How do I prune wisteria?
The two-cut-a-year system that turns rampant growth into flowering spurs, and why wisteria pruned once a year flowers badly.
- Difficulty
- intermediate
- Time
- 2 hr
- Read
- 3 min
Short answer
Cut twice. In July or August shorten the whippy new side shoots to about five or six leaves. In January or February shorten those same shoots again to two or three buds. That converts leaf growth into short flowering spurs, which is the whole point.
Wisteria flowers from short spurs on old wood, not from long new growth. Left alone it puts everything into extension growth, covers the gutter, and flowers sparsely at the top where nobody can see it.
What you'll need
- Secateurs
- Loppers
- Ladder or long-reach pruner (optional)
Step by step
- Identify the framework.The permanent structure is the main stems trained along wires or a wall. Everything you cut is the side growth coming off it.
- Make the summer cut in July or August.Shorten every whippy new side shoot back to about five or six leaves from the main stem. Do not cut the framework or any shoot you want to extend it.
- Tie in any shoots you need for extension.If the plant has ground to cover, select the strongest new shoots, tie them where you want the framework to go, and leave them full length.
- Make the winter cut in January or February.Go back over the same shortened shoots and cut them again, to two or three buds — roughly 75 to 100mm from the main stem. The fat buds are flower buds.
- Learn to recognise the flower buds.In winter, flower buds are noticeably fatter and rounder than the slim pointed leaf buds. Cut so you retain the fat ones.
- Remove suckers from the base.Grafted wisterias throw suckers from the rootstock which will never flower well. Pull or cut them off flush at the base whenever they appear.
- Renovate an overgrown plant in winter.Cut the tangle back hard to a chosen framework in winter. Expect strong regrowth and a year or two with little flower while the spur system rebuilds.
- Feed with potash, not nitrogen.Sulphate of potash in spring encourages flowering. High-nitrogen feeds and nearby lawn fertiliser produce vigorous leaf and no flowers.
- Be patient with a young plant.Seed-raised wisteria can take fifteen years to flower and may never flower well. Buy a named grafted variety in flower if you can.
Tips
- Two cuts a year: five or six leaves in summer, two or three buds in winter.
- Fat round buds in winter are flowers. Slim pointed buds are leaves.
- A wisteria bought in flower is a grafted plant; one bought cheap and unnamed may be a seedling that never flowers.
Common mistakes
- Pruning once a year only — The summer cut is what checks extension growth and initiates the spurs; the winter cut refines them. Doing only one gives a plant that grows enormously and flowers thinly.
- Feeding it with a general or lawn fertiliser — Nitrogen produces the long leafy growth you have just spent two prunings trying to prevent. Potash is what supports flowering.
If it doesn't work
Masses of growth, very few flowers
Cause: Not pruned twice a year, or too much nitrogen — Fix: Start the two-cut regime and switch to sulphate of potash in spring.
Flowers only at the very top
Cause: All the spurs are at the ends of unpruned growth — Fix: Prune back to the framework over a winter and rebuild the spur system.
Buds forming then dropping
Cause: Late frost, or drought the previous summer — Fix: Water well in summer when buds are forming; there is no remedy for frost after the event.
Vigorous shoots from ground level that never flower
Cause: Rootstock suckers on a grafted plant — Fix: Remove them at the base as soon as they appear.
Questions people ask
When do I prune wisteria?
Twice — July or August to shorten new side shoots to five or six leaves, and January or February to cut the same shoots back to two or three buds.
Why does my wisteria not flower?
Most often no summer pruning, too much nitrogen, or a seed-raised plant that is simply too young. Grafted named varieties flower within a few years; seedlings can take fifteen.
Can I cut an overgrown wisteria back hard?
Yes, in winter. It regrows strongly. Expect one or two seasons of poor flowering while the short spurs rebuild on the new framework.