Answer: This plant may be marginally hardy for you, depending on the exposure where it is planted. A windy location would be the coldest.
Butterfly bushes are normally pruned in the spring. This allows the branches to protect the lower part of the plant a little bit during the winter. In a cold winter, they may die back to the ground and then regrow from the roots, in a milder season they may only need shaping. In any case, in late spring remove any dead wood and then be patient for signs of new growth.
This plant loves heat and sun, so it takes a while for it to awaken fully in the spring. It blooms on new growth of the season so you should still see a nice display. Next fall, apply a healthy layer of mulch over the root system to help insulate it.
Good luck with your butterfly bush!
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