Types of Invasive Plants You Should Avoid

Oriental Bittersweets

Bittersweets look desirable, but their appearance in your garden can be “bittersweet.” Distinguish between the three bittersweet types: oriental bittersweet (Celastrus orbiculatus), American bittersweet (Celastrus scandens), and bittersweet nightshade (Solanum dulcamara).

The Oriental bittersweet vine is the one that makes most lists of the worst invasive plants in North America. The other forms can also be invasive, but they are less so than Oriental bittersweet, which can take over your woodland garden. American bittersweet is the form with attractive red and orange berries often used in decorative displays.1

Chinese Wisteria

Similar to bittersweet, wisteria has several types. North American growers must determine whether they are growing American wisteria vines (Wisteria frutescens) or Chinese wisteria (Wisteria sinensis var.). Both types are robust growers, but Chinese wisteria poses a genuine threat south of USDA hardiness zone 4.2

English Ivy

If you wish to crowd out weeds in an area of your landscape, English ivy (Hedera helix) is a vigorous, attractive ground cover that tolerates shade.3 However, the problem is that English ivy grows well in most places and is too vigorous, earning it a spot on the list of worst invasive plants. It readily escapes landscape cultivation and is considered a seriously problematic invasive plant, especially in the Pacific Northwest.

Sweet Autumn Clematis

Sweet autumn clematis (Clematis terniflora) is another “good-looking” specimen that can overwhelm a landscape. It is especially problematic in the East and lower Midwest.4 This plant has a very sweet scent, but that’s the only pleasant thing. Another variety from New Zealand, Clematis paniculata, is sometimes sold as sweet autumn clematis, but this is a less invasive alternative.

Bugleweed or Ajuga

The mat-forming ajuga (Ajuga reptans), or bugleweed, is another popular ground cover that can turn thuggish. Because ajuga has pleasing purple blossoms and can suppress weeds, it is often planted in shady areas as a ground cover. However, ajuga can take over a garden or lawn and is especially problematic in warmer climates with no winter frost to kill the plants annually.

Barberry

Two types of barberry shrubs have assaulted North America: Japanese barberry Berberis thunbergii, from the Far East, and Berberis vulgaris, from Europe. These invaders come armed to the teeth, bristling with thorns, making them an effective hedge plant. Unfortunately, many of these barberry plants are so invasive that much of the Midwest has placed them on a list of dangerously invasive plants, strongly suggesting that they should never be planted.

Burning Bush

In autumn, burning bush (Euonymus alatus) puts on a show for the ages, bearing red or pinkish-red leaves. Colorful reddish-orange berries accompany the striking foliage. This exotic plant from Asia is beautiful but is considered dangerously invasive across much of the northern United States, from Maine to Minnesota and the Southeast.

Lantana

Lantana (Lantana camara) is a broadleaf evergreen shrub native to tropical areas. It is a notable invasive in Florida, Georgia, and across the South, going west to California. However, this pretty plant poses no danger in colder climates north of zone 9, where it is often used in hanging baskets. This plant can easily escape gardens and naturalize in dangerous profusion in warmer zones.

Butterfly Bush

Butterfly bush (Buddleja spp.) is among the worst invasives in the Pacific Northwest, where growing conditions resemble its native habitat. It is also an invasive problem in areas of the Southeast. It is less problematic in areas colder than zone 6 since the plant dies back to the ground each winter.

Butterfly bush is so-named because it attracts butterflies (as well as other pollinators), but to humans, the plant is somewhat unpleasant in odor. Consider growing butterfly weed (Asclepias tuberosa) as an alternative for attracting butterflies.

Common Privet

As with barberry, a privet hedge (Ligustrum vulgare) is common. But just because it’s popular doesn’t mean it isn’t a problem. This species is listed on the official lists of problematic plants in much of the Midwest and Northeast, from Pennsylvania to Maine. Privet responds well to pruning and tolerates the pollution that typically plagues plants in urban settings. Privet shrubs grow so fast that they can easily escape the boundaries of cultivation and become naturalized in the wild.

Norway Maple Tree

Full-sized trees can be invasive, too, as in Norway maple (Acer platanoides), which is considered invasive in much of the Northeast and dangerously so in Maine, Vermont, New Hampshire, and Massachusetts.5 Originally planted as a landscape species, its seeds easily disperse on the wind to naturalize in other environments.

Japanese Knotweed

Japanese knotweed (Fallopia japonica) is a clumping perennial plant with virtually no redeeming landscape value. The best thing to be said for its appearance is that it produces a fluffy-looking flower in early autumn (thus one of its alternate common names, “fleece flower”). Most everyone agrees to remove it on sight. It is an easy pick as one of the worst plants, considered invasive in every state, though worst in its natural hardiness zones, from 5 to 9.

Kudzu

Kudzu is an Asian perennial vine and one of the worst invasives ever. It is sometimes ruefully called “the vine that ate the South.” Kudzu is part of the pea family and is used as livestock feed, but it is an enormous problem in all Southern states.

Initially planted to shade porches on southern plantations, the plant quickly spread to surrounding territory, where it now gobbles up nearly all it touches. It grows well in sun and shade and is dangerously invasive throughout the South, Southeast, and the Atlantic seaboard.

One recent control effort is to let goats loose in areas infested with kudzu so they can eat their fill and rid the area of the kudzu.

Tansy

Tansy is an herb—and a toxic one with a rich tradition of medicinal and culinary use.6 But there’s more to worry about than its toxicity: Tansy plants are invasives that spread via seeds and rhizomatous roots, taking over swaths of land if left unchecked.

Purple Loosestrife

Purple loosestrife is thought to have arrived in North America as seeds in soil used as ballast in sailing ships in the early 19th century. Today, it is found in every state in the United States except Hawaii and Alaska.

Purple loosestrife invades wetlands, forming dense root mats that choke out native plants and degrade wildlife habitat. It looks beautiful when massed together, which is the norm since it spreads incredibly vigorously.

This problem plant is such a danger to the ecosystem that since 1992, the governments of Canada and the United States have introduced European beetles, Galerucella calmariensis and G. pusilla, to get rid of the plant—an experiment that seems to be helping curb the species.

Japanese Honeysuckle

Japanese honeysuckle (Lonicera japonica) is another attractive, sweet-smelling specimen that turns out to be a sinister foe.7 This vigorous, fast-growing twining vine has fragrant yellow flowers that appear from June to October and grow to 30 feet. When planted deliberately, it is used as a ground cover, but it is considered an exotic invasive across the entire Midwest.

If planted in the garden, great care should be taken to keep the plant in check, including aggressively cutting it back regularly. This plant can break tree limbs with its heavy weight and kill shrubs and trees by girdling them with vigorous vines.