Answer: If you need to trim your butterfly bush back before transplanting, I'd recommend waiting until spring. Pruning encourages new growth which won't have time to harden off before winter weather arrives. As a result, it will die back and will need to be pruned again in the spring. While that might seem problematic, it does sap the plant's energy - and that extra bit of energy might be needed for new growth in the spring. If you can move your butterfly bush without trimming first, you can move it in the fall. Otherwise, I'd wait to trim and move it in the spring.
Best wishes with your landscape!
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