Wisteria needs a winter and a summer prune. Here’s how to do it, plus other tips for keeping this popular plant happy
Houzz UK contributor and award-winning landscape and garden designer. Claudia de… More
Pruning wisteria can cause some people to panic, as they feel they may damage their plant, but this climber is surprisingly forgiving. Left to its own devices, wisteria will grow rampantly, producing a mass of leafy growth at the expense of any flowers. So as long as you remember to prune twice a year, in January/February and July/August, you will encourage the plant to produce flower buds rather than diverting its energy towards making foliage.
When and how to prune
A wisteria plant left unchecked will not flower as freely as one that’s pruned twice a year. Once the plant has finished flowering, it puts all its energy into producing lots of new green tendrils.
In January and February, wisteria is leafless and in its dormant phase; this makes it the best time to prune the plant before the growing season begins. Pruning at this time of year will ensure the flowers are not obscured by leaves. Prune back to two or three buds, shortening the summer pruned shoots further to around 6-8cm of older wood. Cut back any long, whippy shoots that grew after the summer prune to just above a bud and around five buds back on the main stem. Tie in remaining shoots to form a framework.
In summer, pruning wisteria will allow more light to reach the base of the plant, provide better air circulation, and remove any vegetative growth to create short flowering spurs. Cut back to five or six leaves from the main branch.
A beginner’s guide to pruning
Dealing with out-of-control plants
Older plants that have got out of hand need hard pruning or rejuvenating, especially if the plant is growing over a window or has become too big. Where no pruning has taken place, you’ll often find the stems have swollen and got behind gutters, pushing them away from the house. The idea of hard pruning is to create a framework of evenly spaced branches so you don’t end up with a tangled mess.
Wisteria can take a hard prune. You can easily remove sections of older stems as long as you trace back to just above a young, healthy branch lower down. Tracing back is particularly important on plants that have become twisted over time, but you may want to space out your hard pruning over a couple of years on an old, neglected plant to give it a better chance of surviving.
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Where to plant wisteria
Wisteria is not self-supporting and needs a structure of some sort to grow up or against. On the whole, it’s easier to control and look after a wisteria planted against a wall or structure where maintenance can easily be carried out. Over the years, the plant will develop a strong spur system, which carries the flowers in spring.
For a wall, choose Wisteria sinensis (Chinese wisteria) varieties, which flower twice a year in May and June. W sinensis ‘Prolific’ is a good blueish colour, and W sinensis ‘Jako’ is a pleasing pure white form.
Some varieties look lovely with their long racemes draped over a pergola. The floribunda (Japanese) varieties are best for this, with W. floribunda ‘Macrobotrys’ being a good choice.
If you have a small garden, you could look at training a wisteria into a standard tree. Choose a shorter variety with stockier racemes, such as W. floribunda ‘Domino’, plant a single stem plant and put a stout stake next to it. Make sure you let the plant’s leader grow up straight against this support and, in February, and once it has reached the top, remove the tip to encourage side shoots. Each winter, prune the side shoots to around 15cm to form a head of flowering spurs.
Helping your wisteria to flower
If you buy a named cultivar that’s in flower at the time of purchase, then you have more chance of having a plant that will continue to produce flowers. Wisteria grown from seed can take between 15-20 years to flower.
Wisteria can sometimes still take a couple of years to bloom again, even when bought while in flower. You may notice you have no flowers for the first two years, but you shouldn’t worry too much – once the roots are well established, it should settle. If it doesn’t, you may need to start again.
As most wisteria are grafted onto stronger, less floriferous forms, it’s best to cut out all the long green spindly tendrils and growth at the base of the plant below the main stem. If you do this at the time of pruning, this will avoid the original plant from taking over and outgrowing the grafted variety.
Weather conditions can affect flowering, too. Dry soil in the summer means you need to keep an eye on making sure your plant is well watered, as this can affect flowering. Sharp spring frosts may also prevent flower buds forming and lead to buds dropping.
Wisteria, like many other woody plants, is propagated by grafting. If this graft union fails, which can be hard to spot and can also happen some years after planting, then the main stem will break off, leading to dieback and poor growth. When graft failure occurs, the top of the plant will tend to look as if it’s dying off.
The rootstock on a plant that’s had graft failure will remain alive and produce suckers, but it’s not worth keeping the plant, as it will end up being of inferior quality. The best way to tell if the plant has graft failure is to cut into it vertically through the graft union and you may find dark cork tissue.
As well as graft failure, there are root diseases such as Phytophthora root rot and honey fungus, which can also cause the plant to fail.
What you should do in the garden in February
Choosing your plants
When buying a wisteria plant, be sure to check the graft union. What you’re looking for is a clean, undamaged joined union with no sign of decay or any suckers coming up from the rootstock.
When you plant a young wisteria, make sure the graft union is proud of the soil, and don’t plant it too deeply. As soon as you plant, cut all the basal growth back to the main stem to ensure the whippy growth is removed.
Plant your wisteria in a sunny position, or light shade, in moist, well-drained soil with some good, well-rotted organic matter in the hole. As wisteria are long-lived plants that produce thick woody stems, make sure you plant them where they won’t need to be moved.
What experiences can you share about growing wisteria? Tell others your tips or ask for theirs in the Comments section.