The Pilgrims were not the only foreign settlers to come over on the Mayflower. The first exotic plants also ventured to the New World with early European visitors. Today as much as one-third of the plants in North America are exotic (and up to 80 percent of garden plants). Though many behave nicely in our landscape, some non-natives are considered “invasive,” with aggressive growing habits that choke out indigenous plants and pose a threat to native eco-systems.
Gardeners nationwide are joining a growing movement to stamp out the most harmful foreign invaders, but even the most conscientious may be surprised to learn that many of their garden favorites are in fact invasive plants. To help, we’ve compiled a list of the top 10 offenders and the best substitutes:
1. Invasive Plant: Butterfly Bush
Butterflies are not only pretty, these pollinators are also great for the environment. Unfortunately butterfly bush (Buddleia davidii) is not. A native from Asia, this plant is listed as an invasive in more than 20 states including much of the West Coast and the area east of the Mississippi. Though mature butterflies love this shrub’s sweet nectar, the butterfly bush provides no support for butterfly and moth caterpillars. More important, it threatens native species that do.
Native Plant: California Lilac
Above: California Lilac by Michelle Slatalla. For more, see Garden Visit: SF Botanical Garden in Golden Gate Park.
Gardeners who want to support the entire butterfly life cycle and still enjoy brilliant flower clusters should consider native alternatives such as California lilac (Ceanothus), and meadowsweet (Spiraea spp). Wild hydrangea (aborescens), viburnum, and azaleas are also good substitutes. The New England Wildflower Society has a list of more than a dozen native substitutes.
2. Invasive Plant: Japanese Honeysuckle
Above: Japanese honeysuckle (Lonicera Japonica) via Wikimedia Commons.
An aggressive, vine, Japanese honeysuckle spreads quickly over trees and along the understory, where it chokes out native seedlings.
Native Plant: Trumpet Honeysuckle
People are usually attracted to Japanese honeysuckle not for the brilliance of its blooms, but for their strong fragrance. Those who want a similarly sweetly scented vine should consider natives such as Trumpet honeysuckle (Lonicera sempervirens), Carolina jasmine (Gelsemium sempervirens), or leather flower (Clematis viorna).
3. Invasive: Purple Loosestrife
Swaths of Purple loosestrife (Lythrum salicaria) in a marsh may look dramatic and pretty, but this aquatic invader is choking wetlands in nearly every state in America.
Native Plant: Gayfeather
Gardeners seeking a similar, long-lasting, purple bloom should opt for Gayfeather (Liatris spicata), Grass-Leaved Blazing Star (Liatris pilosa), or purple coneflower (Echinacea purpurea.)
4. Invasive: Scotch Broom
Scotch broom (along with Spanish and French broom) is invasive in much of this country’s two coasts. According to Washington State’s Invasive Species Council, this European import and member of the pea family “forms dense, impenetrable stands” in open areas where it not only threatens native eco-systems, but also “slows reforestation and creates fire hazards.” People visiting areas with Scotch broom should wash their cars and boots to prevent spreading.
Native Plant: Mormon Tea
Native to the Southwest, Mormon Tea (Ephedra) is, like Scotch broom, ideal for dry, sunny climates with poor or sandy soil (read: deserts and shores). It also produces similarly bright yellow flowers with pollen used for medicinal purposes.
5. Invasive Plant: Rugosa Rose
The is a reason Rosa rugosa is so popular with coastal gardeners. It actually thrives in challenging growing conditions! Unfortunately, it does too well. This leafy shrub shades other native dune plants, mosses, and lichens upon which native fauna depend. Not only a problem in the US, this aggressive rose also threatens coastal habitats in Europe.
Native Plant: Virginia Rose
Above: Virginia rose by Stephen Horvath via Flickr.
A native of eastern North America, Rosa Virginiana also thrives in sandy, salty environments. Its blooms are much like those of Rosa rugosa and, in autumn, Virginia Rose, or Common Wild Rose, produces similar brilliant orange rose hips that provide food for local fauna. Unlike Rosa rugosa, the leaves of Virginia rose also support many beneficial insects and pollinators.
Another good native alternative, Carolina Rose sports similarly fragrant blooms and beneficial rose hips.
6. Invasive Plant: Japanese and Chinese Wisteria
For more about wisteria, see Wisteria: A Dangerous Beauty (Are You Tempted?).
Prized for its romantic, draping blooms, invasive wisteria was introduced by horticultural enthusiasts. Today escapees from the garden are invading American forests in “19 States, from Massachusetts to Illinois, South to Texas and also in Hawaii,” according to the Plant Conservation Alliance. In these regions, it threatens native woodlands, entwining and choking mature trees and shading saplings in the understory.
Native Plant: American or Kentucky Wisteria
Above: Above: Photograph by Nicole Franzen for Gardenista. For more of this Brooklyn garden, see The Magicians: An English Professor and a Novelist Conjure a Garden.
American Wisteria has only slightly smaller blooms, and is much less aggressive than its Asian counterparts.
7. Invasive Plant: English Ivy
With apologies to Harvard and the other “Ivies,” your signature plant is invasive in this country. When this vigorous vine escapes the confines of academia, it can entwine and choke trees and spread like a blanket over the forest understory. In urban areas it also harbors other unsavories such as rats and carpenter ants.
Native Plant: Crossvine
Ivy substitutes can be broken down in terms of what you want your ivy to do. Seeking a fast climber? Try crossvine, or native honeysuckle. Need a quick ground cover? Try Allegheny spurge (Pachysandra procumbens) or Green-and-gold (Chrysogonum virginianum). Evergreen? Shade plant? For many more suggestions, see The Virginia Native Plant Society’s comprehensive paper on Native Alernatives to English Ivy.
8. Invasive Plant: Japanese Barberry
Above: Japanese barberry by Kate Ter Haar via Flickr.
According to Eat the Invaders’ historic timeline, in 1875 The Arnold Arboretum near Boston received the first Japanese barberry plant, which was supposed to replace European barberry (a Colonial food source), which was discovered to harbor wheat rust. Today this invasive threatens native plants in much of the eastern and midwestern US.
Native Plant: Beautyberry
Above: Beautyberry by Eric Hunt via Wikimedia Commons.
If brilliant fall berries are what you’re looking for, try Beautyberry (Callicarpa americana), which sports purple berries that are as rare as they are charming.
9. Invasive Plant: Japanese Spirea
Above: Spirea Japonica by Paul Hermans via Wikimedia Commons.
Common in much of the Northeast, Southeast and Midwest, Japanese spirea or Japanese meadowsweet overshadows native herbs and shrubs.
Native Plant: Douglas Spirea
Above: Spiraea douglasii (Douglas Spirea) photo via Oak Point Nursery.
Fortunately, if you like the delicate pink blooms, there are many native substitutes with either flat or pointed flower clusters. These include: Ceanothus americanus (New Jersey tea), Leiophyllum buxifolium (sand myrtle), Spiraea douglasii (Douglas spirea), Spiraea spendens (mountain spirea), and Spiraea tomentosa (steeplebush).
10. Invasive Plant: Burning Bush
Birds just love the fruit of burning bush (Euonymus alatus), which means it will spread to wild environments rapidly. Currently, burning bush is considered invasive in most states east of the Mississippi where it threatens native forests, fields and coastal scrublands.
Native Plant: Chokecherry
If autumn color in the form of scarlet leaves and bird-friendly berries is your goal, try chokecherry (Aronia spp.). Mountain serviceberry (Amelanchier bartramii) also has nice autumnal foliage and fruit.
- USDA’s National Invasive Species Information Center.
- The New England Wild Flower Society’s Picks.
- National Park Service Plant Conservation Alliance.
- Early Detection and Distribution Mapping System.
- The United States National Arborteum.
N.B. A helpful reader also turned us on to The Xerces Society for Invertebrate Conservation. The site offers extensive lists of native pollinators by region and provides information on other resources for Canada and other areas around the world.