Pruning butterfly bush: when and how, by species or situation

A butterfly bush (Buddleja davidii) is pruned hard once a year, in early spring: in March or April, when the severest frost has passed and the lowest buds begin to swell. Cut all branches back to 30 to 50 cm above the ground, just above a healthy bud. If you want a taller shrub, stop at 60 to 80 cm. The shrub flowers on new wood, so the better you prune, the more young shoots and the more flower clusters you will get from June into autumn. In summer you only cut off spent flower clusters. Buddleja alternifolia and Buddleja globosa differ, as shown per species in the table below.

Pruning butterfly bush by species and situation

Common butterfly bush: one hard pruning per year

The common butterfly bush grows quickly: without pruning you will get long, floppy branches after a few years that only flower at the top and the shrub becomes bare at the bottom. Because it flowers on this year's wood, you can cut it back substantially every spring. A mature shrub goes back to 30 to 40 cm, a young plant you keep at 40 to 50 cm so it first builds a sturdy framework. How to tackle this and what tools you need for thick branches, read in Hard pruning Buddleja davidii. Within a few weeks the new shoots appear and by summer the shrub is full again.

March, April or May?

Guides differ on the precise month. In Hard pruning Buddleja davidii the major pruning falls in March, in when to prune butterfly bush in April, at the moment when the lowest buds swell and a green tip becomes visible. That bud test is the safest measure: if it is still severely cold or you see nothing moving yet, wait a week. If you have missed spring, it can still be done in May, as described in pruning butterfly bush in May. The flowering then shifts somewhat. After May you no longer prune hard.

Buddleja alternifolia and Buddleja globosa

Not every butterfly bush flowers on new wood. Buddleja alternifolia flowers in May and June on last year's wood. If you prune it hard in March, you cut away all the flower buds. Therefore prune it immediately after flowering, as explained in Pruning Buddleja alternifolia. The orange ball butterfly bush, Buddleja globosa, requires only light pruning: dead wood and crossing branches away and shorten overly long shoots, see Pruning Buddleja globosa.

In pots and against self-seeding

A butterfly bush in a pot is also pruned in March, to 40 to 50 cm above the pot rim, and you keep it in shape with regular water and feeding. The details are in Pruning Buddleja in pot. Every butterfly bush forms abundant light seed after flowering that travels with the wind. Therefore cut off the spent clusters before the seed ripens and dispose of them with household waste, not on the compost heap. When to do this per species, read in Buddleja against self-seeding. If you are still looking for a sunny spot for a butterfly bush, try it out first in a garden design of your own garden.

Step-by-step plan

Step 1: Choose the moment in spring

Wait until the severest frost has passed, in March or April. Look at the lowest buds: if they are swelling and you see a green tip, it is time. Prune on a dry day.

Step 2: Prepare the tools

Sharp secateurs for thin branches, loppers for branches up to approximately 15 mm and a saw for thicker wood. Clean the blades before you start.

Step 3: First remove dead and weak wood

Cut dead, brown branches back to the base, as well as branches thinner than a pencil and branches that hang downwards or cross others.

Step 4: Cut the rest back to 30 to 50 cm

Prune each remaining branch back to 30 to 50 cm above the ground, at an angle and approximately half a centimetre above a healthy bud. Keep a young plant at 40 to 50 cm. For a taller shrub you stop at 60 to 80 cm, as in when to prune butterfly bush.

Step 5: Clear up and let it grow

Remove the prunings and give some compost around the base. Until flowering you do not prune anymore: every shoot you cut now is one flower cluster less.

Step 6: Cut off spent clusters in summer

After flowering, from August to October, cut off the spent clusters to the first healthy leaf. This gives new flowers and prevents self-seeding.