Wisteria is a fairly vigorous shrub, it is important that at planting time the soil is enriched to enable good establishment. Regular feeding during the growing season with a balanced feed will aid root growth and this will help with the initiation of flower buds. It is imperative that the plant receives sufficient water during dry spells, and especially during the first year of establishment.
To encourage a wisteria to flower, pruning may be required. This can be achieved by pruning back the vigorous leafy summer shoots. This ensures that the plant’s energies are diverted into producing flower buds.
Flowering is also improved if the main stems are trained horizontally then vertically. The flower buds are produced on short spurs and the aim of pruning is to encourage those spurs to develop along the framework branches of an established plant.
The simplest method is to carry out a two stage pruning regime. In late summer, cut back the long growths and shorter, lateral growths to 15 cm. Stems may be left un-pruned if they are required to extend the framework. These should be trained in.
In mid winter cut back the summer pruned spur shoots to two or three buds. At the same time reduce to 15cm any long growths that developed after summer pruning.