These findings suggest that depressive vulnerability extends beyond emotional symptoms and is structurally associated with impairments in social cognition, interpersonal functioning, and relationship maintenance (Kupferberg et al., 2016). Previous studies on horticultural and garden-based interventions have primarily emphasized improvements within experimental groups, often neglecting outcomes in control groups. Additionally, control conditions utilizing “care as usual” (CAU) vary considerably in composition and intensity across studies and institutions, contributing to substantial heterogeneity in reported outcomes (Cuijpers et al., 2021). Therefore, the deterioration in interpersonal functioning observed in the control group in this study should not be interpreted as evidence of the ineffectiveness of conventional treatment. Rather, it may indicate that, in high-risk individuals with depression, interpersonal vulnerabilities can persist unless social functioning is explicitly targeted and reinforced within the intervention framework (Kupferberg et al., 2016). The significant reductions observed in CES-D subscales and total scores in the experimental group are consistent with multicenter studies demonstrating that nature-based therapeutic gardening can significantly improve not only depression and anxiety but also social functioning indicators such as loneliness and overall well-being. These findings are further supported by systematic reviews and meta-analyses that provide robust evidence for the effectiveness of horticultural therapy in reducing depressive symptoms (Zhang et al., 2022). The antidepressant effects observed in this study may be attributable to engagement in the plant life cycle—sowing, cultivation, maintenance, harvesting, and utilization. These activities involve repetitive, goal-directed tasks that facilitate the accumulation of achievement experiences and positive reinforcement. Behavioral activation (BA) is known as a core strategy for alleviating avoidance behaviors and inactivity in depression (Beck et al., 1961; Cuijpers et al., 2013). The horticultural activities implemented in this study may have contributed to the alleviation of depressive symptoms through behavioral activation mechanisms. Furthermore, group-based horticultural activities provide a context that fosters social interaction and emotional support. Collaborative engagement and the sharing of experiences during plant cultivation naturally promote interpersonal connection and bonding among participants. This process can alleviate social isolation and interpersonal withdrawal, which are common features of depression. Indeed, previous research has reported that nature-based therapeutic programs can positively affect the reduction of loneliness and the enhancement of social well-being (Zhang et al., 2022). Accordingly, the significant improvement observed in the interpersonal problems domain in this study may be attributed to these mechanisms of social interaction.

As such, agro-healing horticultural therapy appears to target interpersonal components of depression through multiple pathways, including the promotion of behavioral activation via repetitive, goal-oriented tasks and the facilitation of natural interaction and bonding within group settings.

Furthermore, the program in the present study integrated core CBT strategies—such as cognitive restructuring and problem-solving—into horticultural activities. Through engagement with the processes of plant growth and change, participants may reinterpret their thoughts and behaviors while developing adaptive problem-solving strategies, thereby contributing to the modification of maladaptive cognitive patterns. Particularly within this experiential framework—characterized by repeated cycles of activity, outcome, and interaction—participants accumulate positive experiences, which may help disrupt the vicious cycle of maladaptive cognitions, avoidance, and lack of reinforcement commonly observed in depression. This interpretation is consistent with previous findings indicating that CBT provides additional effects in reducing depressive symptoms beyond conventional treatment alone (Wiles et al., 2013).

However, this study assessed depression using both the Beck Depression Inventory (BDI) and the Center for Epidemiologic Studies Depression Scale (CES-D). While the CES-D demonstrated significant reductions in both subscales and total scores in the experimental group, no statistically significant changes were observed in the BDI. This discrepancy may be explained by differences in the constructs assessed by the two instruments. The BDI is a clinical scale developed primarily to assess the cognitive and severity aspects of depression (Beck et al., 1996), whereas the CES-D is designed to measure the frequency of emotional, somatic, and interpersonal symptoms of depression in the general population (Radloff, 1977). As these instruments capture distinct dimensions of depression (Fountoulakis et al., 2007), intervention effects may be more sensitively detected by one measure over the other.

Meanwhile, this study examined neurophysiological changes associated with the intervention using electroencephalography (EEG) indices. EEG findings can provide supplementary insights into the neural patterns underlying observed symptom changes. In the control group, a decrease in relative alpha power (RA) in the prefrontal and midline regions may reflect reduced neural activity associated with emotional and attentional regulation. The prefrontal cortex has been identified as a key neural substrate involved in rumination and emotional regulation failure (Davidson, 1998), and functional decline in this region may contribute to the persistence of depressive symptoms. In contrast, the experimental group exhibited increased relative theta power (RT) in the temporal region and increased RA in the occipital region, suggesting that sensory stimulation, attention, and cognitive processing were activated during nature-based activities. Interaction with the natural environment can contribute to attention restoration and the recovery of cognitive resources (Kaplan, 1995), and exposure to nature has been reported to improve working memory and attentional performance (Berman et al., 2008). Furthermore, since an increase in alpha waves is associated with a stable state of arousal and internal calm (Klimesch, 1999), the experiences of visual attention and sensory immersion during plant- and nature-based activities may contribute to emotional stabilization and psychological relaxation. Collectively, these findings suggest that agro-healing horticultural therapy exerts beneficial effects on neurophysiological processes related to sensory stimulation, attention, and cognitive processing.

Conclusion

This study is noteworthy in that it integrates core elements of cognitive behavioral therapy (CBT) into the plant life cycle, enabling individuals at high risk for depression to naturally reflect on and regulate their cognitive, emotional, and behavioral patterns throughout the horticultural process. Furthermore, prior evidence indicating that horticultural activities and gardening-based interventions promote mental health and well-being (Soga et al., 2017) reinforces the applicability and empirical basis of this program. By examining both depression scales and EEG-derived brainwave indices, and by comprehensively assessing psychological and neurophysiological changes, this study provides evidence that enhances objectivity and contributes to the development of a more precise evaluation framework for agro-healing. These findings are also meaningful in offering preliminary support for the potential of agrohealing as a non-pharmacological alternative intervention for emotional recovery. However, several limitations should be considered when interpreting the results. The lack of statistically significant post-intervention differences between groups, along with incomplete baseline homogeneity across certain variables, constrains the strength of the conclusions. In particular, baseline imbalances—where the control group exhibited relatively higher levels of depression compared to the experimental group—may have influenced the estimation of intervention effects. Future research should therefore ensure group homogeneity through stratified randomization and larger sample sizes to more rigorously evaluate intervention efficacy. Moreover, it is necessary to clarify the scope and long-term efficacy of agro-healing horticultural therapy interventions through subgroup analysis based on symptom severity and longitudinal follow-up studies.

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No.	Category	Horticultural activity	Title of activity	Psychological integration	Cognitive behavioral intervention
1	Propagation	Sowing vegetables and flowers	I planted the seeds... will they really sprout?	Exploring distorted and negative thoughts, such as “I always kill plants” or “I can’t grow plants,” experienced during sowing.	Recognizing distorted thoughts
2	Propagation	Propagation of herbs and foliage plants	How plants survive being cut.	Reflecting on the resilience of plants that take root after being cut and connecting this to personal experiences of overcoming challenges and setbacks.	Problem-solving
3	Propagation	Transplanting vegetables and flowers	Thanks for Being with Me	Understanding the concept of companion plants and exploring relationships that complement personal shortcomings while fostering mutual growth.	Socialization
4	Management	Pest control and plant care	Overcoming and preventing disease; leaning on others during difficult times.	Identifying active strategies for managing life’s challenges through pest control and recognizing supportive relationships during the process of plant care.	Problem-solving, Socialization
5	Management	Transplanting previously sown plants	Maintaining healthy growth distances (planting distance)	Practicing healthy boundaries in human relationships through appropriate planting distances and learning assertive communication.	Problem-solving, Socialization
6	Management	Fertilizing and harvesting root vegetables (turnips)	Essential nutrients for plant growth.	Identifying the “fertilizer” needed for personal growth and experiencing satisfaction and achievement through harvesting root vegetables.	Problem-solving, Rewards
7	Utilization	Making Floral Tea	The Charm of a Chameleon	Harvest flowers and make floral tea. Through flower tea that changes color according to acidity, recognize yourself as a “chameleon” who has various faces and can put on the right mask at the right time? for example, “Persona! I have many roles and attitudes, and I can adapt flexibly.”	Problem-solving, Rewards Socialization
8	Utilization	Floral arrangement	Celebrating achievements and success with flowers.	Promoting positive self-recognition through floral arrangements, recalling moments of success, and reconstructing distorted thoughts.	Rewards, Cognitive restructuring
10	Utilization	Garden party	Cooking with harvests and decorating with flowers.	Celebrating program completion with peers and expressing gratitude, joy, and satisfaction, fostering positive self-recognition through the culmination experience.	Rewards, Cognitive restructuring

	Item		z	p
	BDI-1		.815	.070^NS

	CES-D		1.267	.081^NS

Brain Wave	RT	Fp1	1.108	.172^NS
		Fp2	0.739	.646^NS
		T3	0.615	.843^NS
		T4	0.739	.646^NS
		O1	0.739	.646^NS
		O2	0.985	.287^NS
		Fz	0.615	.843^NS
		Pz	0.739	.646^NS

	RA	Fp1	0.862	.448^NS
		Fp2	1.108	.172^NS
		T3	0.862	.448^NS
		T4	0.739	.646^NS
		O1	1.108	.172^NS
		O2	0.739	.646^NS
		Fz	0.739	.646^NS
		Pz	0.615	.843^NS

Characteristics	Categories	Cont. (n = 16)	Exp.(n = 17)	x²	p

		n(%)	n(%)
Age	20–40	2(13%)	5(29%)	3.729	.155^NS
	41–60	11(69%)	6(35%)
	61–70	3(19%)	6(35%)

Sex	Male	8(50%)	7(41%)	0.259	.611^NS
Sex	Female	8(50%)	10(59%)	0.259	.611^NS

Items	Subscales	Cont. (n = 16)	Exp. (n = 17)	t	p
	BDI	16.81 ± 12.70^z	27.65 ± 16.71	2.087	.045^*

CES-D	Somatic retardation	8.56 ± 5.63	14.00 ± 6.15	−2.312	.013^*
	Positive affect	6.31 ± 3.66	6.29 ± 3.60	−0.127	.899^NS
	Interpersonal problems	3.19 ± 2.46	6.88 ± 3.20	−3.155	.001^**
	Depressed affect	3.63 ± 3.24	6.71 ± 3.18	−2.393	.010^*
	Total depression score	21.69 ± 10.12	33.88 ± 12.42	−2.524	.004^**

Electrode Sites		EEG Measures

		Cont. (N=16)	Exp.(N=17)	t	p
RT	Fp1	0.540 ± 0.431^z	0.235 ± 0.437	−2.014	.053^NS
	Fp2	1.059 ± 1.289^y	0.334 ±0.210	−2.293	.029^*
	T3	1.243 ± 2.237^z	0.274 ± 0.157	−1.783	.084^NS
	T4	1.089 ± 1.777^z	0.236 ± 0.160	−1.973	.057^NS
	O1	1.206 ± 2.134^z	0.306 ± 0.209	−1.731	.093^NS
	O2	1.286 ± 2.161^z	0.262 ± 0.139	−1.950	.060^NS
	Fz	2.408 ± 4.247^y	0.291 ± 0.199	−2.055	.048^*
	Pz	2.354 ± 5.028^z	0.292 ± 0.153	−1.692	.101^NS

RA	Fp1	2.903 ± 5.664^z	0.146 ± 0.102	−2.008	.053^NS
	Fp2	2.803 ± 4.82^y	0.126 ± 0.061	−2.289	.029^*
	T3	2.991 ± 5.119^y	0.166 ± 0.092	−2.277	.030^*
	T4	0.186 ± 0.109^z	0.167 ± 0.110	−0.488	.629^NS
	O1	0.307 ± 0.235^y	0.175 ± 0.118	−2.058	.048^*
	O2	0.321 ± 0.168^z	0.253 ± 0.131	−1.310	.200^NS
	Fz	2.371 ± 3.922^y	0.266 ± 0.190	−2.212	.034^*
	Pz	3.216 ± 5.266^y	0.316 ± 0.163	−2.272	.030^*

Items	Subscales	z Group	Pre-Test	Post-Test	t	p
BDI		Cont.	16.81 ± 12.70^y	17.56 ± 15.95	−0.176	.863^NS
BDI		Exp.	27.65 ± 16.71	26.77 ± 14.52	0.398	.696^NS

CES-D	Somatic Retardation	Cont.	8.56 ± 5.63	8.25 ± 6.24	0.302	.767^NS
	Somatic Retardation	Exp.	14.00 ± 6.15	9.18 ± 4.28	3.570	.003^*

	Positive Affect	Cont.	6.31 ± 3.66	5.88 ± 3.36	0.659	.520^NS
	Positive Affect	Exp.	6.29 ± 3.60	7.06 ± 2.95	−1.093	.290^NS

	Interpersonal Problems	Cont.	3.19 ± 2.46	4.44 ± 3.37	−1.168	.261^*
	Interpersonal Problems	Exp.	6.88 ± 3.20	3.59 ± 2.90	5.392	.000^***

	Depressed Affect	Cont.	3.63 ± 3.24	3.81 ± 3.54	−0.222	.827^NS
	Depressed Affect	Exp.	6.71 ± 3.18	4.06 ± 2.44	4.283	.001^**

	Total Depression Score	Cont.	21.69 ± 10.12	22.38 ± 12.14	−0.267	.793^NS
	Total Depression Score	Exp.	33.88 ± 12.42	23.88 ± 9.36	4.139	.001^**

EEG Measures	Electrode Sites	z Group	Pre-test	Post-test	t	p
RT	Fp1	Cont.	0.544 ± 0.244	0.384 ± 0.242	2.917	.011^*
	Fp1	Exp.	0.326 ± 0.217	0.399 ± 0.170	−1.345	.179^NS

	Fp2	Cont.	1.059 ± 1.289	0.399 ± 0.256	1.934	.072^NS
	Fp2	Exp.	0.334 ± 0.210	0.400 ± 0.142	−1.303	.192^NS

	T3	Cont.	1.243 ± 2.237	0.304 ± 0.186	1.667	.116^NS
	T3	Exp.	0.274 ± 0.157	0.352 ± 0.118	−1.993	.046^*

	T4	Cont.	1.089 ± 1.777	0.329 ± 0.163	1.684	.113^NS
	T4	Exp.	0.236 ± 0.160	0.329 ± 0.145	−1.759	.079^NS

	O1	Cont.	1.206 ± 2.134	0.266 ± 0.124	1.750	.100^NS
	O1	Exp.	0.306 ± 0.209	0.322 ± 0.143	−0.876	.381^NS

	O2	Cont.	1.286 ± 2.161	0.298 ± 0.179	1.769	.097^NS
	O2	Exp.	0.262 ± 0.139	0.342 ± 0.170	−1.268	.205^NS

	Fz	Cont.	2.408 ± 4.247	0.438 ± 0.207	1.803	.092^NS
	Fz	Exp.	0.291 ± 0.199	0.379 ± 0.140	−1.847	.065^NS

	Pz	Cont.	2.354 ± 5.028	0.353 ± 0.157	1.581	.135^NS
	Pz	Exp.	0.292 ± 0.153	0.348 ± 0.151	−1.208	.227^NS

RA	Fp1	Cont.	2.903 ± 5.664	0.143 ± 0.088	1.965	.068^NS
	Fp1	Exp.	0.146 ± 0.102	0.152 ± 0.061	−1.038	.299^NS

	Fp2	Cont.	2.803 ± 4.826	0.148 ± 0.070	2.210	.043^*
	Fp2	Exp.	0.126 ± 0.061	0.164 ± 0.072	−1.843	.065^NS

	T3	Cont.	2.991 ± 5.119	0.159 ± 0.062	2.205	.043^*
	T3	Exp.	0.166 ± 0.092	0.178 ± 0.068	−1.322	.186^NS

	T4	Cont.	0.186 ± 0.109	0.174 ± 0.078	0.343	.736^NS
	T4	Exp.	0.167 ± 0.110	0.168 ± 0.061	−0.466	.641^NS

	O1	Cont.	0.307 ± 0.235	0.257 ± 0.151	0.774	.451^NS
	O1	Exp.	0.175 ± 0.118	0.206 ± 0.104	−2.132	.033^**

	O2	Cont.	0.321 ± 0.168	0.266 ± 0.122	1.346	.198^NS
	O2	Exp.	0.253 ± 0.131	0.246 ± 0.127	−0.026	.979^NS

	Fz	Cont.	2.371 ± 3.922	0.204 ± 0.081	2.219	.042^*
	Fz	Exp.	0.266 ± 0.190	0.218 ± 0.086	−0.129	.897^NS

	Pz	Cont.	0.322 ±5.266	0.246 ± 0.066	2.261	.039^*
	Pz	Exp.	0.316 ±0.163	0.271 ± 0.103	−1.113	.266^NS

Variables	Subscales	Cont. ( n =16)	Exp. (n = 17)	t	p
BDI		20.96 ± 3.22^y	23.57 ± 3.12	0.320^x	.576^ns

CES-D	Somatic Retardation	9.81 ± 1.12^y	7.71 ± 1.09	1.647^x	.209^ns
	Positive Affect	5.88 ± 3.36^z	7.06 ± 2.95	1.077	0290^NS
	Interpersonal Problems	5.12 ± 0.83^y	2.95 ± 0.80	2.972^x	.095^ns
	Depressed Affect	4.63 ± 0.68^y	3.29 ± 0.66	1.787^x	.191^ns
	Total Depression Score	25.86 ± 2.40^y	20.60 ± 2.32	2.201^x	.148^ns

Electrode Sites	EEG Measures

		Cont. (n = 16)	Exp. (n = 17)	t	p
RT	Fp1	0.384 ± 0.242^z	0.399 ± 0.170	0.199	.843^NS
	Fp2	0.414 ± 0.053^y	0.386 ± 0.052	0.137^X	.714^ns
	T3	0.304 ± 0.186^z	0.352 ± 0.118	0.890	.380^NS
	T4	0.329 ± 0.163^z	0.329 ± 0.145	−0.010	.992^NS
	O1	0.266 ± 0.124^z	0.322 ± 0.143	1.199	.240^NS
	O2	0.298 ± 0.179^z	0.342 ± 0.170	0.730	.471^NS
	Fz	0.469 ± 0.041^y	0.350 ± 0.040	4.076^X	.053^ns
	Pz	0.353 ± 0.157^z	0.348 ± 0.151	−0.090	.929^NS

RA	Fp1	0.143 ± 0.088^z	0.152 ± 0.058	0.359	.722^NS
	Fp2	0.142 ± 0.018^y	0.170 ± 0.018	1.115^X	.300^ns
	T3	0.164 ± 0.017^y	0.174 ± 0.016	0.149^X	.703^ns
	T4	0.174 ± 0.078^z	0.168 ± 0.061	−0.253	.802^NS
	O1	0.246 ± 0.033^y	0.217 ± 0.032	0.389^X	.538^ns
	O2	0.266 ± 0.122^z	0.246 ± 0.127	−0.469	.642^NS
	Fz	0.199 ± 0.022^y	0.222 ± 0.021	0.512^X	.480^ns
	Pz	0.242 ± 0.023^y	0.275 ± 0.022	0.997^X	.326^ns