PRUNE WISTERIA
iF you have a wisteria and haven’t given it a summer pruning, do that this weekend. mature plants will always flower more prolifically if pruned at least once each year.
august is the month for dealing with all long, whippy growths. shorten each of these, leaving stumps with six to eight buds. in response to this treatment, most of the stumps will produce flowers next spring.
on young plants, or if you want to train your wisteria over a greater area, gently tie some of the long growths onto the supporting structure. prune all unwanted long stems as described above.
The RHs also recommends clipping wisterias a second time in January, shortening the stumps further. if you want to do that, reduce each stump to two or three buds next winter.
if your wisteria performs poorly, pruning like this could help. To bloom freely, wisteria needs to grow in full light, preferably on a south or southwest-facing site. Wisterias can also fail to flower if grown from unselected seed rather than a named, grafted variety.
sometimes, suckers grow up from the rootstock and will usually be more vigorous than grafted ‘scion’.
When that happens, the graft may fail or the less vigorous growth of the named variety becomes smothered by shoots from the rootstock, so remove any suspicious basal shoots.
The graft will be easy to detect — it’s a swollen zone on the trunk, close to the ground. shoots growing from below that graft will be suckers from the rootstock.