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Selecting and growing wisteria demystified
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Most Midwestern gardeners regard wisteria as an exclusive southern charmer or as an impossibly frustrating northern challenge. The fact is, American or Kentucky wisteria (Wisteria frutescens syn. macrostycha) is a hardy northern plant that can provide delicious pleasure without waiting a lifetime for bloom.
Don’t be fooled--no wisteria is a “plant it and leave it” selection. Wisterias need maintenance in order to maximize bloom and prevent it from pulling down less than sturdy structures. But the American wisteria is can provide heavenly scent and beauteous bloom in June and a wonderful cover for a pergola or shade structure.
The better known wisterias are Chinese (W. sinensis) and Japanese (W. floribunda), and while Chinese wisteria can be hardy in Des Moines, both these Asian varieties bloom on buds set the previous season so knowledgeable pruning is essential. General recommendations are to prune back to 6 inches in the fall, prune to 3 buds per offshoot in late winter, and then pinch non-floral shoots during summer. One of the best explanations of how to discern floral shoots I’ve found is from Fine Gardening Magazine’s on-line resources . One way of discerning Chinese from Japanese wisteria is that the former winds counterclockwise around its support, while the latter winds clockwise.
Some gardeners have waited seven to 15 years for these species to mature and flower. On the other hand, American wisterias (e.g. ‘Amethyst Falls,’, ‘Aunt Dee,’ ‘Aunt Maude,') bloom on new growth, usually in June, and have been known to bloom in three years or even the first year after planting. While the blooms are smaller (7 to 12 inches) than the Asian varieties (Japanese wisteria can sport racemes of blooms from 8 to 20 inches in length!), W. frutescens is still extremely fragrant. Frequent light pruning during the summer will send energy to the roots and improve the late spring bloom.
Wisterias belong in the legume family (e.g. peas) and as such, fix their own nitrogen on root nodules, thus little additional fertilizer should be added. Too much nitrogen will simply encourage the plant to produce more foliage and little or no bloom. Regardless of what species of wisteria is used, make sure to provide supports adequate to handle the heavy and woody nature of this vine. Four-inch posts are often suggested with a minimum of 2 by 4 inch cross beams.
Some Des Moines area garden centers carry ‘Aunt Dee’ and others carry a blue Chinese wisteria. Call ahead or look on-line to find additional sources for these vines.
Important notes: The seeds of wisteria are poisonous. Also, new plants grown from seed may not have the same characterisitics as the original plant.
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