Weed science Society of America Logo


Ornamentals Gone Wild: Weed Scientists Recommend Smart Shopping When Selecting New Flowers and Shrubs

Will that showy ornamental flower or shrub you purchased prove to be well behaved?  According to experts with the Weed Science Society of America (WSSA), it is important to be an informed shopper so you don’t end up with a costly nuisance.  Some ornamentals can be garden thugs that crowd out surrounding plants and travel well beyond where they were planted.

“The very things we value in ornamental plants can also translate into bully-like tendencies,” says Linda Chalker-Scott, Ph.D., urban horticulture extension specialist and associate professor at Washington State University.  “Some ornamentals spread quickly, grow densely and tolerate even the poorest of growing conditions.”

Experts say that many ornamental plants with troublesome tendencies are imports from other countries.  Once out of their native habitat, they often become more unruly.  Examples include:

  • Japanese barberry (Berberis thunbergii).  This dense, woody shrub is native to Asia.  It produces small yellow clusters of flowers, oblong red berries and colorful fall foliage.  It also is prized for its deer resistance.  But when Japanese barberry escapes into natural areas, it produces dense thickets that choke out native flowers, plants and tree saplings.  It also retains humidity, making it a perfect safe harbor for ticks that spread Lyme disease.
  • Scotch thistle (Onopordum acanthium).  A native of Europe and Asia, Scotch thistle was introduced in the U.S. more than 200 years ago.  In western states it has become a real pest and is now classified as a noxious weed.  It chokes out cultivated crops and native species, thrives even during drought conditions and can be extremely tough to eradicate.
  • Dalmatian toadflax (Linaria dalmatica). This pretty perennial belongs to the snapdragon family and is native to the Dalmatian coast of the Adriatic Sea.  But it has earned a reputation as a serious invader across much of the U.S. and Canada.  It is especially rampant in dry, open spaces, such as recreation areas, meadows and roadsides.  It can be toxic to livestock.
  • Tamarisk (Tamarix sp.).  An import from Eurasia and Africa, the tamarisk is a small tree valued for feathery plumes of pink flowers that bloom from late summer through early autumn.  But each flower can produce thousands of tiny seeds that can be carried by wind or water – making it easy for the tree to escape into areas where it can wreak havoc.  A single tree can consume up to 200 gallons of water a day.  Tamarisk can devastate wildlife habitats and drop salty secretions that taint the soil and make it impossible for native plants to grow.   Its thirsty ways can actually lower the water table.
  • Scotch broom (Cytisus scoparius).   An exotic shrub known for fragrant yellow flowers, Scotch broom is a native of western and central Europe.  But on the eastern and western coasts of the U.S., Scotch broom grows in dense stands that crowd out native species.  Each plant produces thousands of seeds that can remain viable in the soil for years.

Unfortunately, these and many other ornamentals with invasive properties are still available online and through local garden centers and home improvement stores.  As a result, experts say, it is important for buyers to beware.

“Shoppers should research their options before going to the garden store,” says WSSA member Mark Renz, Ph.D., assistant professor at the University of Wisconsin and president of the Midwest Invasive Plant Network (MIPN).  “If the plant you were considering has invasive tendencies, substitute a related plant or cultivar that is better behaved.  Often there will be many noninvasive plants that have the traits you are after.”

Renz recommends searching the USDA’s National Invasive Species Information Center website (www.invasivespeciesinfo.gov) to see if the plant you are considering is on their watch list.  You might also consult your local botanical garden, a regional Exotic Plant Pest Council (www.naeppc.org) or local horticulturists and conservationists.

In addition, MIPN offers a free mobile app that can help those who live in the Midwest identify landscape alternatives to the region’s invasive ornamental plants.  Simply search for “landscape alternatives” in the app section of your smartphone or tablet.  Printed brochures of the same information can be ordered at www.mipn.org/publications.html.


About the Weed Science Society of America

The Weed Science Society of America, a nonprofit scientific society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Weed Science Society of America promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, fosters awareness of weeds and their impact on managed and natural ecosystems, and promotes cooperation among weed science organizations across the nation and around the world.  For more information, visit www.wssa.net.