Mung bean seeds require four to five days of 65 to 70 degree Fahrenheit temperature to form bean sprouts. Planted outside at a depth of 1.5 inches, mung bean seeds prefer a soil temperature of 60 F or warmer. The maximum soil growing temperature for the warm season annual is about 95 F.
Mung bean seeds sprout at a 50 F temperature, but at a low temperature, the seeds crack and microbes enter. This reduces germination percentage, especially in light-colored seeds. At temperatures lower than 50 F, germination is usually poor.
Depending on the variety, mung bean seeds are mottled green, yellow or brown. Seed companies or gourmet food stores sell mung bean seeds. Mung bean plants require 90 to 120 frost-free days to mature.