Answer: I wouldn't prune it at this point - you don't want to further stress your butterfly bush. Instead, just water it deeply once each week (twice in really hot weather) and give it some time to adjust to its new home. As soon as the roots become established it will perk up. When you see new growth, you'll know it is firmly established and you can prune out anything that's obviously dead. Deep watering is the key. Try mounding soil up in a ring around the base of the plant to use as a water basin or water well. Fill the basin with water, allow it to drain and then fill it a second time. This will concentrate the moisture directly over the root mass and allow it to trickle down and wet the entire root mass. Do this once (or twice) a week. Your plant should perk up soon. What's nice about butterfly bushes is that they grow quickly and even if pruned way down, they will respond with lots of new growth during the spring and summer months.
Best wishes with your landscape!
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