The Pathways and Efficacy of Horticultural Therapy in Promoting College Students' Mental Health: An Explanatory Sequential Mixed-methods Study.

With increasing societal competition, mental health issues among college students have become increasingly prominent, while traditional mental health education often suffers from limited formats and effectiveness. This study investigates the mechanisms and effectiveness of horticultural therapy (HT), a nature-based intervention, in improving college students' mental health using a sequential mixed-methods explanatory design. In the quantitative phase, 112 college students were randomly assigned to an experimental group receiving HT intervention or a control group, with the experimental group participating in eight weekly HT sessions (90 min each) involving activities such as flower arrangement and herbal tea tasting. Intervention effects were assessed using standardized psychological scales and facial expression video analysis. In the qualitative phase, textual data reflecting participants' authentic experiences were collected and analyzed using grounded theory with NVivo 12. Results showed that, compared with the control group, the experimental group demonstrated significantly higher post-intervention scores in meaning in life (p = 0.017), overall affect index (p = 0.044), and life satisfaction (p = 0.046). Within the experimental group, post-intervention levels of meaning in life (p = 0.02), affect balance (p = 0.007), and positive affect (p = 0.019) were significantly higher than pre-intervention values. Facial expression analysis revealed notable differences in the distribution of seven expressions between groups, with positive expressions increasing over time, particularly during flower arranging and tea tasting activities. Qualitative analysis further identified a four-layer pathway model (Environment → Cognition → Emotion → Behavior), explaining 36%, 32%, 16%, and 15% of the variance, respectively. Overall, horticultural therapy effectively enhances college students' life satisfaction, sense of life meaning, and affect balance, thereby improving mental health through a multi-layered psychological pathway.