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Invasive Ornamental Plants

What are They and Why are They a Problem

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In times of drought, the use of xeriscape plants in the garden are highly recommended. While this is a wise idea for consumers to adopt, they must be careful as to which drought tolerant plants they select to be their next garden beauty. Most plants used for landscaping purposes lack the ability to proliferate outside of the cultivated environment of the home garden. Some plants however, were imported to the United States for their aggressive growth habits, xeriscape potential, or re-seeding capabilities. These plants are known as “Invasive Ornamentals”. The very traits that make these plants desirable for a garden or landscape, may also enable them to thrive outside cultivated areas and become fierce competitors with our native vegetation. People seeking color, vigor, and something special for their gardens have unwittingly brought these non-native species into our environment. Unfortunately, most individuals don’t realize that they may have opened a Pandora’s box in their plantings. These non-native, aggressive plants quickly escape and begin the demise of our native plant communities and some can be hazardous to humans. Myrtle spurge, for instance, contains a milky sap that is highly caustic to the skin. If children are playing in an area where this plant is growing and get the sap on their skin, painful rashes and blisters will soon follow.

A major hurdle in stopping the spread of Invasive Ornamentals is the misconception that something attractive can’t be a weed. On the contrary, species like oxeye daisy, myrtle spurge, and Russian olive have proven to be very ecologically damaging and difficult to control once unleashed on our native landscapes. Wildflowers such as Colorado Blue Columbine, our state flower, can’t compete with invasive ornamental plants for nutrients, sunlight, and water. As a result, our biologically diverse grasslands, mountain meadows, and wetlands are in danger of being overrun by invasive ornamental plants. Fortunately, there are plant choices available to the home gardener that provide similar colors and growth habits to these invasive ornamentals, but not the problems associated with them.

In 1999, the Colorado Department of Agriculture has adopted what is called the Colorado Nursery Act. Within this Act, there is a list of weeds that are prohibited for sale in Colorado. Colorado nurseries or garden centers are required by law not to sell or contaminate nursery stock with plant species that are included on this prohibited weeds list. Some of the species included are Russian olive, myrtle spurge, oxeye daisy, bouncingbet, dame’s rocket, purple loosestrife, and common St. Johnswort.

Unfortunately, there are still quite a few wildflower seed mixes that contain invasive ornamental plants. Even though it is unlawful to sell these plants or seed mixes containing noxious weed/invasive ornamental seeds, it is still possible to purchase them at quite a few chain stores in Colorado and on the internet. If you see these plants or their seeds for sale, please contact the Colorado Department of Agriculture at 303-239-4153.

Think native when choosing drought-tolerant plants for the garden. Contact the Colorado Native Plant Society for a list of native plants that do well in a garden environment. There are also many non-native plants that aren’t invasive and will do well in the garden. Ask your local garden center experts for alternatives to invasive ornamentals. They’ll be glad to help you.


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