Stevia Dying Off

Last year I bought some stevia plants from you. Unfortunatly they all died off during the winter. I would like to order more plants, but not if they too are going to die. My question is, do stevia plants just die back in winter, and come back in spring? Or do they need to be in greenhouses. I live in central California. We do sometimes get a soft freeze, but nothing that lasts very long or is all that cold. I hope you can help with these questions, and I can try again.

Stevia cannot take any frost at all, You will have to take it in during the winter and keep it warm. If you don't want it to die down in the winter you will also have to lengthen its days to summer day length.