Wisteria, with its captivating purple blooms, is a climbing plant that demands careful pruning. This cottage-garden staple is known for its aggressive and expansive root systems, which can grow deep and wide. When left untamed, the roots will seek out any available crevices or cracks in foundations to penetrate and potentially cause structural damage.
But pruning wisteria is important not only to control the plant’s vigour but also for gardeners seeking to maximise its flowering abilities. Most people know they need to trim wisteria in August when the flowers are at their peak, but they can make the mistake of cutting back too much.
This will strip the vine of more stunning blooms, though it’s easily prevented by following one straightforward rule, according to National Greenhouse’s indoor gardening expert, Tom Hilton.
He explained that the ideal length for wisteria pruning is five buds, highlighting how crucial proper trimming is.
Tom advised keen gardeners: “After your plant has begun to flower, around July or August time, it’s time to break out your clippers and get to your garden.”
The gardening expert continued: “Pruning around five buds is a great amount, as it leaves plenty to continue growing while encouraging flower growth, rather than a continued expansion of the plant itself.
“It’s also the best way to keep your plant in check, not just to prevent it from overgrowing, but also to keep it looking tidy and presentable.”
Trimming wisteria isn’t simply about promoting fresh growth; it has a major effect on the plant’s structure as well.
Annelise Brilli, part of the horticulture team at Thompson and Morgan, agreed: “Without pruning, wisteria will grow into a huge, tangled vine composed mainly of very long stems clothed with leaves.
“Pruning controls these highly vigorous climbers, concentrating growth into a permanent woody framework covered in masses of short side shoots which will be crowded with flowering buds.”
However, she cautioned against taking the five-bud rule literally, emphasising that it’s generally equivalent to around 20cm, which may be a better measure against short shoots.
These will be non-vigorous shoots that are naturally becoming woody and developing lots of flower buds by themselves.
As for the best time to prune wisteria, Tom advised gardeners to wait until the height of the blooming season to start cutting.
He clarified that August is the optimal time to prune wisteria as it effectively marks the end of the flowering phase and a natural pause in the growing cycle to give the plant a “refresh” in preparation for the emergence of new growth.
The National Greenhouse gardening expert added that pruning allows you to guide the growth of new buds on the path you want them to take, rather than them potentially taking over your garden or the side of your house.