Currently I have a few H. montanus which I raised from seed and have been growing permanently outside for a few years. We had a 'once in 30 year winter' last year and temps here fell to -4C on several occasions with daytimes staying below 3C for 5 consecutive days. They survived that easily, but no flowers this year. This winter has started as though it is going to be a second 'once in 30 yrs ...' (!!!) and the leaves are still alive, but a rather dark, 'greasy' green. Between 1999 and 2008 I had H. albiflos growing permanently outside and during that period, temps only rarely fell to around -2C for very short periods in winter. It didn't receive any special treatment and during very wet winters, the roots almost completely rotted away. By early May the plants would be rooting strongly again and the growth flowered regularly in June each year. Maybe if I'd added plenty of grit when planting, albiflos would have done even better, but it's not exactly the most treasured or rarest of plants and it was originally an offset that was just pushed into the ground.