Pruning Buddleia (Butterfly bush)

(Question)

Hello, I have two butterfly bushes in a back garden that have thrived on neglect. I now realize I need to prune but I have read conflicting advice. Some say cut down stalks to just above soil, others 60 cms, still others above first growth? Which should it be?

Many thanks

(Answer)

Congratulations on having two butterfly bushes. I hope you have enjoyed the monarch butterflies flitting around the flowers in late summer!

With regard to pruning a well respected source of garden advice Michael Dirr, in Hardy Trees and Shrubs recommends “if plants become overgrown cut back to 12 inches (30cm) from the ground ….and fertilize, a handsome flowering shrub will be evident by midsummer.” In terms of when to prune this is different depending on the species of buddleia. B. davidii forms flowers on the current year’s growth. If this is the species you have then early each spring is the time to prune. Removing spent flower heads will also encourage new shoots and extend the blooming period.

B. alternifolia forms flowers on the previous year’s growth. Pruning for this species should be after the flowers have faded, when you should cut the flowering shoots back to within a couple of buds of the main plant framework.