How do you prune a Wisteria tree?

Wisterias should be pruned twice each year a/ to ensure plenty of flower bud, and b/ to keep this vigorous climber under control.





Autumn Pruning involves cutting all of the current side-shoot growths back to within 30cms of the main lateral. This should leave 4-6 leaves on each side-shoot. Obviously, any side shoot required to extend or train the framework should be left and trained as required.





Winter Pruning January/February, cut these side shoots back even further - 6-10cm long, leaving only 2 or 3 buds on the side-shoot. These will be the flowering spurs.





Both of these operations should be carried out each year. The only shoots to be left 'unscathed' are those which are required to extend the size or direction of the plant.





Wisterias can be left unpruned where space allows, but flower more freely if pruned in summer and winter to build up a spur system.





August: Shorten-back current season’s shoots to 30cm (12in). This allows more sun to get to the wood, encouraging flower-bud formation.





February: Shorten-back the summer-pruned shoots to within 2.5-5cm (1-2in) of older wood or two to three buds. It should be possible now to distinguish the plumper flower buds from the slimmer growth buds.





Long, whippy shoots that grew after the summer pruning (bottom right) should also be pruned. Cut these back to five or six buds from the main branch, making the cut just above a bud.








Aftercare


If a plant, established for several years and regularly pruned, fails to flower, try a spring application of superphosphate at 68g per sq m (2oz per sq yd) and sulphate of potash at 34g per sq m (1oz per sq yd). This should help to check any tendency to excessive leaf growth and encourage flowering, particularly in lighter, sandy soils where there is more likelihood of low potash levels. Wisterias need a sunny situation and where poor or non-flowering plants are growing in some shade flowering may be encouraged by reducing overhead shade.





Although showing good drought tolerance once established, it is advisable to ensure that plants, especially if against a wall, do not suffer from lack of water. Mulch in spring before the onset of drier weather conditions to conserve moisture, and water thoroughly and regularly during any periods of drought, particularly from late July to September when flower buds are being formed.





Renovation


If possible stagger this over a number of years, removing and replacing one main branch as required. Wisterias cut almost to the base re-sprout vigorously, but take many years to flower freely again.





Poor or non-flowering plants


Graft failure: Wisterias are propagated commercially by grafting cultivars onto seedling rootstocks. If the graft fails the vigorous rootstock grows, which produces little flower. Always check when purchasing plants that a healthy graft union is present. A clear join should be seen, 15-30cm (6-12in) above ground level.





Seed-raised plants: Wisterias sometimes produce seeds, but these produce plants of inferior quality which can take many years to flower.





Soil conditions: Wisterias need a sunny, sheltered position to flower well. Consequently they are often planted against dry, sunny walls. To retain soil moisture and help prevent bud drop the following year mulch in spring and water regularly during dry spells, especially from late July to September when flower buds are forming.





Nutrition: Light, sandy soils can be low in potash, making plants reluctant to flower. Apply superphosphate (70g per sq m/2oz per sq yd) and sulphate of potash (35g per sq m/1oz per sq yd) to such soils in spring.





Frost or bird damage: Flower buds may fall in spring during fluctuating day and night temperatures, and frost can damage flower racemes, leaving them wilted on the plant. Birds sometimes damage buds whilst searching for insects, but usually a few buds escape damage to provide some display.





Further information


Search the online RHS Plant Finder for suppliers of wisterias

How do you prune a Wisteria tree?
Pruning Wisteria: Cut back current year's side growths to about 6 ins. in July or after flowing.
Reply:A few basic pruning cuts will help you rejuvenate and control the size of your shrubs and trees.

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