The mental health needs of older adults are a growing concern, and as technology advances, integrating health information with technology can improve healthcare quality and dissemination efficiency. Integrating health information with technology holds promise for enhancing healthcare quality and dissemination efficiency in practical applications, thereby equipping more individuals with accurate health maintenance knowledge. Particularly notable is the increasing trend in internet usage among modern seniors, which contributes to achieving United Nations Sustainable Development Goals. Horticultural therapy has been widely acknowledged for its positive impact on human well-being in various settings. However, its integration with information technology remains relatively unexplored. Additionally, studies on its effectiveness in relieving stress have demonstrated inconsistent effects on heart rate variability. Therefore, this study aims to examine how technology-assisted horticultural therapy influences stress, depression, and happiness among older adult residents in long-term care facilities, with a specific focus on regulating the autonomic nervous system. The study will employ both subjective questionnaire surveys and objective measurements of heart rate. This study proposes a cluster randomized controlled trial. Using G-Power 3.1, a minimum sample size of 76 participants is calculated, accounting for an estimated 20% attrition rate. To ensure equitable distribution between intervention and control groups, each group will consist of at least 38 participants. The intervention involves technology-assisted horticultural therapy sessions conducted once a week, lasting 120 minutes per session, over a total period of 8 weeks. The research will employ several tools: (1) a basic demographic questionnaire, (2) the Mini-Mental State Examination (MMSE), (3) the 'Taiwan Scientific' Noninvasive Blood Pressure Meter (TS 0411), (4) the Perceived Stress Scale (PSS), (5) the Geriatric Depression Scale (GDS-15), and (6) the 5-item World Health Organization Well-Being Index (WHO-5). Data collection will span pre-, mid-, and post-intervention periods over 8 weeks for both experimental and control groups. The Efficacy of Horticultural Therapy Evaluation Form (EHTE) will also be used to conduct pre-test and post-test evaluations on the experimental group. Data will be analyzed using SPSS 27.0. Descriptive statistics will be applied to the demographic questionnaire data, while generalized estimating equations (GEE) will analyze pre-, mid-, and post-test questionnaire responses and objective measurements. Empirical evidence from this study will elucidate the impact of technology-assisted horticultural therapy on heart rate variability, stress, depression, and happiness among older adult residents in long-term care facilities. These findings will serve as a basis for developing health pro-motion programs aimed at enhancing the physical and mental well-being of aging populations.