I know that pruning the wisteria helps promote its flowering and that the Chinese type (Wisteria sinensis) frequently has a summer rebloom but I hadn't really drawn the direct connection until today.

We have a Chinese wisteria that was planted in late summer 2000. We have been growing it as a tree/shrub so it has been heavily pruned from the begining. It had its first flower - in the summer - in 2002 and has flowered reliably in the summer every year since then. It has only bloomed twice in the spring (2006 and this spring) although it started showing buds in spring in 2004. May frosts took killed them most years. We lost about half of the buds this year but still got a good showing. All summer, as the long whippy new growths appear, we cut them back. Today, as I was admiring the new flowers and buds, I noticed that almost every group of new buds or flowers was happening at the site of where I had cut back those whippy growths. So I conclude that cutting the new growth is what prompts the summer bloom. And I think the more summer bloom you get, the more spring bloom is likely to happen too as there will be more 'flowering wood' on the tree.

Here is the sequence of events as I see them:

New 'whippy' growth in need of pruning (sorry for the fuzzy picture...):

{{gwi:252576}}

And here is what shows up about 10-14 days afterwards:

{{gwi:252577}}

Which blooms a few days later:

{{gwi:162551}}

Our wisteria tree/bush is now rather large and we'll be needing to do some more drastic pruning by next year (or maybe later this year). We are also trying to grow a two Henryi clematises through it for additional blooms. They're doing quite well so far (they were planted last summer) There's only one flower showing in this picture from this morning but there are more buds on the vines.

{{gwi:252578}}

The wisteria is considerably larger than it was the first time it bloomed in spring 2006:

{{gwi:199000}}
(It's really a blue color - the evening light did funny things to the color in that picture...)

It was late to bloom this spring, probably because of the cold, so the leaves were starting to emerge before it bloomed in early June this year. Even having lost about half its buds, it looked reasonably good:

{{gwi:252580}}

I've always thought prune, prune, prune was the way to get wisteria to flower well and now I'm convinced that there is a direct relationship between the summer pruning and flower production.