I receive emails from all over the world asking me about Passionflower care, -
Although i'm not an expert about growing in the different climates of the USA, or Norway, or Thailand or Spain, - here are the basic things you need to know about Passion flowers in the winter.
Passiflora Caerula which is the common hardy variety in the UK, has a purple and white flower with yellow stamen.
It is an evergreen in very sheltered conditions, but will loose its leaves by the time the temperature falls below zero on a more than occasional basis. This variety i've seen survive winters of -5-7degrees C, but the older and more established the plant the better its chances of surviving. Most text books say that it is moderatly hardy down to -3 degrees C.
As Caerulea can be quite a thug see previous passiflora post for details being cut back to ground level by frost occasionally can be quite an advantage.
If your Passiflora Caerula is in a pot, - this is probably restricting growth quite dramatically so the plant may be acting in a juvinile form, - this means that it won't survive quite as low temperatures, - i'd suggest a good lagging around the pot, and a top dressing of mulch to keep it warm, - also ensure good drainage.
If you have a varieity other than Caerula, particularly if it is a red coloured flower, then it is less likely to be hardy, and it is very likely to need winter protection and a frost free greenhouse.