There are few sights more breathtaking than a mature wisteria in full bloom in the summer, its gorgeous trails of flowers in shades of blue, mauve, pink or white, adorning house walls or cascading over pergolas.
Yet so many gardeners struggle to get this gorgeous climber to flower year after year.
So often its refusal to bloom again is down to inadequate pruning. There’s still just time to give it a prune this year to stop it running riot and give it a better chance to come back stronger in years to come.
You have to be patient when planting a wisteria, as it may not flower for three or four years, provided it is planted in soil enriched with large amounts of organic matter, is watered religiously while establishing, and is placed in a sunny, sheltered position.
If you leave wisteria plants to their own devices, they can run riot, growing into huge plants which don’t produce any flowers and only succeed in ripping your drainpipes down and blocking the light from your house.
Pruning should be done in two stages – in summer, after flowering ends, and again in winter. If you have trained a line of main stems out along horizontal wires, by the third year there should be a framework of branches.
Stop the plant running amok by cutting the long tendrils and side shoots to 20cm (8in). This will encourage it to build up plenty of short spurs, so creating fewer leaves and more flowers. At the same time, cut the main stems back to restrict the amount of space they take up.
In winter, new growth will have sprung up, which will need keeping in check. Cut back the same laterals and side shoots to within two or three buds of the main branches. Always cut 2.5cm (1in) above a bud.
Old neglected plants may be pruned hard and will grow, with new shoots appearing from the base of the plant, but it’s likely to be a few years before they’ll flower again.
If you haven’t much space, wisteria plants can be grown as standards, effectively into small flowering trees, with spirally stems and masses of flowers.
Choose your wisteria carefully. The popular variety, W. sinensi, is a rampant grower with flowers 23cm (9in) long, but which can get out of hand (it can grow to 18m (60ft) tall) and is not a good choice for a house wall as it frequently gets into gutters and under roofs.
Go for a less invasive W. floribunda, Japanese wisteria, which grows to around 4m (13ft). The variety ‘Alba’ has white flowers with a lilac tint, or ‘Multijuga’ produces fragrant, lilac flowers on slender racemes.
Pruning a big wisteria may seem like a thankless task at first, but it may not take as long as you think. And the wealth of flowers you’ll enjoy next year will be well worth the effort.
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