How many times do you get frost? When is the usual date for first frost? If you can put them in a greenhouse, do so before first frost. If no greenhouse, pthem in a sun room. Be sure they are in a soil which will retain some moisture or be prepared to water often. Bougainvilla may drop its leaves but will sprout back. If you have very few cold days, you can put them in a garage and drag them inside and outside as weather permits.

I have heard people doing a "hard prune". What exactly does that mean?