Mine have been fine at -3 C (27 F). When it got below -4 C (25 F), they received unrecoverable damage. My peruvian (Blue Mac) didn't survive, and I was able to salvage the rest with cuttings.
The one that seems unaffected by cold (and appeared to grow over last winter while under a clear plastic tent) is my Zeller. It's definitely cold-hardy.
Your right I was thinking it was similar to peyote that's another mescaline containing one but it's much hardier. Either way the rain would kill it here before the frost. Not sure we even had one last winter it just rained continuously.
Yes, constant wetness is a sure death. They love getting soaked, but they need to dry out. When dormant, being wet isn't good. I did give mine drips of water last winter, mostly run-off from the tent. The previous winters they looked like they could have used a few light waterings.
