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 these and other early European visitors. Today reports put the number of non-native flora in North America in the thousands—according to one source fully one-third of total plants, and up to 80 percent of plants in our gardens. Though many integrated quite nicely into our landscape, other non-natives are considered "invasive," which means their aggressive growing habits choke out indigenous plants, posing a threat to native eco-systems.
Gardeners nationwide are joining a growing movement to stamp out these foreign invaders, but even the most conscientious may be surprised to learn that many of their favorites are in fact invasive plants. To help, we've compiled a list of the top 10 offenders and the best substitutes:
1. Invasive: Butterfly Bush
Above: Butterfly bush (Buddleia davidii) photograph by Daniel Vucsko via Flickr.
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 Alternative: California Lilac
Above: California Lilac by Josh Jackson via Flickr.
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 team at Beautiful Wildlife Garden put together a comprehensive list of native, butterfly-friendly, alternatives by state and region. The New England Wildflower Society also has a list of more than a dozen native substitutes.
2. Invasive: 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 Alternative: Trumpet Honeysuckle
Above: Photograph of Trumpet honeysuckle (Lonicera sempervirens) by Janet Allen of Our Habit Garden, an excellent native plant resource for New York State.
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 leatherflower (Clematis viorna).
3. Invasive: Purple Loosestrife
Above: Purple loosestrife photogrpah via Natural Lands Trust, "a non-profit land conservation organization dedicated to protecting the forests, fields, streams, and wetlands that are essential to the sustainability of life in eastern Pennsylvania and southern New Jersey."
Swathes 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 Alternative: Gayfeather
Above: Gayfeather by D. Barronoss via Flickr.
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
Above: USDA photo of Scotch Broom via Controlling Scotch Broom by Gardening Know How.
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 Alternative: Mormon Tea
Above: Mormon Tea by R. J. Cox via Flickr.
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: Rugosa Rose
Above: Rosa rugosa by Claudia Daggett via Flickr.
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 Alternative: Virginia Rose
Above: Virginia rose by Stephen Horvath via Flickr.
A native to eastern North America, Rosa virginiana also thrives in sandy, salty environments. Its blooms are much like those of Rosa rugosa and, in autumn, Virginia or common wild rose produces similar brilliant orange rose hips to 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: Japanese and Chinese Wisteria
Above: 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 Alternative: 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: English Ivy
Above: English Ivy by Michael W. May via Flickr.
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 Alternative: Crossvine
Above: Crossvine by Susan E. Adams via Flickr. For more friendly climbers, see Alternatives to Ivy, Vertical Growers.
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: 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 Alternative: 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: 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 Alternative: 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: Burning Bush
Above: Photograph by John Lillis via Flickr.
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 Alternative: Chokecherry
Above: Photograph by Joe Calhoun via Flickr.
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.
Other sources:
- USDA's National Invasive Species Information Center.
- The New England Wild Flower Society's Picks.
- National Park Service Plant Conservation Alliance.
- The United States National Arborteum.
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