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A trained wisteria vine provides attractive greenery and flowers, but an overgrown vine flowers poorly and becomes a tangle of dead or barren vines. Wisterias tolerate severe pruning, which allows you to regain control of the overgrown plant and return it to its former beauty. Pruning isn't done all at once so it may take up to a year before the old plant is pruned and trained back to a healthy growth habit.
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Cut back suckers growing from the base of the wisteria vine in late winter. Remove these at soil level. Leave one leader, or main stem, growing upward.
Trim away dead and damaged branches and side shoots in later winter. Cut these back to the nearest healthy wood or remove them at their base.
Prune back the framework, or lateral, branches in summer after the wisteria blooms. Cut these back to approximately 12 inches long, making the cut within 1/4 inch of a healthy bud.
Remove any crowded lateral branches that aren't growing along the wisteria trellis. The remaining lateral shoots should be spaced 14 to 18 inches apart.
Head back the top growth. Cut the top of the main upright vine down to a 4- to 6-foot height.
Insert the blade of a spade into the soil, cutting a circle into the ground around the trunk in fall. Make the cuts 4 feet away from the base of the main trunk and push the spade blade about 18 inches into the ground. This method of pruning, called root pruning, prevents the wisteria from growing too tall and encourages flowering the following year.
Check the wisteria trellis after you prune. Replace any stakes or wires that are old or broken to ensure the trellis can still provide support to the plant.
Prune the wisteria annually in summer once you have the plant back under control so it doesn't overgrow again.