Ok, -14 will definitely kill them. lol
I thought it was much milder on average though.
You can still benefit if you leave it outside where it is cold but make sure you bring them in when the temperature is expected to go below 0 C.
Cold winter really bring out the best flowering out of these plants.
If you have unheated greenhouse, it should be good enough even when it is freezing outside, isn't??
I used to winter all my nobiles at my friends who had unheated balcony. Those were the days when my nobiles bloomed in full glory!
You don't need to fertilize until after flowers fade or when you see new shoots.
Now this is rather grey because when these are grown in ideal conditions (cold winter and gradual warming in the spring) new shoots usually do not appear until flowers are all open. When they are grown too warm, new shoots will start to grow early on. Fertilizing is recommended as soon as the new shoots develop, but developing flower buds do not need fertilizing. The canes have all they need already.
Cold temperature is an important cue for the flowers to develop.