Be On Guard Against Invasive Plants

The gardener's battle against weeds is continuous. We use many techniques to control them, yet they still invade our gardens and landscapes.

Plants that become "weedy" are very good competitors, and they move in with ease from nearby vacant lots, fence rows, fields, pastures, woodlands, and even our own or the neighbor's garden. The last source is of special concern. We can accept native plants that are weedy (they were here first), but what about the plants intentionally grown that become weeds in our gardens and move into the natural plant communities?

Our concept of what a weed is depends on our perspective. Bermudagrass serves as a good example. This is a welcome forage in a southern farm pasture and an excellent lawn and athletic turfgrass in warm areas. On the other hand, if it becomes established in a bluegrass lawn or spreads into a flower border, it suddenly becomes "wiregrass" and in need of rigorous control methods.

Now consider your own perspective if you saw bermudagrass spreading into a meadow of native grasses and wildflowers. Is it a weed here? Consider further the fact that bermudagrass was brought to this country from Asia. It is not a native grass, but is able to compete with and crowd out native plants. This has happened in many areas of the South and Southwest, and is a concern to many individuals involved in conservation efforts.

A great many of our garden and landscape plants have been imported from other parts of the world. In most cases, these plants are poor competitors and survive only with human assistance. However, other non-natives are more aggressive and can escape from cultivation. They spread rapidly where environmentally adapted because the native plants are not able to compete successfully. Most of us pay little attention to these imports as they naturalize in our wild areas, but in many areas they have become serious enough to threaten the stability of the native plant habitats.

Problems with these invasive plants are often the result of a good intention gone wrong. Bermudagrass is valuable when under control, but a terrible weed if it escapes.

Kudzu was introduced from the Orient as an ideal soil stabilizer to protect damaged soils in the South. But this plant can grow 50 feet in a season, smothering every other plant in its path, and is now referred to as the "green cancer" of the South.

Multiflora rose was brought from Japan and promoted for widespread planting as a "living fence" for pastures and an ideal food and shelter source for wildlife. A major control program is now being conducted against this rank-growing bush. T

he succulent garden weed, purslane, was brought from Europe as a vegetable greens crop. Ailanthus or Tree-of-Heaven, another import, is a tree very tolerant of poor soil and urban air, but now is naturalized and a persistent weed.

Other imported ornamental plants gone out of control in parts of the country include Oriental bittersweet, bamboo, morning-glory, Scotch broom, bracken fern, foxglove, pampas grass, and Japanese honeysuckle.

As with kudzu and multiflora rose, the problem of escaped plants can develop when only one aspect (for example, the benefits of soil stabilization or wildlife conservation) is considered, and not the entire environmental effect. Plant imports are now much more closely studied to avoid introducing potential problems, but many of the current problems will expand as invasive plants are carelessly grown.

Gardeners are called upon to take a personal role in controlling the spread of invasive plants. Even reputable garden companies will offer many of these plants, or government agencies will recommend them for particular purposes, presuming they will be maintained and controlled in the landscape. As new plants are being considered for the garden, check your references for warnings about heavy seed production, rank growth, or other weed characteristics. If the plant does pose a potential problem, avoid it or be prudent in keeping it under control, particularly if gardening an area near natural and un-maintained habitats.