Properly pruning your butterfly bush (Buddleia spp.) keeps this rapidly growing shrub compact and tidy and improves flowering. Strictly speaking, you do not have to cut back your butterfly bush at all. However, it can grow to heights of six to eight feet in just one season and, if you don't make an effort to control growth, you'll end up with a leggy looking shrub with all the blooms at the top. As ornamental shrubs go, butterfly bush is very forgiving and pruning improves the plant's vigor and appearance.
Here's what you need to know to prune your butterfly bush to keep it thriving and looking its best.
When to Prune Your Butterfly Bush
The best time to prune depends on your climate and the size and variety of shrub. Large butterfly bushes at least 4 feet tall benefit from a light cutting back in late autumn to reduce size and improve shape for the next growing season. Autumn pruning in warmer climates has less risk of creating potential for winter damage. However, a conservative trimming in colder climates, done at the right time, can also stabilize a large plant giving it some winter protection.
Light Autumn Pruning
Some butterfly bushes are aggressive reseeders, so much so the cultivars are listed as invasive. Light pruning in autumn, after the bloom period, reduces seed dispersal and also gives the plant better stability for overwintering. Timing is important since pruning stimulates new growth that can be easily damaged by heavy winter weather. In colder growing zones it's better to leave pruning until late winter or early spring, unless your shrub is overgrown.
Hard Pruning in Late Winter or Early Spring
Regardless of climate, hard pruning should be saved for late winter or early spring around the end of February or early March. Dead or diseased branches can be removed any time. Flowers on most cultivars bloom on new wood, so waiting until the first green buds appear at the base of the shrub helps you identify which stems to remove.
Pruning dwarf varieties and non-fertile cultivars should be reserved for late winter or early spring since reseeding is not an overriding issue for sterile plants and cutting back too much in autumn exposes smaller shrubs to winter damage.
Deadheading Butterfly Bushes
Although it isn't necessary, deadheading spent flowers on butterfly bushes throughout summer encourages more flower production later in the season and discourages invasive spread. Use a secateur or hand pruner to cut just below the spent flower at a 45 degree angle.
Tip
Buddleia alternifolia and Buddleia globosa are two cultivars that bloom on old wood. Prune these cultivars after flowering by trimming no more than 1/3 in mid to late summer. Hard pruning reduces flowering for the following season. Make a 45 degree angled cut just above a set of leaves always keeping at least three sets of buds on the branch.
How to Grow and Care for Butterfly Bush
What You'll Need
Equipment / Tools
- Bypass pruner
- Bypass lopper
- Anvil loppers
Materials
- Bag for cuttings, spent blooms, and branches
Instructions
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How to Prune a Butterfly Bush
Whether you decide to prune twice (in autumn and late winter, or just once in late winter/early spring), the methods are basically the same. The notable difference is an autumn pruning is lighter with the goal of managing size and shaping the shrub for the next growing season. A second hard pruning just before or at the start of gardening season is done to stimulate new growth.
Identify Branches For Removal
In autumn, wait until flowering has stopped or slowed to just a few small blooms.
Inspect the butterfly bush for crowding and branches that cross or grow horizontally, straight out from the main stem.
Locate dead and damaged branches.
Remove Dead and Damaged Branches
Use the anvil loppers to prune out dead, damaged and diseased branches at the base.
Head Back Healthy Branches
Use the bypass pruners or loppers to head back healthy branches by no more than one half. You should be cutting new seasonal softwood growth. Use the loppers for thicker branches.
Locate a healthy set of leaves and make the cut just above the leaf set at a 45-degree angle.
Watch for New Growth at the Base of the Shrub
Late February to early March begin watching for new leaves to start budding out near the base of the plant.
Remove Branches in Late Winter or Early Spring
In late winter or early spring, remove dead, diseased, crowded, and crossing branches if you didn't remove them during the autumn.
Use anvil loppers to cut old growth woody branches at the base. Either bypass pruners or bypass loppers are used to remove softer wood depending on branch size.
Remember to make 45-degree angle cuts when working in the center of the bush to remove crowded or crossing branches.
Prune the Entire Plant to One Foot Tall
In later winter or early spring, prune the plant down to about a foot tall. This is to promote new growth and the maximum number of blooms. Use bypass hand pruners or a bypass lopper to cut soft wood and an anvil lopper to prune thicker hardwood branches.
Cut at a 45-degree angle just above the uppermost set of new leaves or existing leaf buds.
Tip
Prune your B. alternifolia or B. globosa in late July or early August following steps 1 through 3. These varieties need only a light pruning to manage shape and size. Over pruning will result in fewer blooms the following year.
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FAQ
How far should you cut back butterfly bushes?
Butterfly bushes should be cut back to a foot tall to promote new growth and the best blooms. You can cut the shrub back to ground level; however, you take the risk of late frost or freeze killing new growth and losing the plant. Hard pruning is done in late February or early March depending on your climate.
Should you deadhead butterfly bushes?
It isn't necessary to deadhead butterfly bushes, but removing spent blooms can encourage more flowers later in the season. For cultivars that reseed deadheading also reduces unwanted spread.
