‘Blue Moon’ Wisteria is a popular ornamental plant, valued for its beautiful, fragrant, cascading flowers. While some wisteria species are known for their aggressive and invasive nature, many gardeners question if ‘Blue Moon’ shares these traits. Understanding its characteristics is important for informed planting decisions.
The Truth About Blue Moon Wisteria’s Invasiveness
‘Blue Moon’ Wisteria, scientifically known as Wisteria macrostachya ‘Blue Moon’ (also sometimes classified as Wisteria frutescens var. macrostachya ‘Blue Moon’), is a cultivar of a North American native species. Unlike the highly invasive Asian species, Chinese wisteria (Wisteria sinensis) and Japanese wisteria (Wisteria floribunda), ‘Blue Moon’ is generally not considered invasive in North America. Its native origin means it evolved within the North American ecosystem, making it less likely to outcompete and displace native flora.
The primary reason ‘Blue Moon’ is not invasive stems from its growth habits and reproductive characteristics. While vigorous, it has less aggressive root spread and produces fewer viable seeds than its Asian counterparts. Seeds from Asian wisteria species are dispersed by water, contributing to their spread in riparian areas, and they can also sprout repeatedly from root fragments. ‘Blue Moon’s less prolific seed production limits its ability to establish new populations.
Its growth rate is also less rampant than Chinese or Japanese wisteria, which can grow to immense sizes and smother existing vegetation. Invasive wisterias can girdle and kill trees by tightly twining around trunks and branches, altering forest ecosystems. Unlike invasive wisterias, ‘Blue Moon’ integrates harmoniously into the landscape, supporting local wildlife within its native range.
Distinguishing Blue Moon from Invasive Wisteria Species
Differentiating ‘Blue Moon’ Wisteria from its invasive Asian relatives, Wisteria sinensis and Wisteria floribunda, can prevent accidental planting of harmful species. One key distinction lies in their flowering times and characteristics. ‘Blue Moon’ blooms in late spring to early summer and can rebloom multiple times. Chinese wisteria typically blooms in early spring before leaves emerge, with all flowers on a raceme opening simultaneously. Japanese wisteria flowers appear after leaf expansion.
Another identifying feature is the appearance of their flower clusters, also known as racemes. ‘Blue Moon’ produces fragrant, pea-like, blue or lavender-blue flowers in racemes 6 to 12 inches long. Chinese wisteria has less fragrant, blue-violet flowers in racemes usually 6 to 12 inches long. Japanese wisteria boasts longer racemes, often 12 to 18 inches, with pink to purple flowers. The vines’ twining direction also differs: ‘Blue Moon’ and Chinese wisteria twine counter-clockwise, while Japanese wisteria vines twine clockwise.
Seed pod characteristics also vary. ‘Blue Moon’ produces velvet-like, bean-like seed pods 4 to 5 inches long that ripen in autumn. Asian wisteria species, particularly Japanese wisteria, produce numerous velvety brown seed pods 4 to 6 inches long that are noticeably hairy. Chinese wisteria pods are also velvety and bean-like. Observing these specific traits can help gardeners ensure they are cultivating the desired non-invasive ‘Blue Moon’ variety.
Managing Vigorous Growth
While ‘Blue Moon’ Wisteria is not invasive, it is a robust vine that benefits from regular management to maintain its form and promote flowering. It can reach heights of 15 to 25 feet and requires a sturdy support structure, such as a pergola or arbor. Proper pruning is essential for controlling its size, shaping the plant, and encouraging prolific blooms.
Optimal pruning times for ‘Blue Moon’ Wisteria involve a two-stage approach. A dormant season prune, usually in late winter or early spring before new growth begins, involves cutting back last year’s growth to a few buds to encourage flower production. Summer pruning, performed after the first flush of blooms, shortens long, new vegetative shoots to about 6 inches, encouraging reblooming. This directs the plant’s energy towards flower development. Training the vine on its support structure by tying stems as they grow is also important to guide its habit and prevent it from becoming a tangled mass.
Ecological Considerations and Responsible Planting
Choosing ‘Blue Moon’ Wisteria, a North American native cultivar, aligns with responsible gardening practices that support local ecosystems. Native plants are adapted to regional climates and soils, meaning they generally require less water and fewer fertilizers once established. This reduces the need for external resources and can promote a sustainable garden environment.
Native wisteria varieties benefit local wildlife, serving as a food source and habitat. Their flowers provide nectar for native bees, butterflies, and hummingbirds, contributing to garden biodiversity. Selecting ‘Blue Moon’ over its invasive Asian relatives helps prevent the spread of species that disrupt natural plant communities and outcompete native flora. Making informed choices about plant selection is a meaningful step toward fostering a balanced and thriving local ecosystem.