Invasive Plants

Gardening by the Yard : Episode GBY-1111 -- More Projects »
Which plants should be avoided in your neck of the woods? That's a good question to ask, says master gardener Paul James.

"One of the hottest topics in the world of gardening is invasive plants, and it's also one of the most misunderstood."

Invasive plants, also known as alien or even exotic plants, are those that are extremely adaptive and can quickly spread and take over native plant populations as well as food crops. In addition, invasive plants may also threaten animal populations by destroying their habitat and food sources. In fact, invasive plants cause more than $100 billion in damage in the U.S. alone.

Nearly all invasive plants, including common weeds, came to this country from somewhere else. Some arrived accidentally, perhaps in the form of a seed hitching a ride on someone's shoe, as a volunteer in a shipment of nursery plants, or introduced on purpose as ornamentals. Of course, when introduced, no one knew the plants would be invasive because in their native land--whether China, India or the South of France--they weren't invasive at all.

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Figure A
One of the most curious and confusing aspects of invasive plants is that they aren't necessarily invasive in all parts of the country or the world. For example, pampas grass, which is native to southern South America, is a hugely popular ornamental grass in large part because of its magnificent plumes (figure A). "It's as tame as my dog Maggie in my Oklahoma landscape as well as much of the rest of the country," says James, "but in California it can be extremely invasive."

The same can be said of many other plants that have made the invasive list, nearly all of which you could no doubt easily find right now at your local nursery or lawn-and-garden center. In fact, the U.S. Department of Agriculture's list of invasive plants includes some pretty surprising entries, many of which are plants that are not only readily available and commonly grown but actually take center stage in gardens all over the country. Some surprisingly invasive plants, depending on region, include nandina, parsley, daylilies, black-eyed Susans and even Japanese maples.

Thankfully, most landscape plants are well-behaved and that's particularly true of native plants. But a good many plants sold at your local nursery--both native and non-native--may pose a threat to your landscape. For example, according to the Florida Department of Environmental Protection, at least 39 percent of the worst invasive species in that state are still commercially available. Yet, rarely are those plants labeled as being potentially invasive. Again, some plants may be relatively tame in your area--for instance, burning bush (Euonymus alata) in James' area--but all have the potential to grow out of control.

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Figure B
Invasive plants are more of a problem in some areas than others. For example, invasive plants are a huge problem in California, Florida and Hawaii. Other hot spots include much of the Southeast and Gulf Coast, as well as all the way up the entire length of the Eastern seaboard. "Curiously, although the USDA's list of invasive plants is extensive, it doesn't include a number of readily available landscape plants that I would consider invasive in certain settings--such as Phyllostachys bamboos or catnip (figure B)."

So what can you do? Here are some points to ponder:

  • A plant that's invasive in the East isn't necessarily invasive in the West, and visa versa. There are a number of plants that behave beautifully in one part of the country while being a complete nuisance in another.

  • Familiarize yourself with plants considered invasive in your area and refrain from planting them. And, by the way, invasive plants may include both terrestrial as well as aquatic plants. You might also ask local plant retailers to either clearly label or stop selling plants that are known to be invasive in your area.

  • James recommends that you not grow these plants no matter where you live:

    white poplar
    black locust
    shrub honeysuckles
    smooth and glossy buckthorn
    winged euonymus or burning bush
    purple loosestrife
    dame's rocket
    giant reed grass (Arundo Donax)

    These plants are considered invasive or at least potentially invasive throughout most of the US.

  • Realize that many individuals and organizations in the gardening industry are working hard to increase the awareness of invasive plants, control their spread and prevent any new arrivals of invasives into this country. All they ask is that we do our part to not plant any known invasives in our gardens.
    • Also in this Episode
    Gardening by the Yard : Episode GBY-1111
    •Invasive Plants
    •Building Berms
    •Early-Bird Bloomers
    •Curbing Crabgrass