Last updated on January 25th, 2022
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There is no mistaking the fragrant, spiked flowers of Buddleia davidii shrubs. Often available in an array of colours, from the vibrant royal red flowers of ‘Royal Red’ to the white flowers of Buddleia ‘Marbled White’, they are highly attractive to a variety of beautiful butterflies, our much-loved bees and other beneficial insects that pollinate our plants.
Most Buddleia shrubs originate from the rocky mountains of China and as such, they are very adaptable to living in most conditions which is why you see them growing in the cracks of old bridges, alongside railway tracks and around abandoned concrete buildings.
Most Buddleias, which include mainly the davidii hybrid cultivars and B. lindleyana cultivars can be pruned back hard. These types of Buddleias flower in the summer on the ends of the new growth and are best pruned in spring when they have started to put on some good growth, which is usually around March or April.
How to prune Buddleia
They are very hardy and it is actually very difficult to cut them back too hard and cause them any harm, so don’t be afraid to prune back aggressively. Ideally, you want to prune back hard to around 1-2ft (30-60cm) from the ground leaving a good framework with lots of new shoots on. Try to avoid pruning too far down into the older wood with no growth as it may struggle to get going again quickly. That being said, they nearly always come back no matter how hard you prune them so don’t worry too much.
Feeding and mulching
After pruning in spring, mulch and feed to encourage healthy new growth because Buddleias store some of their nutrients in the young stems and these will be removed in spring when pruned. Ideally, you want to feed them with a high in potash (potassium) feed such as Vitax Q4 or a good quality rose feed that helps to promote flowers. Usually sold as a granular feed they are easy to apply, simply sprinkle around the base of the plant and then raking it in lightly should do the trick. Read the instructions on fertilisers and feeds carefully for exact application amounts. Feeding when in flower can also help. A good cheap feed you can use, believe it or not, is Tomato feed as it is high in potash and is designed to promote more flowers.
Prune later to encourage butterflies into the garden
Buddleia is also commonly known as the ‘butterfly bush’. This is because they are highly attractive to butterflies and they can often be seen smothered by them. You can help the butterflies by pruning your Buddleia slightly later, around late April to early May which will make the main flush of flowers appear slightly later in summer around August, just as the butterflies make an appearance and need our help.
Try to avoid pruning Buddleia too early or when a hard frost is expected because a hard frost can damage the branches where they have been pruned.
Did you know that some types of Buddleia should not be pruned back hard?
The earlier flowering cultivars, which include B.globosa, B.colvilei and B.alternifolia flower on the previous year’s growth so should not be pruned in spring as you will be cutting off the growth that produces next year’s flowers.
These later flowering varieties need to be dead-headed (removal of the faded flowers) and given a general tidy to removing any weak or damaged branches after flowering but do not prune hard.
How to prune correctly
When you prune back the branches, always cut at an angle sloping downwards so the rain can run down the cut and not settle on it as this can increase the chances of diseases getting into the ends of branches. Watch out for bacterial canker, bracket fungi, verticillium wilt and coral spot.
How to increase the flowering time
Buddleias are prolific flowerers and if you remove flowers as they fade they will produce new flushes of flowers and can flower 2 to 3 times in one season. Do not allow the faded flowers to go to seed as the plant will then focus all of its energy on seeding and not flowering.
How you can help small birds during the winter
Finally, leave the last flush of flowers on in late summer as this attracts small birds into the garden and the seeds provide food for them over winter.