How to prune wisteria

Q How do you prune wisteria?

A You probably have Wisteria macrostachys, also known as Kentucky wisteria. This lovely plant blooms quite reliably in the Twin Cities area, producing hanging clusters of lavender-blue flowers. Though fast-growing, it's not as vigorous, nor are its flowers as large and fragrant, as the popular Japanese wisteria that thrives in milder climates.

Here's how to prune wisteria:

• Once new growth is obvious in spring, prune back any stems that show signs of winter die-back.

• Wait until Kentucky wisteria finishes blooming to do any additional pruning.

• To encourage more blooming, shorten side branches so they extend no more than 36 inches from the main stem.

• Thin out some of the stems if growth is so dense that light won't penetrate well.

If you're growing Japanese wisteria and hoping that proper pruning will make it bloom, you'll be disappointed. Although the vines survive our winters quite readily, producing plenty of leaves, they rarely bloom.