The kill temperature for Fava Beans ranges from about -4c to -10c depending on the variety. Furthermore the temperature needs to be sustained; that is 2 minutes at -4c will not kill the fava bean plant; neither will an hour (most likely).... but 48 hours of temperatures consistently below -4c might. When the cold temperature is sustained the cells of the plant explode (freeze); it is the "water transportation system" that gets damaged and the plant can't continue. If you are expecting colder than average temperatures (or colder than you expect your fava beans to be able to handle) - you can cover them with plastic (clear if your keeping it on - anything if you are just putting it on top of them overnight). Tent style is best, but umbrella style (no sides) is also helpful. The most difficult time for the plants is usually around 4am when the "dew" settles, if during cold temp days you can get the plants covered overnight not only will the soil help keep them warm, you are keeping that cold morning sweat off them which can really do considerable damage if temps are cold. Also, high winds work like the morning dew; transporting the cold temperatures into the plant more readily.

- Celeste Archer