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Problems that you will experience with your Wisteria, such as graft failure and root diseases like honey fungus and Phytophthora root rot are either biological (pests and diseases), environmental (sun, location, etc.), or due to your care, for example, incorrect pruning results in no flowers. In this guide, I share my experience with all of these here and give advice on what to do about each of them.
I’ve already addressed specific problems in some of my other informative guides, Why is my wisteria not blooming? and Why are my wisteria leaves turning yellow or wilting? so if these are the problems you are experiencing, you might find the above two guides helpful.
Pests and diseases
Pests such as scale insects and diseases such as honey fungus affect many plants, and Wisteria is not immune to them. Our guide on Wisteria pests and diseases to watch out for details on some of the common ones to look out for on your Wisteria plant. It also has information about what to do about each individual pest and disease.
There’s also a detailed specific guide about the Wisteria scale insect. They are becoming more common and are larger than other scale insects, they have blackish-brown shells which are 10mm wide. They can also suffer from other scale insects, but these are usually smaller (5mm) and light brown or grey.
Wisteria graft failure
In the guide Growing Wisteria Amethyst Falls, I recommend buying a Wisteria plant that’s been propagated by a cutting or has been grafted from the original plant, most Wisteria is grafted to a rootstock. This is still the advice to follow, although sometimes the grafts have been known to fail – even after many years of strong and healthy performance from your Wisteria. I have seen some Wisterias where the grafts have unfortunately failed after 20 years.
When this happens, the graft has often decayed. The graft is usually close to the soil level so look for any problems there. Another easier-to-spot clue that causes this problem is that new shoots appear from below the ground while the top of the plant dies back. The new shoots are developed by the rootstock and not the grafted part of the plant.
What to do
When the rootstock has failed, unfortunately, there is nothing you can do but dig up the Wisteria and replace it with a new plant. The shoots coming from the rootstock are not the original plant.
There are so many things that can be incorrect with the plant’s location, soil, sun and other environmental factors. It’s quicker to read what to do right rather than what not to do.
What to do
To find out the best circumstances to grow Wisteria in, it’s well worth reading my guides on Growing Wisteria Amethyst Falls and Growing Wisteria in pots and containers. The quick answer is that they prefer fertile, well-drained soil in a sunny position. They also benefit from pruning twice a year, once in July/August and then again in January/February.
Yes, you may do things that cause problems for your Wisteria plant without really realising it. This can be from not watering them enough when buds are forming in the previous year to incorrect pruning.
Both over- and under-watering your Wisteria have the same final effect on your plant. The leaves turn yellow and wilt, and finally, fall off. Along the way with over-watering, phytophthora root rot may set in and destroy the very foundation of your plant.
What to do
Only water your Wisteria when the top 3cm of soil is dry. Ensure that the excess water is draining away fully and the plant doesn’t become water-logged. When growing them in pots, this means making sure there are drainage holes and they are covered with crockery to prevent them from becoming blocked up. If planted in the ground and you notice that the soil sometimes becomes waterlogged, dig plenty of horticultural grit and organic material into the ground to improve drainage. Mulch well around the plant (but not too close to the trunk) to help with water retention.
Remember that Wisterias that are being grown in pots and those that you grow up a wall dry out quickly and will need much more frequent watering.
Wisterias need some care and attention in deadheading and pruning. Remove the blooms as soon as they’ve faded to encourage new flowers to grow. And make sure to prune the vines twice a year (spring and autumn) to keep the Wisteria under control and promote more flowers. A Wisteria plant left unattended can create all kinds of problems (see Will a Wisteria damage my house?) and look unsightly.
Our guide on how to prune your Wisteria gives the details of this essential pruning task, if you prune them incorrectly, you can remove the flowering shoots for the following year and get no flowers.