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Along with certain pests and diseases, there are a few other problems that might be behind the cause of the leaves on your Wisteria turning yellow or wilting. Common diseases that will affect your Wisteria include honey fungus and Phytophthora root rot and these are both root diseases. Waterlogging can also lead to root rot which in turn will cause both the wilting and yellowing of leaves. Another one, and one I have personally had issues with when growing wisteria in pots, is vine weevil, and this is because their larvae feed on the roots. Finally, the Wisteria scale can also cause yellowing and wilting leaves when the infestation is more serious.
Read on to learn more about some of these possible issues and, more importantly, what you can do about them.
Pests and diseases
I have a detailed guide called Wisteria pests and diseases to watch out for. Most pests and diseases discussed can turn the leaves on your Wisteria yellow and cause them to wilt. My guide details what to do for each pest and disease problem. Focus especially on scale insects, powdery mildew and root rot because these are the most common problems.
Lack of sun
Wisterias grow best when they are planted in full sun, this is a location where they will receive four to six hours of direct sunlight per day. Any less than this (partial shade) and flowers won’t bloom as readily. And being planted where they receive even less sun than they do when they are partially shaded means that the Wisteria can’t generate enough energy to produce foliage. The leaves can start to turn yellow and may even wilt, especially if they also become dry.
What to do
Try to arrange its environment so that the Wisteria receives more sun per day. Remove any plants or temporary structures that shade it. Ideally, from the get go, it just needs to be planted in a sunny position.
Wisteria leaves turning yellow (or wilting) can be the result of both over or under-watering. Watering the plant too much can lead to water-logging the soil which, in turn, creates the perfect environment for the root rot fungal disease (see the Wisteria pests and diseases to watch out for article for more information). This disease eventually leads to the plant not receiving enough water and nutrients, with the leaves failing because of this.
On the other hand, not watering the plant enough has the same effect, especially if they’re grown in pots.
What to do
Review your watering schedule and only water again when the top 3cm or so of the soil is dry. And check after each watering session that the soil doesn’t become water-logged. Don’t forget that poor draining soil can also cause root rot which leads to yellowing leaves and wilting.
If the soil in which your Wisteria is planted is full of nutrients, you shouldn’t need to fertilise it beyond the once-a-year application in the spring, but in all honesty, most people won’t even need to do that. However, Wisterias grown in pots are water and nutrient hungry. Any fertiliser that you apply is frequently washed out through the soil by water.
What to do
Regularly, even every couple of months over the summer, give your potted Wisteria some fertiliser. A fertiliser intended for roses or shrubs is a good choice.
See our article on growing Wisteria in pots and containers for more information.