Regional Gardening Reports :: National Gardening Association

In the Garden:
February, 2005
Regional Report

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Thunbergia alata has escaped from gardens and naturalized in many tropical areas, including the islands of Hawaii. An annual for me, it blooms but hasn't self-seeded ... yet.

Good Plants Gone Wild

Runaway weeds, garden escapees, invasive exotics ... hardcore plants in the wrong place? There is some debate about what constitutes a truly invasive alien or exotic plant. We would all probably agree that to be categorized as "bad," a plant should be aggressively spreading and non-native to this continent, meaning it has been imported at some point in history.

But for me, an undesirable invasive could conceivably be a plant that is imported from another region and naturalizing locally to expand its range, or a plant -- native or not -- that colonizes rapidly in the garden and becomes an out-of-control thug.

Generally speaking, experts are most concerned about plants that are not native to North America but are spreading throughout natural areas and displacing plants that are truly native. This disrupts all kinds of natural processes and cycles.

But there are degrees of insurgence here. For instance, how scary is the plant that manages to spread its seeds on the wind, slowly expanding its territory year by year? Or the plant assisted in its spread by birds and animals, its track expanded literally across the map by how far the proverbial crow flies? Is its territory defined by where gardeners have planted it and unwittingly facilitated its march across the land? And is it invasive if nobody reports it? When I look at the maps documenting invasive plants, I often see the state of West Virginia oddly devoid of incursions and yet surrounded by severely invaded territory.

Plants That Make the Hit List
What "garden type" plants are we talking about? An odd selection, to be sure. I grew up thinking of multiflora rose as a flowering hedge plant, silver maple a wonderful fast-growing shade tree for a new suburban neighborhood, and butterfly bush a fabulous butterfly magnet. To me, chicory and Queen Anne's lace, and Japanese honeysuckle were cheery wildflowers, not invasive plants or imported exotics or garden escapees; and I certainly never thought of them as dangerous. (Except for the rose's thorns!)

But in today's world of raised consciousness, these plants could be considered all of those things, creating a thorny problem. In fact, today these and too many more (such as that infamous, seductively gorgeous scourge, pink lythrum or purple loosestrife) are widely labeled as bad plants, some are even ranked in the official category of noxious weed and thus belong among the lowest of the low.

And yet these lists may differ from state to state, sometimes county to county. In my home state, you would most likely recognize with ease the fragrant pale-flowered honeysuckle, the pink spires of lythrum and the sprays of tiny white multiflora rose followed by tiny hips that look like redhot cinnamon candies -- noxious every one of them. New to the list of worrisome plants is barberry, and in some areas burning bush has made the grade and fallen off the edge into bad plant-dom. Miscanthus, one of our favorite ornamental grasses for well over a decade, has also made the grade (or would that be failed the grade) in some areas.

This is a complex issue because many of these plants were broadly recommended in the gardening literature at one time, have been widely planted over the years, and are still widely available through both catalogs and often though our local nurseries. These plants persist in popularity precisely because they have iron-clad constitutions, thrive even in adverse locations, require little or no care, and offer great ornamental appeal. Some, such as the now notorious autumn olive, are overwhelmingly attractive to wildlife as well.

Gardeners Can Help
There are some practical steps you can take. If you already have some of these in your garden, keeping the plants deadheaded (where possible) can help slow their spread. Being aware of which plants are potential problems can help us know to seek out sterile cultivars or opt to substitute a different plant altogether.

Sometimes we can identify a plant that is native to the local area that could easily serve the same ornamental purpose without endangering nearby habitats. The least we can do is educate ourselves and make thoughtful choices.

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