Wednesday, July 29, 2009

Alien Invaders in Your Yard!

Alien invaders are in our midst! They may not be blood-slurping killer carrots from outer space, but they are here all the same. In forests and meadows, wetlands and public parks, non-native invasive plants are on the march. Earthlings beware!

Each year, exotic invasive plants take over an area representing approximately 4,000 square miles, leading to billions of dollars in agricultural and forest product losses, and billions more in control costs. Your backyard may well represent a small but important skirmish in this chilling invasion scenario.

Invasive plants often dominate our personal landscapes. Often we inherit a property overrun with Japanese honeysuckle and English ivy, while at other times we ourselves are unwitting co-conspirators by purchasing and planting these exotic species, many of which represent the backbone of sales for garden centers, especially where groundcovers are concerned.

Of course, selecting these traditional invasive species is understandable enough. Non-native plants are generally inexpensive, readily available, and easy to maintain; after all, they really do grow and spread like weeds. And that’s just the problem! Or at least a part of the problem.

Non-native invaders damage our environment in numerous ways. The green scourge of kudzu in the Southeast has effectively conquered seven million acres of forest at a loss of 50 million dollars, and is now romping through wooded areas up and down the East Coast (and beyond). It smothers trees up to 100 feet tall, and overwhelms the natural landscape, much like multiflora rose, Asian wisteria, porcelainberry, and sharp-barbed mile-a-minute vine.

But there is an even more insidious side to this invasion. Exotic species also successfully (and insidiously) out-compete and replace native plants like horticultural body snatchers. This loss of native plants represents an overall loss of habitat and food sources for native wildlife. Consider the impact of the Bradford pear and its overuse as a street and landscape tree. Unlike a native ornamental tree, such as a viburnum or red chokeberry, which can provide food for dozens of bird species, the brittle Bradford pear attracts only European starlings, a winged plague in their own right, which help carry the invader's seeds far and wide in an example of sinister symbiosis.

English ivy is another example. It displaces native ground covers, inevitably escapes into natural areas, and eventually mutates from ground cover to tree strangler. Even well-manicured ivy beds around the home are potential fifth-columnists, as the seeds produced by the vine are favored by non-native birds, like our pesky starlings, and distributed over a wide area far beyond your backyard.

Unfortunately, the invasion can never be completely halted. Once a non-native species is successfully introduced, it is almost impossible to eradicate it completely. However, we can strike an effective blow for biodiversity in several important ways. First, know your enemy.

Find out more about which species are invasive, and NEVER consider purchasing or planting them. Besides those already mentioned, it is disappointing to note that a number of other vicious invaders are still sold as landscape ornamentals, including porcelainberry, Oriental bittersweet, and Japanese honeysuckle. Also invasive are popular groundcover standards like periwinkle and bugleweed (ajuga).

And, to aggravate the problem, mail order and Internet shopping has encouraged homeowners to buy species which should not be planted locally, or otherwise offer false claims about a specific variety being non-invasive. For example, horticultural writer Kathleen Fisher notes that gardeners in the Washington metropolitan area continue to plant purple loosestrife, an unstoppable invader of wetlands, perhaps due to an erroneous newspaper article touting a sterile cultivar. Not true. Keep away from this marauder and plant gayfeather (Liatris) instead.

Next, seek sensible alternatives. Most of the desirable characteristics sought in exotic species can be found in native plants. Substitute native ferns, golden ragwort, green-and-gold, native ginger, or Allegheny spurge for invasive ground-covers. Or, at least, select a non-invasive ground cover, such as pachysandra or sweet woodruff.

Invasive and almost clich├ęd hedges and foundation plantings like burning bush euonymus and Japanese barberry are more handsomely replaced with avian favorites such as winterberry, beautyberry, or inkberry. Privacy plantings like Leyland cyprus and the double threat of autumn and Russian olive can be replaced with American holly or eastern red cedar. Exotic species are very often easily identified by their common names: Japanese honeysuckle, Norway maple, Asian wisteria, Chinese bittersweet — and they are just as easily replaced by their native American counterparts, all of which are better suited to our bioregion, and more suitable for our resident wildlife.

Lastly, take up arms against the invaders. It is not going to be an easy fight. Ivy and honeysuckle will need to be cut, yanked, and grubbed up from the soil. And the fight will not be won overnight. Eradicating the most aggressive vines and ground covers will require constant vigilance and patience. Addressing larger plants, like shrubs and ornamental trees, will require some soul searching. It is never emotionally easy to cut down a tree, with the exception of a Bradford pear, which has probably lost half of its branches already. Moreover, a significant financial investment has often been made in these plantings. Perhaps the best solution in these cases is to defuse some of the alien invasion by expanding your current landscaping plan to include numerous native planting areas.

Copyright 2009, Joseph M. Keyser

Invasive Alien Species


Catalpa Catalpa spp.
Empress Tree Paulownia tomentosa
Norway Maple Acer platanoides
Sweet Cherry, Bird Cherry Prunus avium
Tree of Heaven Ailanthus altissima
White Mulberry Morus alba
White Poplar Populus alba
White Spruce Picea glauca


Cinnamon Vine Dioscorea oppositifolia
Climbing Euonymus Euonymus fortunei
English Ivy Hedera helix
Japanese Honeysuckle Lonicera japonica
Kudzu* Pueraria lobata
Mile-a-minute Polygonum perfoliatum
Oriental Bittersweet Celastrus orbiculatus
Periwinkle Vinca minor
Porcelain Berry Ampelopsis brevipedunculata
Wisteria Wisteria floribunda, W. sinensis

Herbaceous Plants

Beefsteak Mint Perilla frutescens
Bull Thistle* Cirsium vulgare
Canada Thistle* Cirsium arvense
Common Daylily Hemerocallis fulva
Creeping Bugleweed Ajuga reptans
Creeping Lilyturf Liriope spicata
Crown-vetch Coronilla varia
Eulalia (ornamental grass) Miscanthus sinensis
Garlic Mustard Alliaria petiolata (A. officinalis)
Giant Chickweed Myosoton aquaticum
Giant Knotweed Polygonum sachalinense
Ground Ivy Glechoma hederacea
Henbit Lamium amplexicaule
Indian Strawberry Duchesnea indica
Japanese Knotweed Polygonum cuspidatum
Japanese Stiltgrass Microstegium vimineum
Johnsongrass* Sorghum halepense
Lesser Celandine Ranunculus ficaria
Moneywort Lysimachia nummularia
Mugwort Artemisia vulgaris
Musk Thistle* Carduus nutans
Nodding Star of Bethlehem Ornithogalum umbellatum
Plumeless Thistle* Carduus acanthoides
Purple Dead Nettle Lamium purpureum
Purple Loosestrife Lythrum salicaria
Reed Canary Grass Phalaris arundinacea
Shattercane Sorghum bicolor
Spotted Knapweed Centaurea maculosa
Star of Bethlehem Ornithogalum nutans
Tall Fescue, K31 Fescue Festuca elatior
Wild Garlic* Allium vineale

*Regulated by state or federal law.

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