When should I trim and how drastic?
Anne Arundel County Maryland
By "butterfly shrub," we assume you are referring to the common butterfly bush, Buddleia davidii. These can be pruned in early spring before they start to put out new growth. They can be cut all the way down to about six inches tall.
Please note that these plants are now invasive in Maryland and they are no longer recommended. Here are a couple of links to additional information.