Soil temperature, rather than air, determines whether bean seeds will emerge from dormancy.
Fluctuating day and night air temperatures, particularly in northern climates in the spring, affect soil temperature. Bean seeds need soil to stay consistently warm for an extended period for germination to occur.
The optimal temperature for most bean seed germination is from 75 to 80 degrees F; for lima beans, the optimal temperature is 85 degrees. The minimum is 60 degrees for limas and other beans. The maximum temperature is 85 for limas and 95 for other beans. Germination takes between seven and 10 days.
Sowing beans when soil is too cold may result in seeds rotting.
The right temperature is not the only thing bean seeds need to germinate and grow. Other factors, such as water and soil that offers enough nutrients, are also necessary.