How to prune buddleia – when to do so and the best methods to use

It is important to know how to prune buddleia to keep it under control, as otherwise this popular and hardy shrub can become a little unruly.

Buddleia, also known as butterfly bush, makes an appearance in many backyards as a fast growing shrub, and its pretty, conical shaped blooms are a magnet for bees and butterflies.

With flowers in colors ranging from pink and white to lavender and deep purple, produced in summer through to fall, buddleias make a lovely addition to flower bed ideas. Follow these tips to keep on top of the pruning, and guarantee your shrub puts on its best floral show.

How to prune buddleia – for beginners

Some varieties of buddleia can become scruffy is left to their own devices and become a tangle of stems, so knowing how to prune buddleia will keep them looking good and encourage new growth and more blooms. This in turn will help to attract butterflies and other foraging pollinators and beneficial insects who flock to the aptly named butterfly bush.

A further good reason for knowing how to prune buddliea is that 'it is considered an invasive species both unofficially and – in some states – officially, by their invasive plant councils,' explains Kathleen Connolly, landscape designer and founder of Speaking of Landscapes. So keeping your shrubs in check will help to curb their vigorous growth.

There are both deciduous varieties of buddleia and evergreen shrubs. Check which variety you are growing in your backyard before getting to work with the pruning shears and secateurs.

'Large buddleia hybrids will benefit from yearly pruning as they are weak-wooded and tend to split with age. Many of the commonly grown buddleia hybrids grow too large for the number of roots they produce. If they are not pruned annually, they will sometimes blow over in the wind,' explains Tony Avent, plantsman and CEO of Plant Delights Nursery in North Carolina.

When should buddleia be pruned?

When buddleia should be pruned, as with most flowering shrubs, depends on two factors: 

• Which zone you live in 
• The variety of buddleia that you have in your backyard

'Generally the best time to prune buddleia begins in early spring, but this will depend on the weather in your area and zone for that year. A good rule of thumb is to use the average last frost date for the zone which is determined by the USDA,' explains Nikki of Perfect Plants nursery in Florida.

Keep an eye on the weather forecasts, particularly if you live in a colder zone, and if frost is predicted in your area, then hold off on pruning until the weather warms up. Some gardeners will be able to commence pruning in March or even late February, whereas others may have to wait until early May.

Most of the Buddleia davidii cultivars flower on new wood, so by pruning in spring you will encourage a bounty of new blossoms. 

'Buddleia should not be cut hard in the fall as the loss of insulating branches and stored sugars may reduce their winter hardiness. Wait for spring to prune your butterfly bushes,' adds Tony Avent.

However, there are a couple of exceptions to this rule as some buddleia cultivars, including B. alternifolia and B. globosa, flower on the previous season's growth, so cutting back in spring would remove the flower buds. Instead, cut out a section of the oldest branches on these varieties in midsummer, after flowering, in the same way as you prune lilac and other shrubs that grow on the previous year's growth.

How do you prune a buddleia bush?

To prune a buddleia bush, first make sure you have the correct tools to hand, which will include pruning shears or saw, secateurs and loppers.

To prune a buddleia that flowers on new growth: 'We generally cut the buddleia bushes back to 1-2 feet tall, but many can be cut to the ground and will recover fine,' explains Tony Avent of Plants Delights Nursery.

Other experts, however, advise against trimming stems down to the ground, as they feel this could cause damage to the plant. 

'If the bush is at the back of a border and you need it to be taller, cut it back to make a frame that is anywhere up to about 4 foot (1.2m) high,' add the experts at seed specialists Thompson & Morgan.

Prune all the stems using loppers, and where possible leave two or three sets of good buds. 

To prune a buddleia that flowers on the previous year's growth: After the shrub has flowered, which will be in mid to late summer, depending on where you live, cut back all the stems that have flowered to healthy buds.

With all buddleia varieties, remove any weak, damaged or old, woody stems, or those that are rubbing against another branch.

Should I deadhead buddleia?

You can deadhead spent blooms on your buddleia shrub throughout the flowering season, and at the same time as you are deadheading roses, or other summer bloomers.

Deadheading faded blooms back to strong shoots will make the bush look tidier and also increase the chances of a second flowering that season.

How do I get more blooms from my butterfly bush?

To get more blooms from your butterfly bush, follow the pruning and deadheading advice to encourage new, healthy growth.

Buddleias are typically hardy in zones 5 to 9, although if you are growing one of the dwarf or compact varieties in a container, these may need winter protection in zones 7 and below.