Gerry!
I live in south central Wisconsin, and my first year with daylilies, because of a variety of reasons, I still had some in pots. Realize that the pots were the large plastic kitty litter bins that I had drilled holes in and had gravel on the bottom for drainage. I put them in a protected corner next to my house, mulched them well - and lost every single one of them in the spring.
I was told that I should have laid the pots on their sides - that they died of rot in the icky spring we had. Since then I have never overwintered outside.
Others here do overwinter in pots up here in the north. As for a cold greenhouse, I can't answer that, but I am sure there are others here who can.
Again, welcome ~Jan
