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Have you ever stopped along a country roadside and dug up a flowering plant near the edge of a drainage ditch, thinking it would make a lovely addition to your garden? Or made a fall wreath from a climbing vine with gorgeous orange berries, then later tossed the wreath into the bushes out behind the garage?

Or maybe you’ve decided to let a piece of the lawn go wild to reduce mowing, or bought a piece of land that once pastured farm animals, but has gone “back to nature” because you keep no livestock.

That’s how I got purple loosestrife, a plague of Asian bittersweet, and acres of a thorny shrub called autumn olive. My “backyard” also sports impermeable hedges of Japanese knotweed (aka “bamboo”) plus multiflora roses and Japanese barberry. All of these plants are listed and regulated as “invasive species” in my home state of New Hampshire.

Once established, these non-native plants become challenging or even impossible to remove before they completely dominate a landscape.

What is an ‘invasive’* plant?

So-called “invasive” plant species generally refer to non-native (aka “alien”) plants that spread rapidly and threaten economic harm or the health of native ecosystems. Most states have enacted laws and regulations forbidding the sale, importation, or propagation of such species.

According to the Nature Conservancy, invasive species cost the U.S. economy $120 billion a year, with over 100 million acres (an area roughly the size of California) suffering from invasive plant infestations.

All plants have some geographical point of origin, an ecosystem where they co-evolved with numerous other plants, animals, and microorganisms over millennia, to the point where they keep one another’s populations in check.

To thrive, plants have evolved many ingenious ways to distribute themselves, among them

• Root systems that spread rapidly and invisibly underground.
• Seedpods that explode when ripe, spitting their seeds far and wide.
• Seeds so light they can float long distances on the wind.
• Seeds carried in the digestive systems of animals that eat their fruits and deposit the seeds some distance away in a little packet of scat that helps fertilize the ground they fall on.
• Seeds with barbs or burrs that stick to the fur of passing animals that transport them to new ground.  

Humans took favorite plants with them as they traveled to explore, settle, and exploit new lands, a practice very much with us today. More recently, people have imported non-native species to introduce as ornamental specimens to gardens, to control erosion on disturbed construction sites, or for other purposes. Still other invasives hitched rides on ships transporting agricultural, forestry or other products.

In their new habitats, some (not all) non-native plants spread rapidly, since their new surroundings lack the plant diseases, predators, and strong competition from other plants that kept them under control in their native ecosystems.

Invasives include vines, grasses, herbaceous flowering plants, shrubs, and trees. Invasive vines may strangle native trees and shrubs; grasses, herbaceous species, and shrubs may crowd out native plants. They may reduce biodiversity by strangling or crowding out native species, degrade and destroy habitat, and destroy food webs by providing wildlife with less nutritious seeds or fruits than native plants.

Aquatic/wetland invasives are often spread between and among waterbodies by boats, trailers, and other recreational equipment. These plants may crowd out organisms within the ecosystem, clog waterways, kill or alter the balance of aquatic life.

How to stop the spread of invasive plants

If you’re a landowner, a gardener or farmer, a pond owner, a recreational boating enthusiast, or simply a citizen concerned about the health of your local environment, there are things you can do to help stop the spread of invasive plant species:

• Learn to recognize by sight the invasive species in your area and point them out to others.
• Don’t dig anything from the wild unless you’re certain it’s not invasive (or endangered).
• If you do see an invasive on you own property, dig it up, smother it, or follow instructions from your state’s invasive species program. Severe infestations may require herbicides.
• Plant native shrubs and flowers. They not only provide best food and shelter for native wildlife and protect the environment from spread of harmful weeds, but they are also easier to maintain.