Answer: These shrubs bloom on new growth, so the time to prune is in the early spring. Cut it back quite hard to stimulate new growth. Trim to maintain the basic framework and shape of the rounded top. As it grows in, you can pinch out the tips or very lightly shear it once or twice during the first month. This will encourage branching. After that, do not prune it. You may however deadhead it (trim off faded blooms) to encourage heavier blooming throughout the season.
Also, if it is in a container, you should bring it into a sheltered but cold place for the coldest months of January, February and probably March. An unheated garage would do; water only enough to keep the soil from going bone dry while it is indoors. Take it back out in early spring as the weather begins to moderate. Good luck with your butterfly bush!
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