Q: We had a beautiful Wisteria creeping along the canopy of our mobile home. Every spring it was thick with purple flowers and lovely to look at. It wasn't as mature as some I have seen as it still had lots of green leaves amongst the flowers, where as many of the more mature ones flower first then the leaves come later. A couple of years ago we found "scale" on it and had to cut it right back to nothing. It has been a couple of years now and it has re-grown up the post and along the canopy again but the foliage doesn't seem as thick as it once was and of course there are no flowers. Is there there something we could do or a treatment we could give it to help it fill out more and flower for next year or is it just a
matter of maturity?
Flowering with Wisteria can be a problem for some people and there could be a variety of reasons why yours isn’t flowering.
Maturity – You mentioned this as one possible reason. This could very well be true, as your plant is experiencing new growth, and depending on the species of your Wisteria, could take up to 20 years to mature.
Lack of sunlight – Has the area around your vine changed in the past few years? The Wisteria needs at least six hours of direct sunlight for it to bloom. If possible, remove any items that are preventing your vine from getting enough sunlight.
Excessive nitrogen – The plant has nitrogen-fixing capability since bacteria around its roots give the plant plenty of nitrogen. If the nitrogen ratio in the soil is too high, your plant will stop blooming. Adding superphosphate (0-20-0) in early spring and potassium occasionally will aid your plant to flower.
Severe winter weather – The winter weather may injure or kill your flower buds. And unless we have the power to change the weather (what an awesome power to have!), I’m afraid there’s not much we can do about that.
Improper/heavy pruning in the winter and spring – I understand that you pruned a lot of your vine since you found “scales” on the leaves. Pruning the vine seems to encourage vigorous vegetative growth and discourages flowering. Root pruning can be a solution to this problem since it has been very successful in restoring blooming for older plants while stimulating blooming in young plants. Use a spade to cut vertically into the soil around 45 cm (18 inches) deep and about 1.2 m (4 feet) from the main trunk, all around the vine. This method, combined with regular summer pruning, should help your plant flower.
If you want to force your plant to flower, you can abuse the main trunk and put the vine through drought stress. Although these methods work well, letting your Wisteria flower naturally is best, so only use these two techniques as your last resort.