Plant Doctor Archive

Waning wisteria

I PLANTED a wisteria about 18 months ago. The first spring it flowered on the old wood. I let it grow for the summer to fill the framework. I cut back some of the old wood in summer and again in winter to get the spurs, which I thought would flower. Unfortunately, this time it has failed to flower at all, even on the old woody spurs that flowered last year and were untouched. It is in a sunny spot and we get frosty winters so I am perplexed. Has it put all its energy into growing or is the soil too rich?

THE older a wisteria gets, the better it will flower. However, you may experience the odd hiccup in flowering for the first two or three years. But judicious pruning can improve things and, in later years, may be essential to control wisteria's sometimes rampant growth. In summer, around December, cut back all new season's growth to within three leaves of the main leaders (the old woody growth). This might seem drastic, especially when you're effectively cutting off as much as 75% of the leaf coverage. But the stubs you leave will form the flower buds for next year's display. A couple of months later cut back the next lot of new growth in the same way. Then in late winter do the same to any remaining long shoots back and remove any broken, weak or damaged pieces. If you stick to this system you should get great annual flowering and your wisteria shouldn't get out of hand.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.