Stratford Ontario. When should I winter prune in this cold climate? Is April 1 too late? I have pruned in Sept. for the fall.
Thank you for your inquiry.
Few sights are more impressive than that of a mature Wisteria in full bloom. The trailing clusters of pea-like blooms are one of the highlights of the late spring or summer garden.
Wisteria flowers on lateral shoots known as lateral spurs that have developed off the main stems the previous years; also referred to as “old wood”.
The aim in pruning Wisteria is to create as many well-spaced spurs along a strong framework. This will allow the pendulous blooms to hang without crowding the blooms on the branches below.
Wisteria should be pruned twice a year: mid summer and late winter.
Since Wisteria flowers on “old wood” (previous seasons growth) you must “prune after bloom”. Pruning in the spring will cut of any flower buds that were formed the previous season. Therefore, in mid July, early August or two months after flowering is finished, prune all the twiners, (long, straight, thin branches) that have sprouted from the basic framework back to one to two buds. Each of these cuts will produce a spur covered with bloom. Lateral shoots are pruned to within 4 to 6 leaves (6in or 15cm) of the main branches again to form flowering spurs. Get rid of any branches that hang down and spoil the shape of the plant. To force the plant to branch more horizontally, make your cuts on a down-facing bud (even if you cut below this bud you will get new branches).
During late winter when the plant is dormant cut any un-pruned horizontal leader shoots back to one-half their length. Re-cut lateral shoots pruned the previous summer back leaving only two or three buds (3in or 8cm) for short flowering spurs. Remove any shoots coming out of the spurs.
Please refer to our Gardening Guide on How to Get Wisteria to Bloom for additional information on pruning principles and general care of Wisteria.
With proper pruning you will achieve spectacular blooms that will be enjoyed by all.