Invasive Species

Lythrum salicaria in a colorful border

Lythrum salicaria in a colorful border

Back in the 1980s, it was almost impossible to pick up a gardening book or horticultural publication that didn’t recommend planting species that are banned or restricted today as invasive plants. Some states have extensive lists of banned or controlled species, while other state lists are more moderate. Sometimes the lists make no sense unless you understand the particular economics of a state’s agriculture. The bans or restrictions may be specifically to protect grazing cattle or cranberry bogs or even wildlife restoration. More often, the listed plants are so aggressive that native species are being crowded out.

 For example, picture books thirty years ago, extolling English perennial borders, included photos and planting plans for Lythrum salicaria. Even the popular book “Bold Romantic Gardens”, by Oehme and van Sweden, claimed that Lythrum salicaria  was not invasive. Today we know that there is no such thing as a non-invasive Lythrum. It’s too bad, really, that Lythrum is so invasive, because very few perennials come close to Lythrum’s unique color, and only Liatris spicata comes close to Lythrum’s spiky floral presence in the garden.

Among vines, the Chicago Botanic Garden’s publication from the 1980s, “Vines for Northern Gardens”, recommended Five-leaf Akebia (Akebia quinata), Porcelain Vine (Ampelopsis brevipedunculata), and Oriental and American Bittersweet (Celastrus orbiculatus and Celastrus scandens, respectively). In some cases, the accompanying description suggested that these vines were aggressive, or that seed spreading might be problematic, but none were banned from most state commerce at the time.

In the highly respected tome from The Garden Club of America, “Plants That Merit Attention, Volume I–Trees”, published in 1984, Phellodendron amurense (Amur or Chinese Cork Tree) is listed as a “handsome, tough, small shade tree”. To the credit of the authors, a final descriptive sentence suggests:  “A grafted male clone, with no pods to be removed, might be considered best for city planting.” As of 2015, the State of Wisconsin has banned the female tree entirely.

If you live in the United States, I encourage you not only to check your own state’s list of invasive species, but also to check out the lists of some other states. I think you may be surprised by some of the plants that are listed. Indiana, Illinois, Iowa, Delaware, Missouri, Maryland, Michigan, New Jersey, and Nebraska have especially fine websites for invasives. Not only do these state sites list the plants, and how to identify them, they also explain why the plant has been listed as posing a threat. When checking the lists, note that for many species with varietals, certain varieties are still acceptable for planting. The allowed varieties are usually seedless or nearly seedless.

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