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How do I prune a wisteria vine?
Wisteria may be grown as a vine, a tree or a shrub. This presents options to be grown as a vine against a wall, fence, trellis or arbor or coaxed into a tree. With more severe pruning, it can be maintained as a shrub.
Pruning to stimulate flowering is involved and can be time-consuming, but once understood and mastered it can become part of your regular pruning chores. One caution: over watering or over fertilizing reduces the chance of getting a wisteria to flower. The best times for light feeding are in late winter or mid-spring.
Pruning should begin with the removal of all dead, broken, diseased or problem limbs to the point of origin or back to a strong lateral branch or shoot. Then, for a young plant, train it by thinning the number of shoots and cutting back lateral branches in order to develop the desired size and shape. Pruning in late winter or early spring before growth begins, is good for training a young plant. The most damage may be created by pruning immediately after new growth begins in the spring.
Once your wisteria has grown to its desired size regular summer and a late winter pruning is required. Begin my cutting the new shoots that develop in early summer back by ½ when they are about 2 feet long. New shoots will grow from these 1 foot “stubs.” Cut these new shoots back by half when they are 2 feet long. Continue pruning this way throughout the summer. You may have to prune 3-4 times as the new shoots grow. Then, in late winter around February cut back the COMPLETE shoot that grew the past year to within 4-6 inches (about 3-4 buds) from the main stem. This means that after your late winter pruning you are only leaving 4-5 inch stubs of growth from the past year. The regular summer pruning to remove summer foliage encourages the flower buds to form close to main stem where growth began that year. The late winter pruning preserves the flower buds but reduces the number of buds that will develop foliage for the coming year.
Over time this pruning will cause plants to form dense clusters of twigs from the constant cutting back. Some of these woody twigs can be removed right after flowering to prevent over crowding or at the time of your late winter pruning if you don’t mind sacrificing a few flowers.