Yes, butterfly bushes should be pruned back in the spring, sometime around when the first buds are forming at the base of the plant - late March to early April, depending on how the temps are. Mine is around 6 feet or so, and I haven't had a problem with the branches breaking off or anything in the snow - looks really pretty in winter !

My older buddleia grow to seven and eight feet tall. They have never been impacted by snow on the branches; the branches are not stiff enough to break. Enjoy the Spring pruning; it's exciting because the flowers follow by early July. Enjoy.

Thanks - I'll enjoy the height outside the living room window for the winter and cut back in the spring.