Lilac, particularly the summer lilac (Buddleja davidii), is known for attracting butterflies with its abundant nectar, earning it the nickname butterfly lilac. This hardy flowering shrub thrives in nearly any soil as long as it receives plenty of sunlight. To ensure the beautiful, fragrant flowers bloom year after year, proper pruning is essential. So, when and how should you prune?
Pruning Butterfly Lilac: Timing Matters
Unlike traditional lilacs that are pruned after flowering, the summer lilac should be pruned at the end of winter—specifically in January or February—on frost-free days. Cut back all old shoots, leaving stubs that are 20 to 30 centimeters long on each branch, ideally with two buds. This encourages the shrub to grow back with two new branches from each cut shoot.
Regular pruning results in a blooming display that becomes increasingly abundant over the years. Avoid pruning too late, as dormant buds need time to develop; delaying too long can push blooming to late summer.
Thinning Out Summer Lilac
As your summer lilac matures, it may become dense. To maintain an airy structure, remove overcrowded branches that grow into each other. Cut away interfering branches and weak side shoots at their base. For a balanced appearance, avoid uniform cuts; instead, prune branches at varying heights. While this may reduce the number of flowers, it will create a less dense shrub.
Removing Faded Flowers
Once the butterfly bush flowers fade, they should be removed promptly. This practice conserves energy for new growth and prevents the shrub from becoming overly invasive through self-seeding. Cut off the spent flowers just above the first leaf axil. If seeds have already formed, dispose of the flowers in household waste rather than compost, as they can persist in the compost.
Important Pruning Tips
Always use clean and sharp tools when pruning butterfly lilac. The wood is fragile and requires a clean cut to prevent disease and fungal infections. Remember to cut branches at an angle to allow rainwater to drain, aiding in quick drying.
The Exception: Alternate-Leaved Lilac
The alternate-leaved lilac (Buddleja alternifolia) differs from the summer lilac in that its flowers form in the leaf axils and bloom on last year’s wood. Therefore, avoid pruning in spring, as this will inhibit flowering. Due to its overhanging growth habit, pruning is rarely necessary, but if the shrub becomes too dense, you can thin out old and damaged branches at the base at the end of summer.
By following these guidelines, you can ensure your lilac remains healthy and vibrant, showcasing its stunning blooms for seasons to come!
