Hello,
I have all of the Flemming hybrids mentionned and they survive our Canadian winters just fine with a bit of extra care. In the autumn I mound dirt, compost, leaves, whatever is on hand, to a height of 12 inches up the main stem and out to the drip line of the plant. This gives it additional insulation for the winters. Do not worry about cutting the stems, I leave them in place so I will be able to find the plant next year. The following late spring ( June ish here) I slowly remove the mulch day by day so as to not give it too great a shock. The new shoots from the roots usually occur late in June, but by August the plants are in full swing. I hope this helps, don't hesitate to ask if you have other questions.

Wow, late June? that's a long dormancy. I just threw a handful of mulch on each plant. This fall I am going to do better than that. Thank you for the advice.I really love them and hate to lose any.