Why Won’t My Wisteria Bloom?
Good question. It seems that while many people would like to have a wisteria bonsai, they give up on them when they fail to bloom consistently. After all, it is a rather dull looking plant when not in flower. I’m sure there are many non-blooming wisteria currently being used as umbrella racks.
Wisteria bonsai fail to bloom for several primary reasons.
The first is age. They do need to be 7-10 years old before they will even think of blooming.
Secondly they need a LOT of water. Either putting them in a shallow pan of water in the summer, or be available for watering 3-5 times a day in the summer. DO NOT leave them soaking year round. I’ve had just as good if not better blooming with hand watering, but it does take watering consistency. (In Japan they have watering drones called apprentices, who can water in their sleep if necessary. If you don’t own a drone, and don’t wish to water 28 times a day yourself, it is perhaps best to use the shallow pan technique for the summer growing season.)
The third thing to promote consistent blooming is to be careful when and how much you’re fertilizing. Some find it is best to fertilize strongly after flowering (April/May) until about July, and then slack off. This thinking goes that flower buds will set better for next year, and you will restrain foliage growth over the summer with less fertilizer later on. I’ve been experimenting with fertilizing some in the springtime and have not seen any dampening of flowering at all. But I still do fertilize stronger after the first flush of flowering is over.
Fourthly, the wisteria will usually produce some tendril growth, which if encouraged may shift the plant into a vegetative growth habit and reduce flowering. It may help to cut back these tendrils in August to prevent too much growth, and to create flower buds. I say may because I’ve also seen wisteria bonsai throw out tendrils and still flower well.
After that, keep the darn things in the sun, with your conifers. Put up big fans to keep the clouds away. And then watch them bloom.
Some claims are made about keeping wisteria pot bound, and I used to believe that too but I’ve seen recently repotted bonsai bloom just as well. Might be something to consider though. Wisteria bonsai can be a bit ornery. Keep adjusting what you’re doing, have patience, and remember lots of sun, lots of water, age, and good fertilizing after blooming are going to help a lot.
Maybe I should have titled this one ‘Preventing the Umbrella Rack!’ —but that would have been only slightly better than last week’s overly ambiguous title.