CIPC - Priority Invasive Plants

There are a number of invasive plant species in Coastal BC.
Download our most recent priority list here (PDF - 38KB)

Scotch Thistle

Scotch thistle (Onopordum acanthium) is an impressive garden ornamental that can grow up to three meters tall! However, the ability of one plant to produce thousands of seeds that can remain viable in the soil for over 30 years makes it an aggressive opponent to even the greenest of thumbs. Scotch thistle is highly invasive and can easily “hop” the garden fence into native habitat through its windborne seeds. The detrimental effects of this species are being felt by wildlife, livestock and field crops. It can grow in dense patches where the sharp spiny stems prevent the passage of both animals and humans, restricting access to important animal habitat and recreational destinations. Since scotch thistle is growing in gardens on Vancouver Island and surrounding Coastal communities, there is concern that its impacts may increase as it continues to escape controlled garden environments to invade our natural areas.

Scotch thistle is a tall thistle with multiple flower heads, each growing to five centimeters wide. The leaves are very large and irregularly lobed with sharp yellow spikes along the edges. Upper and lower leaf surfaces are covered with a thick mat of cotton-like or woolly hairs, giving the foliage a grey-green colour.

A small cluster of plants can either spread immediately or over many years. Because the seeds remain viable in the soil for so many years, patches in your garden may already harbour a large seed bank in the soil below the plant.

As a resident, you can help control the spread of this invasive species by removing all plants from your property. Plants can be cut, taking care to prevent seed spread, and then the roots dug up. Scotch thistle can re-grow from severed roots, so care must be taken to remove all plant parts from the soil and avoid spreading them through garden waste, dumping, or vehicles. For other control options, see http://www.weedsbc.ca/pdf/scotch_thistle.pdf.

Additional Information:
www.agf.gov.bc.ca/cropprot/weedguid ...

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