You're hardly alone if you're encountering the problem of wisteria failing to bloom. On the contrary, it's very common. You start to wonder after a while if you'll ever get to enjoy flowers on the vine at some point in this lifetime.
The answer may depend in part on which type of wisteria vine you're talking about.
Blooming of Different Varieties of Wisteria
Did you know that American wisteria vines tend to bloom more quickly than their Asian counterparts? Regarding the Asian wisteria, there are both Japanese (W. floribunda) and Chinese (W. sinensis) types.
But the information that follows assumes that you're already growing Chinese wisteria vines, which are immensely popular. How do you get them to quit dragging their feet and come into flower? There are at least four approaches you can try (they are not mutually exclusive, so you may wish to try more than one), involving:
- Pruning of the vines
- Root pruning
First of all, perform a soil test to determine any deficiencies in your soil. It's possible that your tree would benefit from a fertilizer high in phosphorus (the middle number in the NPK sequence on fertilizer bags) in early spring. It's important to note that wisterias are in the pea family, which means that they are nitrogen fixers. They don't need your help in obtaining nitrogen. In fact, excess nitrogen will only make your vine run more rampant and exacerbate the problem of "all foliage, no flowers."
You must perform a soil test before fertilizing though. If soil deficiencies are not the problem, adding fertilizer will over-fertilize the tree, which could then prevent your tree from blooming.
Also, try pruning a couple of times each year (in early summer after blooming and during dormancy in winter) to stimulate budding for next year. Regarding the latter pruning, NC State University advises that you, "Prune back old growth to three to four buds in late winter." These vines bloom on old wood.
If after years of failure in trying to get wisteria to bloom, you feel like you have nothing to lose and don't mind becoming more aggressive with your pruners, try pruning even more often. Some of the best success stories regarding getting Chinese wisteria to flower have touted a more-or-less constant pruning back of most of the new growth. A vigorous vine, it's almost as if it wants you to challenge it—and rewards you—if you do with a gift of flowers.
Root pruning in late fall is sometimes suggested too as a stimulant for stubborn vines that just seem to refuse to blossom! One home gardener reported that she had a Chinese wisteria that failed to bloom during the first two years she had it — which, she subsequently learned, isn't all that unusual (in fact, you'd be beating the odds if you managed to have flowers on a Chinese wisteria within its first five years). But she also found out that there's a way to stimulate the vine into blooming. Plunge a spade into the earth all around your Chinese wisteria (in about a three-foot circle), down to a depth of about a foot. Somewhat counter-intuitively, the resulting shock to the roots helps the plant to bloom, rather than hurting it.
Finally, evaluate the site where the wisteria vine is planted. Is it sunny? If not, that may be your problem (or at least a contributing factor). Wisteria likes to bask in the sunshine. If you've unwittingly selected a site for it that is too shady, your best bet may be to transplant it to a location that receives more light.