Potentially Invasive Ornamental Weeds

An Introduction to Potentially Invasive Ornamental Plants

What makes a plant invasive?
Plants become invasive when they are easily spread by seeds or roots. Invasive plants compete with and replace other plants. They may develop their own ecosystem at the expense of other desirable vegetation. We often refer to these as weeds.

The definition of a weed is a plant that intrudes into an area so as to injure or exclude desired plants. An invasive ornamental plant has the potential to become a weed.

The North Dakota noxious weed list is comprises of weeds that are required to be controlled by law (NDCC Chapter 4.1-47). Internet and catalog sales have made a large variety of plants available to everyone, including ND noxious weeds and potential ornamentals.

It is your responsibility to know what kind of plant ornamentals you are getting before you purchase, exchange, or dig up a plant to be placed on your property. Just because a plant is attractive, it may not be a desirable choice for your landscape or the environment.

Wildflower and seed mixes sold in the garden section of national retail stores or on the Internet may contain ND Noxious or Potentially Invasive Ornamental Plants. Always check the label before you purchase these seed mixes.

We Recommend
DO purchase plants recommended by the locally-owned nursery. Try to find out as much as possible about the cultural requirements of the plant:
Does it self-seed?
Will it spread by rhizones or stolens
Will it become an "escapee" into the surrounding ecosystem and compete with native plants for resources?

DON'T purchase a plant that is not properly labeled. If the store selling it doesn't know what it is and how it will adapt to the North Dakota environment, then don't take any chances.

USE CAUTION when purchasing plants over the Internet or garden catalogs. You don't get to select the plants and you have no guarantee that what you are ordering is what you are going to get.

TAKE ACTION. If you purchase a plant that is known to be invasive, keep the root system in check, such as planting the specimen in a large container in the ground which is commonly done with sumac.

Common Invasive Ornamental Plants
Yellow Toadflax (Linaria Vulgaris) is a perennial that reproduces by seed and underground roots. It is also know by the common name “Butter and Eggs”. It has a bright yellow, snapdragon-like flower with leaves that are long and narrow and attached directly to the stem. Yellow Toadflax is an aggressive invader with an extensive root system that makes this plant extremely difficult to control.

Oxeye Daisy (Leucanthemum Vulgare) has a white daisy-like flower that blossoms from June to October. The plant will aggressively reseed and quickly become naturalized. 

Common Tansy (Tanacetum Vulgare) was brought in by early homesteaders as a garden ornamental and for medicinal uses. The dark golden brown “button” flowers which lack ray petals are still used in commercial floral arrangements. The plant is toxic is consumed in sufficient quantity. It is spread by seed and by rhizomes. The plant is difficult to control culturally and with herbicides.

Queen Anne’s Lace (Daucus Carota) is also known as Wild Carrot, Bird’s Nest and Lace Flower and is a biennial which reproduces by seed. This plant, introduced as an ornamental, has a seed head made up of many small white flowers that develop into a flat-topped, 2-3” diameter head. It is a member of the parsley family.

Buckthorn (Rhamnus Cathartica) is a glossy-leaved, deciduous shrub with opposite or sub-opposite leaf arrangement. It produces a black berry that is readily consumed by birds. The seed passes through their digestive system, resulting in the plants establishing almost anywhere, and crowding out more desirable native plantings or disrupting the natural ecosystem.

Japanese Knotweed or Giant Knotweed (Fleece Flowers) are extremely invasive, spreading via rhizomes and seeds. Plants appear to have an allelopathic effect on other plant material, making re-establishment of desirable species difficult. The stems are hollow, bamboo-like, erect and no branches or with a few branches toward the tip. Plants can grow to a height of 8 to 13 feet. Herbicides are not effective in destroying these plants.

Ornamental Grasses 
Fountain Grass (Pennisetum Alopecuriodes) is of the dwarf fountain grasses with narrow green leaves, forms dwarf arching clumps. Even though it is a Zone 5 perennial, this species can re-seed causing it to be a problem.

Japanese Silvergrass or Amur Silvergrass (Miscanthus Saccharigloruscan) can reach a height of 6 feet. It spreads aggressively by rhizomes if left in an uncontrolled environment.

The spurge family includes weeds, garden ornamentals and houseplants. All spurges have small, but often colorful, showy flowers. They also have a milky sap which contains a variety of toxins. All parts of the plant that contain sap are toxic, thought the sap itself is the most toxic. Even dried plant materials retain their poisonous properties.

 Other plants in the spurge family are Croton (Croton Texensis), Poinsettia (Euphorbia Pulcherrima), Crown of Thorns (Euphorbia Milii) and Castor Beans (Ricinus Communis).