Wisteria

(Fabaceae [also known as Leguminosae] - Pea Family)

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• Form
  • medium-sized climbing woody vine
  • maturing at 30' long or more, depending upon cultural pruning and the size of its supportive structure
  • upright twining vine growth habit
  • very rapid growth rate (once established)

• Culture
  • full sun to partial shade
  • performs best in full sun, in climates with abundant heat and high humidity, in moist, well-drained, deep soils of average fertility, but is adaptable to poor soils, soils of various pH, and drought
  • propagated by rooted stem cuttings or seeds, with cultivars either grafted onto seedling rootstock or progated from rooted stem cuttings
  • Pea Family, with several minor disease and pest problems that usually are of no serious consequence
  • moderately available as a staked vine in containers
  • often slow to establish during its first one to two years of growth, but grows very rapidly thereafter (up to ten feet per year under optimum conditions, and sometimes more if pruned back hard on an annual basis)
  • many horticultural practices have been attempted to induce flowering at a younger age or to promote heavier flowering at maturity, often with limited or no success; the best recommendations seem to be the following:
    • purchase named cultivars, to ensure abundant flowering at maturity
    • do not expect flowering for at least five and possibly ten years after transplanting
    • place in a site that receives full sun all day, at a trellis or other supportive structure that will last for at least two decades (e.g., if untreated wood is used and collapses after ten years, severe pruning of the vine to allow for recontruction, and retraining of its new growth onto the new structure, will result in the temporary loss of flowering for at least two years)
    • place in a soil that is well-drained but of average fertility, to promote reproductive growth at the earliest possible age, rather than continued vegetative growth
    • fertilize once per year, either after frost or in early Spring, with a fertilizer that is relatively low in nitrogen and relatively high in phospate
    • once the plant is established (generally at about five years of age), prune back hard on an annual basis, either after frost or in late Winter/early Spring, leaving the short lateral shoots which (may) produce the inflorescences

• Foliage
  • bronzed new foliage rapidly becomes medium green, composed of odd-pinnately compound leaves that are alternate along the stems
  • leaves are about 1' long and have about 15 leaflets per leaf, with the leaflets being ovate, acuminate, and about 2" long each
  • fall color is poor, being light green or chartreuse at abscission

• Flowers
  • shades of blue, purple, violet, red-violet, lavender, or white, depending upon species and cultivar
  • mid-May, 8" to 15" long pendulous inflorescences occur before, during, or after foliage emergence (but before foliage is fully expanded), are extremely fragrant, are either sparsely to densely laden (depending upon vine maturity and cultural pruning), and are quite showy on mature vines
  • does not flower heavily (if at all) on young vines, or on mature vines that have been overfertilized with high nitrogen or are in high fertility soils
  • flowering occurs on the short lateral shoots, primarily from the previous season's growth (i.e., old wood), but occasionally from the new growth as well

• Fruits
  • 5" long pods are noticeable but ornamentally insignificant
  • pods are light green becoming brown, with each yielding a few seeds

• Twigs
  • twining stems are light green, becoming light brown at maturity and twisting around their supportive structure as well as around themselves
  • stems during the current season's growth are virtually unbranched, often growing from two to ten feet during the growing season without lateral bud break, unless pruned or sheared
  • leaves are often small at the curling stem termini during the rapid growth period of Spring and occasional growth flushes during Summer
  • terminal twig dieback from the most rapidly growing sections of the vine often occurs during Winter, which is normal and does not affect growth for the following season, or flowering from the short lateral shoots

• Trunk
  • single-trunked and branching very low, light brown to light gray, either remaining smooth or becoming muscled with age, often twisting upon itself or other adjoining branches, to the point of self-girdling or self-fusing
  • the vine can be pruned and supported at an early age into tree-form status, but this requires much annual maintenance to keep an attractive and semi-formal appearance

• ID Summary
  • woody vine with wispy stem termini, pinnately compound leaves, vigorous growth that is relatively unbranched within the current season's growth, and with pendulous Spring inflorescences (often blue-purple) that are very showy and very fragrant

• Function
  • climbing woody vine used extensively in the Southern United States and in Japanese gardens, supported by a trellis, fence, arbor, or tree (or alternatively allowed to trail over a rock fence or stone wall), and prized for its large, pendulous, showy, and extremely fragrant Spring inflorescences

• Texture
  • medium texture in foliage and bold texture when bare
  • thick density in foliage and medium density when bare

• Assets
  • extremely fragrant Spring flowers (often in full bloom before the foliage has emerged to a significant degree)
  • the large, showy, and very pendulous nature of the inflorescences creates an architectural "reverse vertical" effect of long hanging inflorescences
  • vigorously and rapidly growing vine (once established)

• Liabilities
  • often does not flower until five to ten years after being transplanted
  • the extremely vigorous and aggressive new growth on established vines may need to be pruned back at least once a year, for containment in restricted growth areas or to maintain some degree of formality
  • the twining and heavy foliage-laden branches can actually strangle and weight down trees or large shrubs if the latter are used as supportive structures
  • poor fall color
  • dieback of the wispy terminal stems in most Winters (creating a slightly unkempt appearance in early Spring if left unpruned, until the new growth consumes them)

• Habitat
  • zones 4 (or 5) to 9, performing much better in hot and humid climates
  • native to Japan, China, or the United States, depending upon species

• Alternates
  • perennial vines with showy inflorescences (Campsis radicans, Clematis, Hydrangea anomala petiolaris, etc.)
  • perennial vines that, when mature, cast a dense shade under supportive structures (Actinidia, Akebia quinata, Aristolochia durior, Parthenocissus quinquefolia, Parthenocissus tricuspidata, Vitis, etc.)

• Variants
  • the two common landscape Wisteria are noted below:
  • Wisteria floribunda - Japanese Wisteria - flowers open over several days from the base to apex of each inflorescence (remember that the apex is nearest to the ground on the hanging infloresences), stems twine clockwise (i.e., from bottom left to upper right on a cane pole), zone 4 hardiness, with many cultivars of various floral color and inflorescence length (from 1' to 3')
  • Wisteria sinensis - Chinese Wisteria - flowers open at about the same time along the inflorescence, stems twine counter-clockwise, zone 5 hardiness, with few cultivars

• Translation
  • Wisteria is named after Caspar Wistar, an 18th century American professor of anatomy.
  • floribunda translates as "abundant flowering".
  • sinensis translates as "from China".

• Purpose
  • Wisteria is a fragrant-flowering vine that is useful for draping over large supportive structures.

• Summary
  • Wisteria is known as an architecturally useful, showy woody vine that is cherished for its extremely fragrant, pendulous Spring blossoms that are often blue-purple in color.