Even the southern species are hardier than they are given credit for. A few years ago I had all my Sarracenia in a gigantic tub that was frozen solid for 3 days straight and I didn't lose a single plant. I think the duration of cold is more lethal than actual temperatures. Even at this time of year, I don't think 25 degrees is going to hurt them, if it's just an overnite occurrence. It's certainly not going to kill them.