Coastal Invasive Species Committee


Giant Hogweed (Salt Spring Island Concervancy)


by Jean Wilkinson, Stewardship Committee, Salt Spring Island Conservancy

"Giant Weed That Burns and Blinds Spreads Across Canada" (National Post, July 13, 2010) "Hogweed Response Team in the Works" (The Province, July 14, 2010) "Huge Noxious Weed Poses Health Risk" (Victoria Times Colonist, July 15 2010) "Giant Hogweed Leaves Mark (Gulf Islands Driftwood, Aug 4, 2010)

Giant Hogweed made headlines last summer because it presents a serious and growing public health hazard. It's a very tall plant, native to Asia, and was introduced to Europe and North America as an imposing ornamental or curiosity. It has escaped cultivation, is highly invasive, and is currently found in B.C. in Greater Vancouver, Central to Southern Vancouver Island and the Gulf Islands, including Salt Spring.

Contact with Giant Hogweed's stems or leaves can cause severe burns, blisters and scarring of the skin. The sap contains photosensitive chemicals that become toxic in the presence of sunlight. Because of this, the effects may not be noticed for several hours. This makes the plant especially dangerous for children, who may be attracted to such an unusually large plant and have been known to use the thick hollow stems for "pea-shooters" or "telescopes". The skin will first redden and blister, and painful inflammation follows 2 or 3 days later. The affected skin will often darken after a week and may remain dark for years. Hospitalization may be necessary, and the presence of minute amounts of sap in the eyes can lead to temporary or even permanent blindness. The chemicals in the sap are carcinogenic and can cause birth defects.

Clearly it is in everyone's interest to get rid of Giant Hogweed infestations and stop the spread of this plant! Since it dies down each winter and grows up to 6 metres tall in the summer, it is recommended to remove it in February through April, when it is just sprouting and more easily dealt with. So if you notice any tall dead stems in the winter, or recall seeing an unusually large plant with big leaves in the summer, check the area for new growth in the spring. If you suspect you've found a Giant Hogweed plant, please report it by calling 1888-WEEDSBC.


Identification – Heracleum mantegazzianum) – very large perennial up to 6 metres tall with deeply incised compound leaves as big as 1.5 metres across. The stem can vary from purple to mostly green with purple blotches, and has distinctive bumps with stiff white hairs along it. Each fall the plant dies back until spring. After a few years' growth it blooms in summer, with large (up to 1 metre across) umbrella-shaped clusters of small white flowers at the top. After seeds have set the individual plant generally dies.

Look-alikes – Common Cow Parsnip, Palmate Coltsfoot, Poison Hemlock, Queen Anne's Lace (Wild Carrot) all look similar but much smaller

Impacts – poses serious public health risks as outlined above, reduces access to streams and riverbanks, and increases risk of erosion as native vegetation is shaded and killed, leaving the soil unprotected during winter rains

Found –in moist to wet areas near streams, creeks, ditches, rivers, along roads, in vacant lots and some gardens

Spreads – the plant produces numerous flattened, oval seeds which drop on nearby soil, are blown by wind and float down streams

Control – Cut the plant roots 10 to 15 cm below the soil surface with a sharp knife or long-handled narrow shovel. Try to minimize soil disturbance. Do not use a weed-whacker. Monitor the site for 3 to 5 years to remove any new growth. If the plant has bloomed, do not transfer any soil from within 4 metres as it may contain seeds.

CAUTION Prevent skin contact. Wear heavy, water-resistant gloves and coveralls. Many fabrics soak up the plant sap, which can then transfer to skin. Plant "hairs" may also penetrate thin clothing. Wear goggles when disturbing or removing plants, as small droplets of sap may be released into the air. Dispose of or wash tools, gloves and clothes thoroughly with soap and water.

FIRST AID If any sap contacts skin, wash carefully with soap and cold (not hot) water. Keep exposed areas away from sunlight for at least 48 hours. If rash or blistering develops, consult a physician. If sap gets into the eyes, flush with large amounts of water, use sunglasses and see a physician at once.

Disposal – Put plant parts in double plastic bag marked to indicate that contents can cause skin damage, and take to transfer station. Note: Do not compost or chip these plants.

Alternatives - Recommended non-invasive replacements include native species Blue Elderberry, Sea-coast Angelica and Kneeling Angelica and exotics Rodgersia, Chinese Rhubarb, Astilboides and Ligularia

More Info: Salt Spring Island Conservancy Stewardship Committee 250-537-4877, Coastal Invasive Plant Committee , Invasive Plant Council of B.C.