Horticulture Magazine

How (And When) To Prune Wisteria

purple flowering wisteria tree in a garden

Learn how to prune wisteria to keep it healthy and looking its best.

Wisteria is a beautiful climbing plant – take care of it and it can really have a strong impact in your garden. But learning how to prune your plants is important. Wisteria, like many other plants, will look better and be healthier if you prune it annually, at the right times and in the right ways.

Pruning wisteria might seem a little complicated at first. So in this article, we will aim to demystify the process and help you understand the process and do it correctly in your own garden. Pruning is not always essential. But there are a number of reasons why you might wish to prune the wisteria that you have grown.

Why Prune Wisteria?

wisteria climbing up the outside of a house with a cleared window area
Wisteria

The main reasons to prune wisteria are:

  • To stop them becoming too large. Wisteria can outgrow their location and therefore reduce in vigour over time if not regularly pruned.
  • In order to keep their size in check, and make sure they do not crowd out other plants.
  • To improve light reaching new growth, so it grows well and flower buds form as they should.
  • For better flowering. Reducing the amount of foliage growth and encouraging short, flowering spurs means you will have more flowers on your wisteria.
  • For neatness and practicality. Pruning can keep wisteria on its support structures, not overly reducing light levels or preventing egress to different parts of your garden.
  • And it can breath new life into old, mature plants in need of renovation.

When to Prune Wisteria

Wisterias are typically best pruned twice each year. Once in the summer, in July / August, and once in the winter, in January / February. Renovation pruning when the plants are cut back much more dramatically can also be undertaken any time over the dormant period. (After leaves have fallen in autumn, and before new growth emerges in spring.)

Summer Maintenance Pruning

Standard summer maintenance pruning takes place after the wisteria has finished flowering. The main goal of this summer pruning is to control the size of the plant. You might wish to control the size of the plant to prevent it from getting into the guttering on your home, to prevent it from covering windows, or to prevent it from outgrowing a support structure on which it grows. Summer pruning will also ensure that light reaches the growth and that the plant does not put on excessive foliar growth at the expense of flowers.

In July or August, cut back each of the green, newer shoots of the growth from the current year to 5-6 leaves each.

Winter Maintenance Pruning

closeup of a hand pruning branch on a white background
Winter pruning

Winter pruning is mostly about making sure that the plant is tidy, in shape and healthy before the growing season begins. This work can be undertaken at any point while the plant is not in leaf and is within its dormant phase. But January or February is usually best.

Firstly, look for the three ‘D’s. Remove any branches or shoots which are dead, damaged or diseased, leaving the healthiest shoots behind. Then, you can also cut back the same shoots which were pruned in summer once more, to leave each one with just 2-3 buds.  This will help to keep the size and shape of the plant in check, and also help to reduce foliage shading on the flowers of the following season.

Pruning for Shape and Form

As well as thinking about the normal summer and winter maintenance pruning, you can also think about pruning for a specific shape or form.

Wisteria can be grown in different forms, and can be pruned in specific ways to suit the situation. For example, you might grow wisteria on walls and train it as an espalier. Espalier forms are a popular choice for fruit trees, but they can also work for many climbing plants – including wisteria.

Pruning for an espaliered wisteria should also be undertaken as above, twice a year. And over time, a strong spur system can be formed through selective pruning. New growth from the base of the plant can be cut off at the base, or trained for replacement shoots.

Wisteria which have long flowering racemes will look best if they are trained on structures which allow them to hang without being impeded by foliage or branches. Training these onto pergolas, or arch structures therefore can be a good idea. As well as thinking about the maintenance pruning described above, it can also be helpful to think about thinning racemes to give the best space to develop and dangle down to create a good display.

a wisteria arch on a garden pathway with hedging either side
Wisteria arch

Wisteria can also be positioned at the base of large, mature trees and grown into them. Pruning in these cases, however, can be challenging. It can be difficult to distinguish and reach the shoots you wish to prune when these are entangled in a canopy. In such cases, wisteria may largely be left to their own devices.

However it should be noted that the species can affect the growth of each other. A large and sprawling wisteria can swamp smaller trees, and when a tree has a dense canopy, this can affect how much the wisteria flowers. Pruning in such cases will often be hampered by practicalities of reach. But you should both the wisteria and the tree so as to maximise light levels for both and ensure their continued health.

If you are training a wisteria as a standard, in a container or in the ground, it is important to make sure there is a sturdy central support. The stem should be trained vertically up the support rather than twined for greater strength.

Once the growing tip reaches the top of the central support, remove the tip in February. This will encourage the formation of side shoots. The following winter, prune the side shoots to around 15 to 30cm. Repeat this process every winter to start to form the head of the standard form. As the head forms, prune shoots not needed to extend the head to around 7 leaves each summer, and cut them back harder in the winter as required.

Dramatic Pruning to Renovate Older Wisteria

In the case of older wisteria plants, more dramatic pruning may be required to renovate them, and to make sure they do not grow out from walls, or over windows, or spill off their supports. 

A wisteria which has not been pruned for some time may be overgrown and need some work. You will have to begin by identifying and removing sections of the plant which are not performing as well, or which are in the way.

You can cut back sections to a young, strong branch or shoot that is lower down, or, in extremis, even cut them back drastically to the main trunk, or even to ground level, where necessary. Take some time, and make a plan about which branches and shoots you wish to keep before you begin. Your aim should be to create a healthy and open framework of spaced out branches.

New growth can be trained in to replace older ones you have removed, and used to fill any caps in the framework. Once you have a framework you are happy with, you should then simply continue the maintenance pruning as above.

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