Activities related to plants, such as wheat field tourism, agricultural variety shows, and farm-based educational programs, have gained popularity among undergraduate students. Some graduates choose to become “new farmers” and contribute to rural revitalization after graduation. Horticultural therapy is a non-pharmacological therapeutic approach that has developed independently from the concept of horticulture. Objective: To evaluate the effectiveness of horticultural therapy in alleviating stress among undergraduate students. Methods: A total of 66 undergraduate students were recruited voluntarily and randomly assigned to an experimental group and a control group. The experimental group received a 5-week horticultural therapy intervention, consisting of one session per week, each lasting 1 to 1.5 hours. The control group did not receive any intervention. The Perceived Stress Scale (PSS) was used for pre-test and post-test assessments. Results: Prior to the intervention, there were no significant differences in stress levels between the experimental and control groups. After the intervention, the experimental group’s stress levels were significantly lower than those of the control group. Two weeks after the intervention, the experimental group continued to show significantly lower stress levels compared to the control group. Conclusion: Horticultural therapy can effectively reduce psychological stress among undergraduate students.