Tansy Trouble: A Guide to Stopping Common Tansy in Its Tracks
Tuesday, July 29, 2025
Have you spotted this notorious invader creeping into your pastures, along stream banks, or in disturbed sites? Common tansy, originally brought to North America for ornamental use and herbal purposes, may look harmless with its vibrant, sunshine-yellow flowers and tall, lanky stems reaching up to four feet. However, this seemingly cheerful plant is a formidable threat.
While it’s true that tansy contains toxic alkaloids, making it dangerous to livestock and humans if consumed in large amounts, animals generally avoid it due to its strong odor and bitter taste. Still, common tansy is far more dangerous as an aggressive competitor, crowding out native plants and leading to a steep decline in biodiversity. Left unchecked, it can rapidly dominate landscapes, threatening local ecosystems and agriculture. For these reasons, common tansy is designated as noxious under the Weed Control Act in Alberta.
Growth Habitat & Reproduction
Common tansy thrives in disturbed areas, such as roadsides, stream banks, pastures, and other sites where vegetation is sparse. Its seeds are easily spread by birds, animals, and vehicles, and once they find their way into the soil, they can remain dormant for up to 25 years. When they finally germinate, tansy can quickly take over, crowding out native species and destabilizing ecosystems. If the plant doesn’t spread by seed, it can regenerate from root fragments, giving it an even more persistent presence on your land.
Prevention & Control
The best defense against common tansy is to prevent it from ever taking root on your land. Be cautious when purchasing plants for your garden, as tansy sometimes disguises itself as an innocent nursery plant. Always confirm scientific names to ensure you’re not unknowingly inviting this invader into your landscape. If you encounter tansy off your property, clean off any seeds before returning home to avoid spreading it further. A diverse and competitive range of vegetation can also help block tansy from gaining a foothold.
If tansy is already present on your land, implementing a consistent control strategy that you work on throughout the growing season is essential. Mowing before June can help prevent seed spread, while hand-pulling is another option – just be sure to wear gloves to avoid skin irritation. For longer-term control, herbicides such as aminopyralid, chlorosulfuron, and metsulfuron-methyl are effective. Always read and carefully follow the directions outlined on the herbicide label when applying herbicides.
As is the case with most weeds, the most successful control method combines different strategies, using an integrated pest management (IPM) approach. IPM focuses on using a combination of physical, biological, and chemical treatments to manage pests in a more sustainable way. For tansy, combining mowing and herbicide treatment will help reduce the plant's spread and prevent regrowth. Don’t be discouraged if tansy returns after the first round of treatment—persistence is key in the battle against this invasive species.
Dig Deeper
For more information on invasive species and native plants, please see the resources listed below.
Weed Identification
Native Species
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Agriculture