I think your own description contains the answer. These are hardy plants, not intended to be brought in and taken back outside, etc. Way in the way back times, when I worked at a commercial greenhouse/nursery/garden center, we would place all "leftover" perennials in cold frames, make a few attempts to keep rodents out, and call it a day. I think we used hay around the outside for insulation as well, the plants being in pots and therefor exposed to colder temps than if they were actually in the ground.

+oM

Thank you. That is very helpful.

Star trek quote?

Rob

Dammit Jim, I'm a doctor, not a master gardener.