Most gardeners have heard the story of the evil kudzu, the “Vine that Ate the South”. Originally introduced as an ornamental plant at the Philadelphia Continental Exposition in 1876 it remained benign until the mid 1930’s when it was planted extensively by mid-western farmers to control soil erosion caused by dust storms. Soon kudzu turned into a plague rather than a cure, swallowing up native plants, abandoned houses, broken down cars, telephone poles, in short, anything standing still. Most invasive plants are not quite as aggressive, and some can even serve useful purposes, but it pays to know which plants are likely to give a gardener a bad rep and a hard time. Here are a few of the worst culprits.
One of the top offenders is Euonymus alatus, Winged Euonymus or Burning Bush whose invading range extends from New England through the mid-west.
Brought into the United States in 1860 as a decorative shrub and prized for its brilliant fall foliage and corky stems, the fruit is much beloved by birds who then distribute the seeds far and wide. Once Burning Bush gets established it snuffs out all native plants in the vicinity so just be aware that if you decide to plant a Burning Bush, your neighbors a couple of miles away might be less than thrilled with your decision.
1860 also saw the introduction into the US of another ornamental shrub, Japanese Barberry, Berberus thunbergii (what were the Victorians thinking?).
Highly valued as a hedge it is easily shaped, has rich winter color, produces vibrant red berries and is deer resistant (deer have no taste for the thorns). As with Burning Bush birds disseminate the seeds of the red berries, and once they take root in woods and meadows they grow rapidly, forming dense thickets and smothering native plants. As if that was not curse enough, barberries harbor swarms of black-legged ticks, carriers of Lyme disease among other scourges. Difficult to eradicate with no known predators, the only way to control the spread of barberry is to dig it, burn it or zap it with Roundup. Because of its invasive habit many states have banned the sale or trade of Japanese Barberry.
Then there is a whole family of aggressive invaders, the Bamboos of which Phyllostachy aurea or Golden Bamboo is the black sheep.
A fast growing screening plant that quickly produces an impenetrable forest of slender stalks, bamboo falls into two categories – it can be either clumping or running. Although few nurseries sell the running variety because it literally runs amok, even clumping bamboo requires restraint, demanding either annual root pruning or enclosing the roots with a 30inch deep plastic barrier. Yet taking these precautions does not guarantee that it will behave – bamboo has been known to spring up 50 feet away from the mother plant and even jump driveways. Astonishingly one homeowner reported that bamboo shoots sprouted through his basement floor, not a dirt floor, a cement floor. The only sure fire way to keep it under control is to plant it in a container and treat it as a handsome specimen.
Invasive plants are not just limited to woody shrubs; some flowering perennials have made the hit list as well. The top contender for Evil Perennial of the Century is Purple Loosestrife or Lythrum salicaria, a stately plant with magenta flowers that often is spotted in wide swathes along the nation’s highways causing the occupants of passing cars to ooh and ah.
Perhaps they would hold their applause if they realized they were celebrating a plant that the World Conservation Union has labeled one of the world’s 100 worst invasive species. Yet despite condemnation by guardians of the environment, Purple Loosestrife still is widely available commercially; only a few states have banned its sale. Thought to have been brought to this country in a ship’s ballast, this self-sowing devil thrives in sunny wetlands, and its only known predator is a European beetle that feeds exclusively on the leaves. In an attempt to control the spread of Purple Loosestrife, many states have instituted programs to release these beetles into the wild, programs that have proved fairly successful thus far.
Another invasive species often sighted and sited beside roadways is the charming Ox-eye Daisy, Leucanthemum vulgare, whose bright white petals and golden yellow centers liven up long stretches of highway.
Often confused with its taller sister, Shasta Daisy (Leucanthemum x superbum) which is not invasive, the Ox-eye daisy can produce up to 26,000 seeds per plant, seeds so sturdy that even when buried they may remain viable for more than 25 years. Resistant to many herbicides, the most effective control is to dig the plant and destroy it, and for those gardeners thinking of planting a wildflower mixture, check the contents of the seed packet; often Ox-eye Daisy seeds are included.
An aggressive groundcover, Creeping Jenny or Moneywort thrives in sunny moist locations. Named for a Macedonian king Lysimachia nummularia spreads rapidly, its brutish behavior snuffing out lesser plants in its path. In spite of its reputation as a brute, Creeping Jenny serves as a colorful groundcover with its bright yellow flowers and penny-shaped chartreuse leaves; just be sure to keep an eye on it lest it breach its boundaries.
In spite of its popularity and widespread availability, the groundcover Vinca minor, or Myrtle is on many states’ list of nasty plants.
Introduced in the 1700’s for its medicinal properties, it quickly gained widespread adoption as an ornamental low growing plant – evergreen, easy to grow even in deep shade, and best of all, producing delicate blue flowers in early spring. An ideal groundcover one would think except for one drawback; it roots from the tips of runners forming a dense mat that smothers any plant in its way. Caution is advised when planting a vinca minor bed; it may branch out, spreading its long arms into unwanted places, the middle of your lawn, for instance. Since its waxy leaves repel most herbicides the only sure fire way to eradicate errant plants is to pull them up.
In addition to woody shrubs and perennial plants, two aggressive vines are renown for taking over their neighborhoods. The first, Lonicera maackii, Amur Honeysuckle was initially valued for its fragrant creamy white flowers, black berries and rapid growth,
but later reviled for its invading and marauding habit; many states have banned the sale and distribution of this honeysuckle. Brought to this country in the mid 19th century as an ornamental plant it turned out to be just as nasty as Japanese Barberry and Burning Bush two plants that arrived on these shores at about the same time. As is the case with many invasive plants, birds feasting on the berries can be blamed for the spread of honeysuckles, and with no known natural predators the only control methods are digging, burning or spraying with a glyphosate such as Roundup.
The final nasty plant selection Hedera Helix or English Ivy has been in this country since colonial days brought by the early settlers to add a touch of home to their gardens.
Growing in partial to full shade it makes an ideal woodland groundcover, but it also can morph into a vine, scrambling up tree trunks, blocking the sun and causing the decline and death of its host. In spite of its thuggish behavior many have been awed by the beauty of ivy-covered facades of many buildings on old college campuses (it is reputed that’s how the Ivy League schools got the moniker), but beauty is in the eye of the beholder; just ask any owner of a brick house who has footed the repair bill for the havoc wrecked by the tenacious tendrils of English Ivy.
This discussion only touched on the worst of the invasive plants; the list is extensive with new varieties added yearly – similar to the endangered species list, they both are expanding but one is threatened and the other is threatening. Just as gardeners check the sun and soil requirements before planting any new specimen, so too should they check the growth habit in case they inadvertently create a monster.
For More Information:
Euonymus alatus – Chris Borton CC BY-SA 3.0
Berberis thunbergii – Sage Ross
Phyllostachys aurea – Kurt Stuber
Lythrum salicaria – Saffron Blaze CC BY-SA 3.0
Leucanthemum vulgare – Derek Ramsey
Lysimachia nummularia – CC BY-SA 3.0
Vinca minor – Ryan Kaldori
Lonicera maackii – Wouter Hagens
Hedera helix – H. Zell