Butterfly Bush are best trimmed in early spring, around March or so. You can cut them back as far as you'd like, though we suggest leaving at least 12 to 18 inches of stem above the ground to facilitate regrowth. Cutting them back now may risk damage from winter cold or freeze-thaw cycles. Dead branches can be removed any time of year, since the tissues you'd be cutting off are already dead and therefore not vulnerable to seasonal changes. If it's easier to identify dead branches now, you can trim those off in the next week or so, but otherwise their removal will probably be taken care of when you drastically cut the plant back next spring.

If the variety you're growing is not sterile (few are, though it remains to be seen how truly sterile they stay), cut off any spent flowers that might be forming seeds. Butterfly Bush is an invasive species in Maryland, and any fertile seeds could help the plant spread into natural areas and out-compete native plants. If you're amenable, we recommend that non-sterile Butterfly Bushes be replaced with other species. Even if your shrub is a sterile variety, it won't hurt to remove any spent flower clusters now, just in case they have a small number of fertile seeds among them that wind or wildlife will move around.

Miri