Why can scarlet runner beans grow on Mount Meru but not set pods in low-elevation Hong Kong?

The primary reason scarlet runner beans fail to set pods in low-elevation Hong Kong, despite thriving on the high slopes of Mount Meru, is the influence of elevation on climate.

While the scarlet runner bean is a temperate plant, elevation serves as a critical determining factor for its cultivation in tropical and subtropical regions. High-altitude environments provide the cooler conditions necessary for the plant to flower and develop pods successfully. In contrast, low-elevation areas like Hong Kong—situated near the Tropic of Cancer—lack the specific climatic requirements needed for this process, preventing the plant from setting pods even if it can grow in those regions.1