We have had a Wisteria sinensis (Chinese wisteria) for about 4 years. I have been shaping it into a umbrella-shaped tree and it has been growing well, but has failed to bloom for us. I read that I should cut the roots, so we have done that and still no blooms. It is located where it receives morning shade and then sun from noon on. Can you give me some ideas to try to make it bloom? Also what time of the year should it bloom?

Wisteria sinensis (Chinese wisteria), along with any other wisteria, may often prove difficult to flower. The tree and vine forms both require a site with full sun as well as a well-drained soil. Wisteria also need to be planted in a protected area as winter winds may kill off any flower buds. Little, if any, nitrogen fertilizers should be used since they promote leafy growth and inhibit flowering. Instead, use a fertilizer high in phosphorus. Heavy pruning should be done only in June, after normal flowering should have occurred. Very rarely does Chinese wisteria bloom on new growth, meaning a fall or winter pruning would remove potential buds for the next flowering season.

“Root pruning” is a technique used to stress the plant into producing a bloom. This technique is best done in May or June, after the flowering occurs. Use a sharply pointed shovel to make the slits, which should form a circle around the tree at a diameter of two feet for every inch of stem diameter. Be patient, as it sometimes takes two to three seasons for root pruning to be effective.

Another tip is to always purchase named cultivars, rather than seed-grown stock. The cultivars tend to produce better and more reliable blooms.