Prune Amethyst Falls Wisteria in late winter only if necessary to shape the plant and remove undesirable growth. Trim lightly after the first flush of bloom to encourage branching and repeat blooms.

I only prune branches that are in the way. It breaks dormancy and blooms later then other varieties. I get a huge first flush and small flushes of blooms until frost.

Prune away. While it's not as agressive as the Chinese, it's still very aggressive. Here are pics of year 5 on mine. This is 3, count 'em 3 plants. It's also very adorable.

Here is a link that might be useful: Wisteria, Amethyst Falls