If that’s one plant that’s more than likely to get us into a tied up pickle on how to prune is certainly a wisteria. Wisterias seem to have long tentacle like growths that wrap around everything in its path indeed I wonder if J K Rowling thought about wisteria when she came up with Devils snare in Harry Potter and the Philosophers Stone. Wisteria is actually pretty easy to train and prune, you just need to remember a few things to get the best from it
First the growth
wisteria tend to put on two types of growth, flowering growths that tend to be a short in length up to about 15cm maximum and extension growth. The flowering growths are indeed where the flowers will be borne from May onwards and the extension growth is what helps the plant to expand both in height but also these stems are designed to fit into rock spaces, expand and root and so forth produce another plant. This is part of the reason they love getting underneath slates and tiles.
The shorter growths, these are the flower bearing growths
The longer extension growths, these can be over 5m in length in some cases, also note the seedpods on the shorter growth.
knowing the differences between the two types of growth helps to know which ones to prune. It’s worth remembering also that wisterias can take up to 10 years to flower depending on how they are propagated, so if you can’t see any of the shorter growth on a younger Plant, it means it’s not old enough to flower yet.
It’s very easy with all this very long growth to just tie it in to the height that you want the plant to get too in the end. This ends up with a bare middle and all the growth at the top. It is worth taking time to allow the plant to fill up the gaps and build a frame work of branches up. This is done by reducing the young stems down in length to between 30-60cm. Why do this? Well whatever plant you prune it is the first 2-4 buds that will break. Having them break lower down the plant, will give you a chance to build up a frame work of branches over time. This pruning down to 30-60cm can carry on until the plant has cover the space with each new break treated the same. Once it has a good framework up or indeed the plant is already got a established framework, the extension growth should be pruned down to 3 buds above where it started growing last spring. This is done during the dormant season from December to end of February. If you need to summer prune from July onwards, prune back to 5 buds above the breaking point each time but when pruning in the winter, take these shoots hard back right down to 3 buds from where in broke in the spring. It may seem hard but by doing this, you will encourage more shorter flowering stems to form. If the plant is more established, just forget the 30-60cm training bit and cut straight to the pruning down to 3 buds. The buds on Wisterias are indeed opposite so need a slanting cut away from the bud, more information can be found on my pruning cuts blog here and part 2. Right enough words and onto the photos on how to do it
New growth being cut down to 30-60cm to help form framework branches from the base up. When planting it’s also worth untwisting all the stems as eventually they will strange each other
The extension growth being pruned back to 3 buds on an established framework branch.
A plant before pruning with all the extension growth going a little mad!
And afterwards with the extension growth pruned back to 3 buds and any new framework branches being trained in and cut back to approx 45cm.
This is why we prune them as per above, this is the same plant in flower, every cm of it is covered in flower without one area being bare. It took me 4 years to get it looking like this and it was planted about 6yrs ago now. Taking time to build the framework up is very important.
With older plants that haven’t had as much work done on them in the past, it is worth thinning out the older stems. I find it easier to compare them and after taking out the dead ones, remove the stems with the most length of bare stem or with the smallest amount of branches on. On a plant like this I would be looking at removing 2/3rds of the existing wood to open it up more and then start training in younger stems as a framework into the gaps. Some of the existing large branches can also be bent down to fill in the gaps as well.
The finished plant and you can see how much clearer and managed it looks now. It will take about another 2-3yrs to get the plant to its best
I hope you have found this blog on pruning wisterias helpful, if I can help any more, please feel free to comment below and I will try and answer the query as soon as I can