Invasive Species Council of Manitoba: Giant Hogweed

Giant Hogweed

Heracleum mantegazzianam

Aka Giant Cow Parsnip

The Giant Hogweed is a short lived perennial, it grows as a rosette with large leaves for the first few years until there is enough reserve in the tap root to reach the flowering stage. At this point the plant will grow 3-5 m in height, flower, set seed, then die.

It's native to a small area between Russia and Turkey and was introduced to the rest of Europe and North America as an ornamental. It is now one of the largest herbs in Europe and is know to exist in the wild in B.C. and southern Ontario and other temperate areas in North America.

The stem is hollow and dark with reddish purple spots covered with hair that contains sap. This sap can cause sever injury, it causes the skin to become sensitive to UV radiation which causes painful burns and blistering.

The leaves are compound and have 3 leaflets that are deeply lobed and can grow as large as 1-1.5 m wide. The leaves shade out any competitive plants giving Giant Hogweed a competitive advantage. The leaves also contain hairs with sap that can cause burns and blisters.

The flowers are white compound umbels and can reach a meter across. Seeds can last longer than 7 years. Both seed and plant can not survive waterlogged sites but do prefer moist soils such as ones found in riparian habitat.

Do not purchase this plant or its seeds and do not touch it with bare hands. It's best to remove the plant when it is young and the tap root is small and be sure to wear protective clothing including gloves and goggles when doing so.

Information provided by Alberta Invasive Plant Council

Resources

Giant Hogweed Fact Sheet

Alberta Invasive Plant Council Fact Sheet

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Invasive Species Council of Manitoba

Giant Hogweed

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