I don't see how the cold could be killing them in Zone 10. Are you watering them a lot? Most passionvines really like good drainage, no soggy roots. Or maybe you're letting them get too dry? They're not swamp plants, but not desert plants either.

I'm really surprised that someone in your part of California would have trouble overwintering any passionvine, even the tropical ones.

Sherry

I don`t either, we do get frost here I am close to the mountains,maybe cover in the winter possibly....................... thank you for answering me.