Culture
Best grown in acidic, moderately fertile, medium moisture, well-drained soils in full sun. Best flowering in full sun. Periods of drought in summer and fall could cause flower buds to abort and not bloom next spring. Needs a sturdy support structure on which to grow. Can be invasive (rampant growth plus rooting surface runners and seedlings). Needs regular pruning to control size and shape of plant. Best pruned in mid-summer and again during winter dormancy to control vegetative growth and promote flower bud formation. Can be slow to establish. Grafted plants or cuttings of mature stems may take 2-5 years to bloom after planting, while seed grown plants may take 10-20+ years to bloom. Poor blooming performance is still a possibility even in ideal growing conditions and with proper pruning due to fluctuations in winter temperatures (a relatively warm period followed by freezing temperatures) or spring frosts/freezes.
Noteworthy Characteristics
Wisteria floribunda, commonly called Japanese wisteria, is a woody, clockwise-twining, deciduous vine endemic to woodland edges, thickets, streambanks and lake sides in Japan from northern Honshu south. It is widely cultivated as an ornamental around the world and has escaped cultivation and is considered invasive in parts of the eastern and southern United States. Mature vines typically grows 10-25' tall (sometimes larger). Can also be trained as a multi-stemmed shrub, small tree, or bonsai. Features bright green, 12-16" long, compound pinnate leaves (each with 15-19 leaflets) and 1.5-3' long drooping clusters (racemes) of fragrant, pea-like, blue to violet, pink or white flowers which bloom from the base of each cluster to the tip in May as the leaves emerge. Flowers give way to pendant, velvety, bean-like seed pods (to 6" long) which ripen in autumn and may persist into winter.
Genus name honors Caspar Wistar (1761-1818), professor of anatomy at the University of Pennsylvania.
The specific epithet floribunda means "free-flowering" or "producing abundant flowers".
'Rosea' has pale rose-pink-tipped-purple flowers.
Problems
This plant is considered invasive in parts of the eastern and southern United States. Though susceptible to a number of foliage-chewing insects and fungal diseases, none are significant. Considered a high maintenance plant, however, because of its need for regular pruning, its invasive tendencies which must be constantly monitored (particularly if grown on structures adjacent to buildings) and its vulnerability to late spring frost damage to flower buds.
Uses
Excellent vine for large, sturdy, free-standing arbors, pergolas or fences. Can be grown up the side of buildings on large trellises or other structures. May be trained as a specimen shrub or tree.