My healthy, 10-year-old wisteria isn’t blooming. What’s the secret for making this vine flower? — J. Lockhart, Bloomfield, CO
Sometimes wisteria are vegetatively hardy—meaning the stems and leaf buds make it through winter in good condition, but their flower buds are less hardy and might not survive. Most wisteria are hardy to USDA Zone 5, but flower buds may be vulnerable to spring frosts if they’re not planted in a protected site.
Wisteria need good soil drainage and quite a bit of sunlight to bloom well. If the location is too shady, flowers won’t develop. Improper pruning also interferes with flowering. Prune new shoots back each summer to keep them from rambling out of control.
Wisteria do not bloom well in rich or overfertilized soil. They will put on tons of leafy growth rather than flowers. Fertilize lightly in fall, not spring. If you’ve been fertilizing heavily to encourage your plant to blossom, you may have made the situation worse.