Answer: Butterfly bushes are normally left unpruned until spring. They atart into growth rather late in the season, especially if they have been pruned hard, so be patient. We had a mild winter so I would expect them to come back, but fall pruning can be a bit of a shock for them.
Butterfly bushes can be pruned several ways. One
method is to prune it off close to the ground to renew it if it
has become overgrown and gangly, or if the winter has
damaged it (or even killed it back tot he ground) severely.
This will stimulate new growth from the roots and also help
to control overall size. In warmer areas, the shrubs can
become very large and this pruning method occasionally
makes very good sense.
Some gardeners prefer to prune
away any winter killed branches and then prune lightly just a bit
for overall shape and to encourage branching so the plant
grows denser. This will result in more flowers, because the
blooms form at the branch tips.
Other gardeners will prune it back by about half as a compromise to controlling size and keeping it bushy. It's really a matter of
personal preference. If you are happy with the shape and blooming performance, you
don't really have to prune it at all.
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