Answer: Butterfly Bush, also known as Buddleia davidii, blooms on new growth. Therefore, stems should be pruned back in 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. FYI, I always prune back my Butterfly Bush on St. Patrick's Day to about 6"-10". Whether planted in the ground or in a container, your butterfly bushes should winter over outdoors without problem. If you'd like to mulch over the roots of your butterfly bushes, you'll help them from heaving out of the ground during alternating freezes and thaws. The most common reason for plants failing to survive the winter is poorly draining soils which suffocate the roots.
Hope you have better luck with your butterfly bush this winter!
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