Butterfly bushes (Buddleia) are deciduous shrubs that bloom on new wood. They are hardy in U.S. Department of Agriculture Plant Hardiness Zones 5 through 9. In harsh winters, they may die back entirely to the ground in zones 5 and 6, but will send up new shoots from the rootstock in spring. Prune them for shape in the spring and then for continued flower production throughout the season. With care, they can be transplanted any time during the growing season, but spring or fall is best.
Cut out any stems that are broken or have died over the winter. Make the cut just above a leaf or stem node.
Prune out any stems that cross or rub against other stems. Also cut out any spindly, weak or diseased growth.
Cut remaining stems back to 12 to 18 inches above ground level. Cut the stems into a rounded form to give the shrub a nice shape as it puts out new growth. Cut to ground level if you want a more compact shrub.
Remove spent blossoms by cutting the end of the stem back to a leaf node. New flowers will form on the ends of the branches that emerge from the leaf node.
Prune branches to a leaf or stem node farther back on the stem if the shrub gets too big. The shrub will recover quickly and flowering will not be affected.
Prune the shrub down to 12 to 18 inches. Water well to make digging easier, but do not remove the bush until the new planting hole is ready.
Choose a new planting site in full sun. Good drainage is a must. Dig a planting hole 12 inches deep by 18 to 24 inches wide.
Enrich the soil in the new planting hole by mixing organic matter with the soil. Compost or well-rotted manure work well.
Dig up the pruned butterfly bush, being careful to take as many roots as possible. Cut straight down around the sides of the rootball, then cut across the bottom.
Place the butterfly bush into the prepared planting hole, making sure the shrub is at the same level as before. Fill in around the roots with the amended soil. Water well to settle the soil and remove any air pockets.
Whenever pruning any shrub, it's best to dip the shears into an antiseptic between cuts to prevent spreading disease. You can use a solution of one part household bleach to 10 parts water. A sharpened spade or shovel makes clean cuts on the roots, helping prevent disease.