To prune wisteria during the first and second years of growth, tie the strongest branches to a supporting frame, and cut away unwanted growth twice per year. After the second year, or after the main branches of the wisteria are well-established and growing in the desired direction, cut the main branches to fit in the desired space, and trim the offshoots to encourage flower production.
Wisteria is typically pruned in July or August and again in February. Tie the main stem of the plant to a support, such as a fence, and cut away all except three to five of the strongest offshoots extending from the main branch. Secure the selected offshoots to a wire frame with garden jute.
Remove shoots growing on the base of the plant, and remove new shoots as they appear during the growing season. When pruning the plant during the first winter, cut back the main branch to 30 inches above the highest offshoot, and cut the offshoots back by one-third.
From the third year onward, continue to prune the plant as before, but trim back the flowering branches to three to five buds per offshoot during the summer. Trim back the offshoots and tree during the winter, reducing the number of buds on each offshoot to two or three buds per branch.