Wisteria: Growth is easy to control
My Wisteria Honbeni has been planted next to my house wall for three to four years. The problem is that it seems to grow approx a foot every week so needs constant pruning to keep in shape and in this time we have not had one flower. The plant is healthy an abundance of good glossy leaves and is approximately 15 feet tall. What are we doing wrong? (S Harris, Wisbech)
Wisteria are actually quite simple to prune – but it does need to be done correctly to keep the growth and size under control and improve the flowering display. Wisteria need pruning twice a year, in July or August, then again in January or February.
During the summer it is just a matter of controlling the whippy green shoots of the current year's growth to five or six leaves per shoot after flowering. This controls the size of the wisteria, preventing it getting into guttering and windows, and encourages it to form flower buds rather than green growth.
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Then, in winter cut back the same growths to two or three buds. This is best done in January or February to tidy it up before the growing season starts.
The ideal way to grow wisteria against a wall is to train it as an espalier, with horizontal support wires (3mm galvanised steel) set 30cm (1ft) apart.
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Over time, and with pruning twice a year, plants will build up a strong spur system.
Use new growths that develop near the base of plants as replacement shoots, if necessary, or cut out at their point of origin.
The most common problem gardeners have with wisteria is poor flowering. This can be caused by a number of things but the most common is time: young plants grown from seedlings can take 20 years to flower, so avoid disappointment by either buying a plant while it is in flower or choosing a named cultivar.
As a general rule always prune after flowering. Take care to water in dry spells between July and September, when flower buds are forming for next year, as drought at this time can result in failure to bloom Be aware that sharp spring frosts can damage developing flowers, causing them to drop before they open, or to distort.
Sometimes a mature and apparently healthy plant will suddenly die and be replaced by a new shoot growing from the ground.
•This article was first published on October 8, 2011.