Poinsettias are tropical so you would have to wait until there is no more danger of frost. The "flowers" are actually colored leaves which are called "bracts". They often remain on the plant for quite a while. Once you plant them outdoors in a container, the plants will grow a lot of new green growth. But poinsettias are "short day" plants, which means that if you want to get them to bloom again, they'll need several weeks when they receive light for 8 hours a day or less, so come October you will have to put them in a dark place (closet?) or cover with a light-proof cardboard carton or something similar for 16 hours a day (say from 4PM until 8AM the next morning. And during that 16 hours of dark time, even a little exposure to light could inhibit the flowering process. It can be done, but they're not expensive so most people just buy a new one the next year. But they do grow some really nice green foliage in summer outdoors, maybe as a filler for your container.

Thanks Bill. I've never had a pointsetta that looked nice beyond January before. I'm not trying to "save" my pointsetta for next Christmas - it's more that I like interesting colors and textures in pots on my patio each summer. So if the plants are still looking healthy in May, it won't hurt to pot them up and put them on the patio. If worse comes to worse, I can just dump them in the brush pile.