The effect of horticultural therapy on older adults in pension institutions: a systematic review

•Older adults in pension institutions are in a special closed isolation phase and are prone to a variety of mental health problems, especially during the COVID-19 pandemic.•HT can improve the physical, physiological, psychological, and quality of life functions of older adults in pension institutions and alleviate their somatic aging.•HT can provide both healthy nutritional support and improved physical activity, mental health, and stress management for older adults, and is worth promoting in long-term institutions, especially in times of the COVID-19 pandemic.