Guide to Pruning Wisteria
There are three common types of Wisteria; Wisteria sinensis, Wisteria floribunda and Wisteria brachybotrys. W. sinensis has long flower stalks and flowers in May and June. W. floribunda has slender and the longest flower stalks among Wisteria, while W. brachybotrys has short flower stalk with larger scented flowers. Wisteria comes with white to bluish-violet to reddish-violet and pink hues depending on their varieties. Wisteria can be trained against walls as espaliers, up pergolas or as standards. Regular pruning is required in order to obtain a spectacular display and healthier plants. When pruning is not done, it can grow at approximately 4m a year, invading and damaging gutters, downpipes and roof tiles.
Prior to pruning, identify the two type of new buds, i.e. the floral (figure a) and vegetative bud (figures b, & c).
When to prune:
Summer pruning (July and August)
- After the plant has finished flowering
- Cut back whippy green shoots to five or six leaves on the main branch (figure c)
- Cut above a bud
Winter Pruning (January and February)
- When the plant is dormant and leafless
- Cut back the summer pruned growth to two or three buds
Formative and pruning espaliers:
- To cover a wall or fence.
- On the first year (winter), removed weak whippy stems and prune the strongest main stem to a bud 75-90 cm above ground.
- In summer, tie in the main shoot vertically, select two strongest side shoots and trained them at 45 degree. Remove any growth from the base.
- In the second year, cut back the main shoot in winter to 75-90 cm. Untie the side shoots and cut a third of their lengths.
- Train other side shoots in summer at 45 degree.
- After the third and subsequent year, cut back the main stem maintaining them at 75-90cm in winter, cut the upper side shoots by a third.
- Once the main stem had reached the desired height, remove the tip in the following February to encourage the formation of side shoots.
- Prune the side shoots the following winter by a third. Repeat the process until the head is formed.
Pruning neglected Wisteria:
- In winter, remove all damaged old and unwanted branches by cutting them back to a suitable branch.
- Alternatively, they can be cut out completely at their base.
- Hard renovation pruning will likely reduce flowering for a first few years.
- For best results, start feeding wisteria in early spring.
- Flower promoting fertiliser which are rich in potassium and magnesium in early March.
- In sandy soil, apply sulphate of potash at 20g/m2
- Avoid feeding after hard pruning.