Legend has it that a wisteria takes seven years to produce its wonderful racemes of fragrant purple/white flowers. Some wisteria do indeed reward their owners’ patience with a magnificent show after a very slow start. Less fortunate owners can get to the end of seven years – or indeed seventy – and still have nothing to show for it, other than an unrelenting mass of vegetation.
The majority of pruning requests we receive are from despairing clients who have either run out of hope at the prospect of ever seeing a flower, or who are intimidated by the sheer vigour of a plant that seems to be out of control.
Why is this plant so fickle in its flowering habit and what can you do to transfer the plant’s misplaced energy from producing whippy tendrils into a fantastic display of flowers?
The good news first
Coaxing a wisteria into flower is achievable for 99% of all the non-flowering plants we are asked to work on. But there are four vital techniques to get right: positioning, feeding, responding to any pests and diseases, and, of course, pruning.
Position: Wisteria needs sun to bloom – six hours a day as a minimum; if the wood of the previous year’s growth is exposed to the sun, this will ripen and help to form the flower buds for the following year. If you think your wisteria is in the wrong place, don’t hang about. Take action now with a spade; dig it out and move it to a sunnier spot.
Feeding: Before feeding, we always examine the plant and the soil to understand which nutrients the plant may be lacking. Wisteria are very specific in their feeding needs, and a small adjustment in certain micro nutrient levels will make a huge difference to their flowering power. Despite their ability to fix their own nitrogen, they are hungry feeders, so a mulch of compost in March, and a fertilizer that is high in potassium will keep the nutrients at the right level.
Pests and diseases can range from brown scale to honey fungus. Brown scale is the latest villain on the block. In 2011, it was all over London; in 2012 I saw it on two wisteria in Headington and Cowley. It tends to attack wisteria that are already weakened by drought from earlier years or lack of feeding.
Pruning: I would say this, but the real secret to encourage a flowering wisteria is pruning, especially in July. Continuous removal of the whippy tendrils from end of flowering onwards will always help. The January/February prune is also useful in removing any final summer growth that was left over from last year, and in allowing you to see clearly any structural changes that need to be made, now that the leaves are off.
Root pruning: In certain situations, a root prune is also required. This takes judgment and experience in knowing what to cut and when, and should only be resorted to when your other options have been exhausted. It does, however, yield some spectacular results.
And now for the bad news!
There is one situation in which a wisteria will never flower. You’ll see down at ground level a bump at the base of the wisteria. This is the place where the particular variety of wisteria you have chosen was grafted onto the rootstock. It is called the graft union. Sometimes, the graft doesn’t take, and the plant then reverts to the wild form that is produced from the rootstock. In this case, the plant may never produce flowers. If you buy your wisteria in May when it is in flower, you can be confident that the graft is fine. If, however, you find in future years that the wisteria has stopped flowering, then something has gone awry with the aftercare. This is a polite way of saying that the problem is you! Don’t take offence, but do follow the steps above, and your wisteria will be back in flower in no time.
Please feel free to contact us on 07887 371 656 if you would like us to help coax your non-flowering wisteria into flower, or if your wisteria is flourishing and is ready for a prune.
Oxford Pruning Company 
Leave a Reply