Contemporary society faces an unprecedented wave of mental health crises and environmental degradation driven by rapid urbanization and technological integration. Natural interventions, specifically forest therapy and garden therapy, have emerged as vital, low-cost, and side-effect-free components of holistic preventive medicine. This paper clarifies the fundamental distinctions between these two healing models under the Plant-Based Adjunctive Therapies (PLAT) framework, categorizing forest therapy as passive, immersive Plant Perceptive Therapy (PPET) and garden therapy as active, reciprocal Horticultural Therapy (HT). Grounded in Attention Restoration Theory (ART) and Stress Recovery Theory (SRT), the therapeutic mechanisms are analyzed across environmental, experiential, and institutional dimensions. Empirical evidence demonstrates that forest therapy significantly enhances immune functions, such as natural killer (NK) cell activity via phytoncides, and regulates cardiovascular health. Conversely, garden therapy excels in accessibility and targeted rehabilitation, employing universal design features like circular paths and elevated planting beds to accommodate specific populations, including individuals with dementia, autism spectrum disorder, and visual impairments. Globally, natural healing is increasingly integrated into formal public health sectors, exemplified by Taiwan’s professional green prescription certification, the United Kingdom’s social prescribing scheme, and Europe’s care farming initiatives. Despite their documented physiological and psychological benefits, transitioning these therapies into mainstream medicine requires overcoming challenges related to clinical standardization, dose-response quantification, and health insurance policy support. Ultimately, forest and garden therapies form a complementary matrix of perception and nurturing, mending the severed connection between humanity and nature while establishing a new paradigm for inclusive, sustainable, and holistic healthcare infrastructure.