Common tansy

(Tanacetum vulgare)

Erect, bushy perennial 30 cm to 1.8 meters (1 - 6 feet) tall. Forms dense patches. Introduced from Europe in the 1600s for medicinal use.

Quick Identification:

• Dark green fern-like leaves.
• Stems often purplish-red.
• Yellow, button-like flowers in a dense, flat-topped cluster.
• Leaves and flowers are aromatic when crushed.

Interesting Facts:

Has been used medicinally to expel intestinal worms, to repel insects, and to stimulate menstrual bleeding. Toxic if ingested in large quantities, but can be grazed safely by sheep and goats.

Management:

Common tansy can be mowed before flowering and seedset to eliminate seed production. This method may have to be repeated for many to eliminate re-growth from rootstocks. Some selective herbicides are effective for controlling this species.

Reproduction and Dispersal:

By seeds, creeping roots and root fragments. Spread by vehicles and equipment, infested gravel or hay, and by water.

Habitat Preference:

Disturbed areas, stream banks, riverbanks, waterways,
roadsides and fields. Prefers full sun and well-drained
soil.

Common Tansy Flowers

Common Tansy Infestation

Common Tansy Flowers

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Flowers:

Dense, flat-topped clusters of 20 to 200 yellow-orange, button-like flowers at tops of stems. Flower heads consist of disk flowers surrounded by a ring of ray flowers that lack petals. Greenish-brown bracts below the flower heads overlap in 2 to 3 rows and have papery tips.

Leaves and Stems:

Dark green, fern-like leaves are deeply divided into leaflets with toothed margins and are dotted with small pitted glands. Stems are green or purplish-red, dotted with glands and somewhat woody near the base. Several branched stems per plant. Stem leaves are alternate. The leaves have a strong odour.

Seeds:

Oblong, tan to gray, five-angled seeds, 1.5 mm long. Can produce over 50,000 seeds.

Roots:

Extensive, short, thick creeping roots, or rhizomes, with numerous lateral roots.

Impacts:

It grows at low to mid elevations in full sun in fertile, well-drained soils. Often infests stream banks, pastures, and other disturbed sites such as roadsides but can not effectively establish in frequently tilled soils. This species continues to be cultivated in gardens around the district.

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