Top 10 Most Invasive Plants in B.C.

Adorned with white flowers and huge jagged-edged leaves, the giant hogweed shoots up to a towering height of five metres (16 feet). This plant dominates the Lower Mainland, the Fraser Valley, the Gulf Islands and central to southern parts of Vancouver Island.

The sap on giant hogweed leaves is extremely dangerous when touched, causing burns, blistering and scarring on the skin. To remove the hogweed, a professional is highly recommended. If you must do it yourself, wear eye protection and waterproof gloves and gear at all times when removing flower heads and cutting root crowns. Do not touch your skin with the gloves and clean or dispose of them afterward.

With 20-200 flower heads per plant, the common tansy boasts vibrant yellow petals and stems as high as 1.8 metres (6 feet). It is widely distributed across the province, but is particularly prominent on the southeast coast of Vancouver Island, in Bulkley-Nechako, Squamish/Pemberton, Gulf Islands, Sunshine Coast, Central and East Kootenay, Columbia-Shuswap, North and South Okanagan, Greater Vancouver and the Fraser Valley.

Considered noxious by the Weed Control Act, infestations of the common tansy can be toxic for farm animals. They can also displace native plants. Be warned: Occasional mowing will only trigger an increase in plant growth. You must use both herbicide and mowing to effectively eradicate the common tansy.

4. Common Periwinkle (Vinca minor)

Common periwinkle may look pretty (and was intentionally introduced in the 1700s as an ornamental, fast-growing ground cover), but it is rapidly spreading through B.C.’s rainforests and harming native plant species. Periwinkle is primarily found in the Lower Mainland, Vancouver Island and the Gulf Islands. Dispose of periwinkle chemically or by securely bagging the removed plant. P.S., periwinkle is still sold throughout the province—so keep an eye out to avoid it in your garden.

Labelled noxious under the BC Weed Control Act, spotted and diffuse knapweeds negatively transform the landscapes of the Omineca, Peace River, Kootenay, Okanagan, Thompson and Cariboo regions. Because they spread so quickly, there are concerted efforts to try and minimize knapweeds in southern B.C.

Spotted knapweed have purple or white flowers with black tipped flower head bracts, while the diffuse knapweed have white, rose-purple or lavender blossoms in clusters. Knapweeds intensify erosion and runoff, displace native plants and kill vital forage for livestock. When dead, its materials increase the chance of wild fires. Eliminate the plant by hand pulling, cutting or mowing. Remove all roots to prevent regrowth and revisit the spot every so often to avert further growth.

Rapidly spreading throughout the eastern and western B.C., invasive hawkweeds are threateningly abundant in southern Kitimat-Stikine, Bulkley-Nechako, Cariboo regions and Fraser-Fort George region. While the majority of hawkweeds have bright-yellow blossoms, the only hawkweed identified as noxious by the Weed Control Act is vibrantly orange. Menaces to both the forest and livestock industry, hawkweeds displace native plants, reduce forage, and invade undisturbed natural areas.

Orange hawkweed is a concern for Kootenay, Okanagan, Thompson, Omineca and Peace River regions, as anything from agriculture and wind to recreational activities can spread this plant. To get rid of small infestations, dig out the flower and its roots, but ensure that none of the plant parts scatter as they can easily regrow from these fragments.

Capable of growing through house foundations and cement, the Japanese knotweed possesses stout reddish-brown stems, rough heart-shaped leaves and seasonal greenish-white flowers. Its favourite hangouts include roadsides, waste sites, wooded areas and waterways in the lower Fraser Valley region.

A born survivor, this plant can grow up to 3 metres (10 feet) in a year and can worm its way into new territories simply with root fragments. It clogs waterways and deteriorates native plant communities. It’s not just Japanese knotweed to look out for. All four species of knotweed in British Columbia (giant, bohemian and Himalayan knotweed) grow quite aggressively.

To eradicate the Japanese knotweed, remove existing stems, cover the area with plastic tarps during the fall and, finally, dig up rhizomes to prevent further growth. Since it will not compost properly, this knotweed must be bagged and buried deep in a landfill.

Reaching as high as 3 metres (10 feet), the Scotch broom can be recognized by its ridged green or brownish green stems and vivid yellow flowers. It flourishes in sandy soils, haunting the terrains of southern Vancouver Island, west of the Coast-Cascade mountains, the Queen Charlotte Islands, the southern interior and the Lower Mainland.

The Scotch broom releases toxic substances into its surroundings, restraining the growth of native plants and causing seasonal allergies. It is also toxic to livestock. It establishes menacing colonies and hinders the activities of large animals. The worst part? Each pod contains three to 12 seeds that can survive over 30 years.

Eliminate the Scotch broom by removing it before the flowering stage. Hand-pull the smaller ones and keep your eyes on the area every so often. For deep-rooted plants, remove with large tools, such as a shovel or saw.

10. Yellow Flag Iris (Iris pseudacorus)

From 40 to 150 cm tall, the yellow flag iris is distinguished by bold yellow flowers and long leaves. This species is generally located along riverbanks, marshes and lakes in southern parts of B.C. The yellow flag iris does not only reduce water flow, but also displaces native plants, consequently damaging the wildlife habitat. What’s more, the rhizomes are poisonous when ingested by cattle.

The most effective technique to eradicate this species is by carefully hand-pulling or cutting until the entire plant is completely removed. Since its leaves and rhizomes lead to skin irritation, it’s vital that you wear gloves and protective clothing. Do not compost; always throw it away as garbage.

This story was originally published in August, 2012 and was updated in August, 2025 with information from the Invasive Species Council of BC.