I only speak from my experience....I live in Chicago USA and our summers are brutally hot( 80 Degree Fahrenheit/102 degree Fahrenheit) and our winters are also brutal(30 Degree Fahrenheit/ -20 Degree Fahrenheit ) I keep all of me Sarras and Dioneas outdoors all year round with no protection( no green house). In the fall, the potted plants are bagged up in large black garbage bags(making sure soil is moist) then placed around the in ground bog tubs then buried in 10 -15 inch of straw, then next spring(March 17 St Patrick's Day) is when I remove all straws then I take them out of bags to expose them to the spring sun to get a jump-kick of energy to get the growth started and I tell you, both my Sarras and Dioneas come back healthier and more vigorous because of that rest. You mentioned you have a cold frame, I would say that frame would suffice as a wintering place for your VFT's (like the straw and bag that I use) and yes they do need that cold rest so they'd come back stronger and bigger next growing season...Good Luck