Wisteria is one of the most splendid deciduous vines any gardener can grow, but it can be frustrating when the plant doesn't bloom. There are a few things you need to know about selecting a wisteria and a few more tips for growing one that will enhance your yard. Once you get the hang of it, you, too, can have those twisted, gnarled stems, overarching leaves and pendant blossoms that make up the romantic and nostalgic vision of a wisteria vine.
First, there are two main types of wisterias available at the nursery--the Japanese wisteria (W. floribunda) and the Chinese one (W. sinensis), which is most commonly grown in the Pacific Northwest. The biggest difference between the two is the flower--Japanese wisteria has longer sprays of pink or lavender blossoms that open gradually over a period of weeks while the Chinese form has a multitude of violet-blue flowers that open in one big splash in spring. Each type is available in different cultivars of differing colors (white, pink and lavender or purple). I have the classic lavender one that covers an arbor and spills its inflorescence over a rustic bench each May. It's breathtaking.
Whichever you select, all of these vines have some things in common. Once established, they grow rampantly! They need support, even when they are grown as umbrella-shaped topiary. You can grow it in a whisky barrel or other large container if you must.
Every wisteria needs regular hard pruning both to keep the plant from overwhelming everything in the neighborhood and also to promote good blossoming. Those whippy branches can grow a dozen feet or more in one season. They can pry shingles off your house or roof. Mine is competing with a laurel hedge and a large vine maple. So far, the wisteria is winning. Plant your vine near a very sturdy trellis or arbor. Just make certain that it has something hefty to lean on that won't pull apart or fall down. Many commercial trellises are simply too flimsy to suit this plant.
Wisterias with lots of leaves but few blooms are a common complaint--and why have it if it won't perform? The problem can be that the plant was raised from seed--no flowers there for many, many years--so always get a vegetatively propagated plant. Either own-root cuttings or grafted plants will work.
A second reason for scant bloom is too little sun. Like most Northwest gardeners, I have a lot of shade so I must prune back competing trees to open up that part of the garden and let the sunshine in. Wisteria wants sun and more sun. Don’t over-fertilize. Too much nitrogen (or even too much balanced fertilizer) can give you lots of leaves with no flowers.
Finally, unpruned plants may have scanty blooms so high you can't see them. Hone your secateurs and don't be afraid to use them. Timing of this pruning is not really critical--buds can be rubbed off a stem at any time and the main shoots can be cut back severely just after the bloom is finished. New buds form over summer for the following spring's show. If all else fails, try root pruning an older plant. This may shock it into blossom.
Wisterias like well-drained acid soil and, once established, don't need a lot of supplemental water in summer. They don't need fertilizers. They seem to resist pests very well. If you have yellowed leaves or signs of an insect, take a hefty sample to your local Master Gardener clinic for advice. But, in general, these are easy adaptable plants that live for years and years. I love to sit under mine and sip tea in the dappled shade. So soothing. So romantic. So easy.
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