I live in Santa Rosa CA ('m not sure of which zone that is-- there are several differing zones around) I've been growing brugmansias for about 15 years in large containers like half wine barrels which obviously I can't easily take inside when we have frosts, or nights down to 23 degrees for a week! I do NOT cut off the branches when it is really cold-- sometimes I cover the container or at least put a thick mulch all around the roots, etc. They look terrible, but leaving the stalks and dead leaves on the plants helps to protect them. The plants usually die down to the ground-- even the ones that I have grown in the ground-- but come back from the roots. It all depends on how cold, for how long. last year e had a very cold, dry winter. It took all my brugs a much longer time to come into bloom this summer, and some of them never did. The pink ones seem to be the heaviest bloomers and the most willng to bloom nomatter what. I have a couple of yellow ones that are just now forming buds. (this is early Nov.) Brugs, like most solonaceous plants, are quite easy to start from cuttings. Whenever I prune them in the spring, I always take a few cuttings and put them in water until roots form, and then pot them up to give as gifts, or just to have more...
they are heavy feeders also, and love a lot of water so they're not the most practical of plants but the scent is certainly addicting!