In recent years there’s been plenty written and broadcast about pruning wisteria, but less about why midsummer is the time to train the plants. This is particularly important for both new and well-established specimens, and careful tying in and directing of some of the new growth is crucial to prevent the plants becoming a tangled mess of stems.
Act in July, when the growth is not so easily snapped but still pliable, and you’ll be able to create a well trained specimen. Left to their own devices, wisterias will create a vigorous tangle of new shoots. This is because they originated as forest plants, able to twine up the trunks and branches of trees to find the light. Once at the top, growth becomes much more restrained and as the shoots get well ripened in the sun, flowering spurs are produced.
Where to grow wisteria
When planting in the garden, it is important to choose a position in full sun – either on a south- or west-facing wall, fence or other support. This will ensure that the stems receive plenty of ripening, just as they would do at the top of a tree in their native habitat. I have mine growing in the open, on one of the brick columns supporting a wooden structure forming the ‘roof’ of an arbour.
Here all sides of the brick column gets full sun as it moves round through the sky during the day. When siting the wisteria, make sure that it will get plenty of natural rainfall, and make sure the soil is in good condition, but not over-enriched with too much manure or fertiliser. Too many nutrients will encourage excess growth which may be difficult to control and train.
How to train wisteria
The first key step with a young wisteria is to allow it to growth pretty much unchecked in its first season or two after planting. The plant will produce vigorous new shoots in the spring and early summer which can be tied in to supporting wires or trellis on walls and fences. My particular plant was initially trained up its brick column by twining the new growths in a clockwise spiral, holding it in pace with soft garden twine. The growths were trained and tied in separately so that they wouldn’t wrap around each other.
Such careful separation of the stems means that in years to come, the thickening branches will appear to snake sinuously over their supports, rather than strangling each other. Having reached the top of the brick column, I’ve now started to train the wisteria over the wooden part of the arbour. When training on a wall or fence, the stems are best spaced out at 20-30cm (8-12in.), growing them up and then horizontally to cover the space.
While the main shoots are being trained into the overall framework, any unwanted competition can be pruned back in the July and again in the dormant season. Leave the leading shoots unpruned so they can grow to the fullest extent required. The soft green sideshoots which they produce are best pruned back in July to channel the plant’s energy into the leaders, while at the same time starting to promote the flowering spurs which the mature plant will need.
What to do with established wisteria
Once trained to its fullest extent to produce a good framework, wisteria needs to be pruned twice a year to limit further growth and to promote flowering. This pruning is done in mid to late July, cutting the long growths back to around 4-5 buds above the point where they started into growth in spring. the second pruning is done in the dormant season, when the leaves have fallen from the plants, cutting back any regrowth to 2 buds from the base and tidying up any stems that were missed in the summer.
While all of this may sound like lots of work, it is well worth doing in the medium and long term. With careful training, tying in and pruning you’ll end up with a plant that not only looks stunning in flower, but which has a beautiful framework of branches when bare in the winter.