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.
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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.
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Follow our simple step-by-step advice on pruning buddleja, below.
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.