Butterfly bush lilacs are vigorous and attract countless insects to the garden. However, the lilac needs regular pruning to produce large flowers and a beautiful crown.
If you have a butterfly bush (Buddleja davidii) in your garden, you can be sure that the pretty insects will come in droves to sip nectar. The undemanding flowering shrub grows in practically any soil as long as it gets enough sun. To ensure that the beautiful, fragrant flowers of the butterfly bush unfold anew every year, the flowering shrub should be pruned regularly. But when do you do it and how do you go about it correctly?
Should butterfly bushes be pruned after flowering?
The butterfly bush (Buddleja) is a flowering shrub that blooms on this year’s wood. It is extremely vigorous and very tolerant of pruning. Contrary to popular belief, butterfly bushes are not pruned in summer directly after flowering like normal lilacs, but in late winter. On a frost-free day in January or February, cut off all the old shoots. Leave 20 to 30 centimeter long stubs from the branches, each with two eyes. The shrub will sprout new shoots from these. In this way, the summer lilac forms two new branches on each shortened shoot.
If the lilac is pruned regularly, it becomes fuller and fuller and produces plenty of flowers. Do not prune the butterfly bush too late. The sprouting from the dormant eyes takes time. If you wait too long before pruning, flowering will be delayed until late summer.
Loosen up summer lilacs
The problem with regular pruning and the lilac’s vigor is that the shrub becomes increasingly dense over the years. The heavily branched whorls of branches need to be removed from time to time. Sometimes branches grow in and on top of each other. Such interfering branches and weak side shoots should be pruned directly at the base. For a beautiful, loose crown structure, you should not prune all branches to the same height, but to different heights. This way, the shrub will not develop quite as many flowers, but it will also grow less densely.
Prune out after flowering
After flowering in summer, you should cut off the wilted flowers of the butterfly bush as soon as possible. This not only saves energy during growth, it also prevents the flowering shrub from seeding. As butterfly bushes self-seed very easily and are even considered invasive, it is advisable to remove the inflorescences in good time. Cut off the old flowers above the first leaf axil. If seeds have already been planted, you should dispose of the flowers in the household waste rather than in the compost. The seeds are stubborn and may otherwise end up in the compost next year.
Pruning butterfly bushes correctly
Always use sharp and clean tools when pruning butterfly bushes. The wood of the lilac is very brittle and can only be cut cleanly with good pruning tools. A smooth cut surface protects the plant from the penetration of pathogens and fungi. Tip: Always cut the branches at an angle. This allows rainwater to run off and the wood to dry quickly.
Pruning for the alternate-leaved summer lilac
Unlike the butterfly bush, the alternate-leaved summer lilac (Buddleja alternifolia) forms its flower clusters in the leaf axils. Buddleja alternifolia flowers on last year’s wood and should therefore not be pruned in spring, otherwise it will not flower. Due to its overhanging growth, this shrub rarely needs pruning. If the lilac has become too dense, old and damaged branches can be thinned out at the base in late summer.
