Pruning buddleia: when & how?


For me plants are some of the most exciting living beings, even though they live in slow motion. They have fascinating abilities and just so much potential! That's why I studied organic farming. However, since plants are rather thin on the ground in my city, I often spend time hiking in the nearby mountains at the weekend. In the future I would love to run a farm myself.

Favourite fruit: strawberries and gooseberries
Favourite vegetable: courgettes

Butterfly bush, also called buddleia or buddleja, is very popular in many gardens. Indeed, these colourful flowering shrubs attract butterflies with their nectar. We explain all about pruning buddleia.

Butterflies on butterfly bush flowers
Butterfly bush flowers are a magnet for numerous butterflies and bumblebees [Photo: Lonspera/]

Countless hearts of amateur gardeners have already been conquered by the once exotic butterfly bush (Buddleja davidii). Its success is due to the abundance of flowers that attract butterflies in droves. In order for the bush to bloom richly every year anew, pruning is necessary from time to time. Although not strictly necessary, it can spur lazy specimens on to new efforts. In addition, buddleia bushes have a very lush growth. Therefore, to keep them smaller, regular pruning becomes indispensable. Rejuvenation pruning works wonders, especially for balding buddleia.

As buddleia bushes have a strong need to spread it is also quite sensible to remove wilted plants promptly.

When should buddleia be cut back?

In late winter or early spring: rejuvenation pruning

Prune your butterfly bush in late winter or in early spring. At this point in time, the summer lilac is not in sap and there are no birds or other creatures nesting in its branches. The best time for pruning is February on a frost-free day. In late winter, you can also give your buddleia a drastic pruning to rejuvenate it.

In autumn: trim if necessary

In autumn after flowering, you can also prune your butterfly bushes, you should, however, not proceed so radically as in the winter pruning. So, at most you should undertake only small adjustments, for example, if the shrub needs to be trimmed back a little.

In late summer and autumn: remove withered flowers

It is important to remove withered flowers in late summer and autumn. The flowering period of the plant is between July and September. Butterfly bushes produce huge amounts of seed – if you neglect to cut away the withered flowers, you will soon have summer lilac everywhere.

Buddleia inflorescence full of seeds
Prune buddleia inflorescences before the seeds form [Photo: Ian Grainger/].

Instructions for pruning buddleia

Butterfly bushes are very fast growing and very tolerant to pruning. So, when pruning you cannot go far wrong. Even if you want to be more radical once in a while, you do not have to do without the flowers that year. These only appear on the one-year-old shoots anyway, which only develop after pruning.

  • Rejuvenation: Butterfly bush can be cut back without any worries, even once a year. Leave about the last 20 to 30 centimetres of the plant and always cut just above a bud or leaf axil. It is essential to use sharp, clean tools for this purpose so as not to create an entry point for pathogens and to allow the wounds to heal quickly. To prevent water from standing on the cut edge, always cut at an oblique angle.
  • Cut off faded flowers: Once the flowers have faded, it is worth removing the flowerheads before seeds form. Otherwise, the buddleia may quickly spread in the garden and all around. Although the young seedlings are quick to pull out, you can also save yourself this work. Simply cut back the wilted flowerheads to the nearest leaf axil. If you have removed the withered flowerheads in time, you can safely put them in the compost. However, if seed plants are already present, it is better to choose household waste for disposal.

In Europe, the butterfly bush or buddleia is considered invasive due to its ambitious tendency to spread. The exotic plant does not stick to garden fences, but invades the landscape, displacing native species. Despite this, the shrub should not be demonised. The name “butterfly bush” was given to the plant because it is a valuable food plant for butterflies and bumblebees due to its long flowering period and abundance of flowers, so buddleia definitely have added value for insects. Nevertheless, it is advisable to prevent uncontrolled spread, for example, by cutting off the wilted flowers. Although there are also sterile varieties, they are also worthless for insects. 

Buddleia growing from the pavement
Summer lilac should be prevented from spreading [Photo: Carmen Hauser/]

Naturally, there are numerous other plants that provide food for insects. If you would like to do something good for the winged pollinators, you can use insect-friendly seed mixes. These provide butterflies and caterpillars with a rich food supply.

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