Horticulture can reduce negative symptoms associated with chronic mental illness. This study analyzed and described the process of applying a horticultural training model in a psychiatric center. A total of 107 participants with chronic mental illness were included. Participants had an average age of 45.4 years; 64.5% were men, and 89.7% were diagnosed with schizophrenia. Data were collected over 9 months from a data collection system called the Quality Control System of Occupational Therapy. Of the 12 horticultural training items, sweeping, watering, and weeding demonstrated the highest execution rate (57.49%, 35.31%, and 32.32%, respectively). The average sustained time undertaking horticultural training was 1.61 hours per day, and the average number of executed items was 1.58 per day. On the basis of these observations, the establishment of horticultural training is recommended for chronic psychiatric patients. Activities such as sweeping, watering, and pulling grass can serve as basic training, before gradually moving to more advanced techniques such as pruning, cutting, and transplanting.