By Dr. Leonard Perry, Extension Professor
University of Vermont
The issue of native plants has been the subject of quite a few articles and seminars these past few years. The issue involves such questions as "What is a native plant?" And, "How far should a gardener go in planting natives to the exclusion of non-natives?" One related concern that comes up is that of invasive species--plants that aggressively spread into areas they are not wanted, such as goutweed by its roots, or the purple loosestrife by its seeds.
Invasive plants, once established, are hard if sometimes practically impossible to eliminate or eradicate. Often invasive plants crowd out other more desirable plants, or even change habitats, as in the case of purple loosestrife destroying wetlands.
As with many issues, there are people on both ends of the spectrum although most are in the middle. On the one extreme are those who believe all non-native plants should be removed and only natives planted instead. On the opposite end are individuals who feel that this is a non-issue, and that beauty rules—plant what looks nice, native or not. The definition of "native" is itself a hotly debated current issue in gardening.
Most of us would like to use at least some native species in our gardens so want to know more. It's important to remember that both natives and non-natives can have beneficial properties, such as attracting bees, butterflies, and hummingbirds, as well as serving as food sources for birds.
One definition of "native" refers to plants that originally were growing in this country when the first settlers arrived. A problem with this definition is that what may be native in Georgia or California may not be native here in New England, and may, in fact, become a weedy nuisance. Plant ecologist and owner of Prairie Nursery in Wisconsin, Neil Diboll, has addressed this problem by defining natives both in terms of location and time. He states that the problem "isn't point of origin but rather behavior."
This brings us back to the invasive issue. Some people argue that the problem with "exotics" or non-native plants is that they are invasive. But others make the point that so, too, are some of the native plants, such as goldenrod. Many, if not most, introduced or exotic plants in gardens behave quite nicely, so the argument is, why should gardeners discard them?
Are you aware that many of our wildflowers have been introduced and escaped to become "naturalized?" Some were brought over by early settlers for specific purposes, such as cattle feed or fiber. Others came in as seeds on shoes, boats, and luggage.
You also need to keep in mind that plants can be invasive either from spread of seeds or roots. Invasiveness is itself a function of location. Many plants listed as invasive don't behave this way in my zone 4 garden. They either don't get enough heat or long enough growing season to become a problem, or the season is too short for them to set seeds (such as with the Miscanthus grasses).
So what's all this mean to gardeners? To me, one key point is that not all natives are good and not all exotics are bad. It seems that a plant's "bad" behavior, or in other words, its aggressive or invasive habits, is what's not desired, and this can be found in natives and non-natives. Diversity in the landscape and the garden is what most gardeners really want. As Diboll states, "diversity is the ecologist's bias because to us diversity equals health in an ecosystem."
Janet Marinelli of the Brooklyn Botanic Garden is an author, editor, and champion of the gardener's role in the preservation of the planet. She feels that one day the native issue won't be an issue at all. "Someday," she believes, "we'll know enough about ecology to be able to create totally new plant communities, combining species from around the globe that add to, rather than subtract from, the planet's wonderful variety of life forms."
So it seems to me that a gardener's main concern, before planting any "new" plants in his or her garden, should be whether the plants will get out of control in that particular climate and spread through the surrounding natural landscape, especially to the detriment of other plants. As a rule, gardeners should be promoting diversity through their plant selections, rather than monocultures. By paying attention to invasiveness and diversity, and being so informed, gardeners will be able to garden more responsibly.
If you want to study the issue further, some good points were made in a recent article on the Brooklyn Botanic Garden Website (http:// www.bbg.org/), as well as in forum discussions on the GardenWeb Website (http://www.gardenweb.com)