Ministry of Agriculture
Invasive Plant Alert
Prevent the Escape of Aggressive Plants
A threat to B.C.'s resources
Wild flowers or Invasive Noxious Weeds?
Foreign plant species escaping from the garden or landscape can have a devastating impact on native plants and animals. Please help in protecting the natural environment of British Columbia!
B.C.'s noxious weeds are typically exotic or non-native plants that have been introduced to this province without their natural predators. Left unchecked, these weeds destroy our native plant and animal habitat. They are among the top cause for losses in the natural diversity of our environment, and are devastating to the economy. Weeds cause crop losses well in excess of $50 million annually in B.C.
Invasive plants have the capacity to move into a habitat and reproduce so aggressively that they displace the original vegetation. They:
- crowd out native plants, including rare and endangered species
- destroy wildlife habitat
- reduce crop yields (on average 10 to 15 %)
- reduce crop quality (taint food products with off flavours, toxic berries, spines, etc.)
- poisonous weeds are a danger to humans, livestock, and wildlife
- dry weeds create a fire hazard; tall weeds along roadsides create a traffic hazard; aquatic weeds pose a danger to swimmers and boaters
- provide refuge for insects and diseases that attack adjacent crops and beneficial plants
- lower property value
- reduce aesthetics of an enjoyable landscape
- reduce soil stability and water quality
- cause physical discomfort to recreationists due to spines, burrs, prickles
Purple loosestrife, English ivy, Dalmatian toadflax, Scotch broom, field scabious, Oxeye daisy, giant hogweed and Japanese knotweed (bamboo) are but a few examples of horticultural plants that have escaped and caused extensive economic and environmental damage in various regions of B.C. They were introduced through the sale of seeds, cuttings, etc targeted for the home gardener for use as birdseed, for wildflower landscapes or as medicinal herbs. Ragweed, a plant that is quite rare in B.C., has recently been found growing under bird feeders at a number of locations.
Noxious weeds have gained a foothold in B.C. through accidental introductions by various mechanisms including: wind and water; unloading of ship ballast; hitchhiking on vehicles, boats and heavy equipment; contaminated crop seed; wildlife, etc. Seeds, cuttings or bulbs of virtually any worldwide noxious weed are available through the mail or the Internet. These plants are sometimes used for research purposes but many are also used for landscape or medicinal/herbal purposes. Unfortunately, some noxious weed infestations have also resulted from purposeful introductions as garden and landscape plants. Ideal characteristics for the garden, such as adaptability, vigorous growth and establishment, self-seeding ability, and persistence are the same characteristics that threaten our natural resources once these plants escape the garden.
In Canada, the Seeds Act regulates allowable weed seed content of crop seed and the Plant Protection Act regulates import of a few parasitic plants. Currently there is no federal noxious weed legislation that specifically regulates the import of aggressive or potentially noxious plants for landscape and garden use. The BC Weed Control Act places a duty on all land occupiers to control noxious weeds listed in the Regulations. In B.C., there are 47 plant species that are classified as Noxious. These must not be transported to or seeded in areas where they are not already established.
Non-native garden seeds
These are offered for sale with the best of intentions; the creation of a pleasing, colourful landscape or for their herbal properties. Some of these plants are classified as noxious in B.C. or are recognized as being so in other jurisdictions. Some species are close relatives of known invasive plants and may also have aggressive tendencies. In most instances the species offered for sale are not a threat to the environment and serve their intended purpose without threat to our natural resources.
Undesirable plant species
Deciding what plant species might be undesirable in a given area would be an exceptionally difficult task. Each species would have to be judged on its individual potential to escape and invade native landscapes. The following list contains a few examples of aggressive ornamental or herbal species that have escaped the garden and are available for purchase through various sources.
- Baby's-breath (Gypsophila paniculata)
- Burdock (Arctium lappa)
- Common tansy (Tanacetum vulgare)
- Cypress spurge (Euphorbia cyparissias)
- Dalmatian toadflax (Linaria dalmatica)
- Diffuse knapweed (Centaurea diffusa)
- English ivy (Hedera helix)
- Field scabious (Knautia arvensis)
- Giant hogweed (Heracleum mantegazzianum)
- Hound's-tongue (Cynoglossum officinale)
- Japanese knotweed (Mexican bamboo) (Polygonum sachalinense)
- Musk thistle (Carduus nutans)
- Orange hawkweed (Hieracium aurantiacum)
- Oxeye daisy (Chrysanthemum leucanthemum)
- Poison hemlock (Conium maculatum)
- Policeman's helmet (Impatiens glandulifera)
- Purple loosestrife (Lythrum salicaria)
- Scotch broom (Cytisus scoparia)
- Spotted knapweed (Centaurea maculosa)
- St. John's-wort (Hypericum perforatum)
- Yellow toadflax (Linaria vulgaris)
What Can You Do?
Learn about the potential aggressiveness of what you buy through mail-order seed catalogues, the Internet and other sources. Awareness is the key to preventing further losses to B.C.'s biodiversity due to introduction of invasive foreign plant material.
- Do not purchase legislated noxious weed seeds.
- Contain creeping plants. Grow them in containers.
- Don't let invasive plants go to seed.
- Control weeds growing underneath bird feeders.
- Grow alternative plant material. (e.g., substitute less aggressive plants for purple loosestrife)
- Keep aggressive plants from escaping your garden or landscaped area.
- Do not use roadside/idle area plants in flower arrangements
To learn more about B.C.'s noxious weeds contact your local Ministry of Agriculture office, or visit our website at: