My friend's a collector of passifloras and he has been successful overwintering this p. incaranata to around -25Celsius (-13F?). He thinks it needs a bit of dryness during the winter because it has only survived when he planted it next to a wall. This is Zone 5 near montreal, quebec. It makes little rhizomes that you can easily divide to make insane amounts of plants. he once dug up all the rhizomes of a plant he had planted at a church only to find several plants growing from the ground the year after! A couple of years later they cover an entire wall of the church a you can get lots of fruit at the end of the season which are of course edible. he's looking to make hybrids with other hardy passifloras like caerulea to get bigger flowers...