I have also found that it can take quite a lot of cold.
Here in the UK we occasionally get a few days down to 25F at night, hovering at freezing to 32F during the day, and my plants have survived this with no additional heat as long as the soil is not too wet and the light levels are adequate. Even if the top growth is damaged by frost and lost, new growth from any remaining roots does occur when the plants start growing in Spring.