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I'm growing Cypripidium reginae in a pot here in the middle of England. Yet to find out how it comes out of dormancy after being outside for the winter.
However I was told by someone at a show recently that another seller they had been speaking too had had it go down to -19C in Scotland and all the cyps in pots outside came back up the next year, all be it a little late.
The cyps need a certain amount of cold (below freezing) I'm told. Someone here on OB was growing them in the garden in Canada and aparently they do well despite really low temps, however they need to be kept dry when it's really really cold.