Varieties of Buddleja davidii can become very tatty if not properly pruned. If you leave buddleja unpruned, the only thing you see at eye level is a twiggy tangle of bare stems, with the blooms held at the tips of the stems, way above head height. They will also grow very large.
Discover 10 buddlejas to grow.
If hard pruned in early spring, the most vigorous varieties will still grow to 3m tall and 2m across by summer, while the smaller forms, such as ‘Nanho Blue’, can be kept to less than 1.5m in height and spread. Prune in mild weather.
There are exceptions to the rule. Buddleja alternifolia and Buddleja globosa bloom on stems made in the previous season, so cutting back in spring would remove the flower buds. Neither should be hard pruned – instead, cut out a selection of the oldest branches completely in midsummer.
Follow our simple step-by-step advice on pruning buddleja, below.
You Will Need
- Pruning saw
- Long-handled loppers
Start pruning buddleja when it’s coming into growth in early spring. First, trim back the top growth to around half its height using secateurs. This makes it easier to see what you’re doing as you progress, and gives you better access to the base of the plant.
Cut through the thick woody stems, around 30cm above the ground, using a pair of loppers or a pruning saw. Where possible, prune just above a bud or growing shoot. If you’d like the plant to grow taller than 3m (for example, if it’s at the back of a border), leave the stems up to 60cm long.
Remove any dead stubs and branches using the pruning saw or loppers. Cut these back flush with the main trunk to minimise the chance of dieback. Also thin out any crossing branches to prevent rubbing, and remove any thin twiggy growth sprouting from the base. Don’t worry that you’re being too brutal, as buddleja is so vigorous that it will quickly re-grow.
Aim to produce a short, strong framework of five to six main branches. It doesn’t matter if you can’t see many green shoots, as buddleja will produce new growth from underneath the bark. Fork lightly around the base to relieve any compaction you’ve caused by walking on the soil, and apply a mulch to the soil surface to retain moisture and suppress weeds.
Pruning in May
You can encourage buddlejas to flower later in the season, by cutting them down to the ground in May. This benefits butterflies such as the small tortoiseshell.