Answer: Several plants go by the common name Butterfly Bush, but I'm going to assume that you are referring to Buddleia davidii, which blooms on new growth. Therefore, stems should be pruned back in late winter/early spring to encourage large, lush flower spikes. You can let it grow into a shrub form, (which could eventually be about 12'x15') but your flower "show" won't be as spectacular. It's also a good idea to protect the root system during the winter by mounding dirt and mulch over it. Buddleia can sometimes be slow to show new growth, especially if the spring weather has been cool and overcast. I'd give the plant a few more weeks to grow.
Best wishes with your butterfly bush.
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