The Dirt | Weed of the Month July 2026 | Common tansy (Tanacetum vulgare)

Info on common tansy: a noxious weed in Oregon, toxic to humans. It has feathery leaves, yellow flowers, and requires management.
A cluster of bright yellow flowers with a feathery green stem and leaves, surrounded by lush green foliage.
Common tansy (Tanacetum vulgare) plant. Photo credit: Bruce N. Newhouse.
A cluster of bright yellow, round flowers with a textured appearance against a dark background.
Common tansy (T. vulgare) floret structure up close. Photo credit: Gabriel E. Campbell.
A green plant with feathery leaves and bright yellow, round flowers, with a bee gathering nectar.
Common tansy (T. vulgare) plant with noticeably dissected leaves. Photo credit: Bruce N. Newhouse.
A cluster of tall green plants with feathery leaves and bright yellow flowers, set against a natural backdrop.
Common tansy (T. vulgare) monoculture. Photo credit: Gabriel E Campbell.
A cluster of bright yellow flowers with thin, spiky petals growing amidst green foliage.
Tansy ragwort (Senecio jacobaea) for comparison. Photo credit: unknown.
The image features a green, finely divided leaf, possibly from a plant such as a type of herb or ornamental foliage.
Tansy ragwort (S. jacobaea) leaves for comparison. Photo credit: Gerald D. Carr.
A cluster of bright yellow flowers with a feathery green stem and leaves, surrounded by lush green foliage.
A cluster of bright yellow, round flowers with a textured appearance against a dark background.
A green plant with feathery leaves and bright yellow, round flowers, with a bee gathering nectar.
A cluster of tall green plants with feathery leaves and bright yellow flowers, set against a natural backdrop.
A cluster of bright yellow flowers with thin, spiky petals growing amidst green foliage.
The image features a green, finely divided leaf, possibly from a plant such as a type of herb or ornamental foliage.

Our July Weed of the Month is Common tansy (Tanacetum vulgare). Though it shares "tansy" in the name, it is a different species than the widely known Tansy ragwort (Senecio jacobaea).  Common tansy (T. vulagre)  inhabits similar habitats as tansy ragwort: roadsides, ditches, agricultural pasures. It also inhabits riparian areas such as river banks.

Common tansy's button-like flowers appear later in the season (mid to late July-September) compared to the noticeable ray flowers of tansy ragwort (late May/early June-September). Common tansy leaves are deep green in color and deeply dissected, almost giving the vegetation a feathery appearance. In contrast, tansy ragwort's leaves are irregularly lobed, crinkly-compact, and smaller in size.

Though common tansy is not recognized as a noxious weed in the state of Oregon, it is a problematic species to control. It is unpalatable to cattle and toxic if eaten by humans or animals. It grows from a deep root system and produces prolific seeds. Mowing this plant low to the ground in summer or manually pulling it out of the ground are effective management stratgies for small infestations. For larger infestations, chemical control may be necessary. 

Keep Reading

  1. Oregon Flora - Common Tansy
  2. Stutz,Sonja and McClay,Alec S. and De Clerck-Floate,Rosemarie A., 9781800623279.0060, CABI Books, doi:10.1079/9781800623279.0060, (569–574), CABI, Tanacetum vulgare L., Common Tansy / Tanaisie commune (Asteraceae), (2024)