How to Identify and Remove Common Tansy

Tansy is an aromatic perennial easily identified by its dark green fern-like foliage with golden button-like flower clusters on stems up to 5 feet. Common tansy was an important medicinal herb in Europe and was brought to the New World by American colonists and used as an ornamental plant. Today, it is considered invasive in North America.

The plant has naturalized into surrounding areas, displacing native plant communities, and has led to a decline in wildlife habitat and water quality. Common tansy is a prolific seed producer, so deadheading the flowers before the plant goes into seed will help you control its spread. If you have common tansy growing on your property, it is best to eliminate it. The leaves of the common tansy are toxic to humans, cows, and horses.

Invasiveness of Common Tansy

Although common tansy prefers moist, humus-rich soils, it can grow in a wide range of soils, including dry, poor, and disturbed soils. It reproduces fast by seeds and rhizomatous roots, and once established, it forms a dense cover, choking out native vegetation that serves as food and shelter for native wildlife, thus affecting species diversity. One plant produces more than 2,000 seeds. Most of the seeds drop near the plant but they can also be dispersed by wind and water.

Because common tansy grows in dense patches, it can clog drainage ditches. It also has a detrimental effect on pastures, making them unfit for livestock, as common tansy is toxic to horses and cows. Because it grows so densely, the production of forage plants that livestock can feed on is greatly reduced.

How Does Common Tansy Look Like

Tansy has three to six vertical stems that are brown to reddish-brown or purplish-red at the base. The plant has green, fern-like or feathery alternate leaves. When crushed, the leaves give off a pungent camphor-like odor, which makes it easy to identify the plant. The heavily scented leaves of common tansy act as insect repellent so the plant is not vulnerable to pests or disease–another factor that favors its survival and uncontrolled spreading.

From July to September, common tansy has bright golden or yellow button-like blooms, 1/4 to 1/2 inch wide, that grow in flat-topped flower clusters up to 4 inches wide. The flowers turn into tiny dark brown seed heads in the late summer to fall, from which the plant reseeds itself prolifically.

How to Get Rid of Common Tansy

Individual plants or small patches of common tansy can be removed manually but they require a shovel since the roots are deep. It is also crucial to remove all of the roots, as the plant will regrow from root fragments. Make sure to wear gloves when touching the plants, as the leaves can cause contact dermatitis.

A broad-spectrum herbicide should only be used if the infestation is so large that it cannot be managed by manual removal. When using chemical herbicides. target the plants to be removed, avoid drifting, and wear protective clothing, gloves, and goggles. Mowing an infestation can be an effective way of weakening the plants before applying herbicide to the regrowth. It also requires less herbicide than when treating full-sized plants.

How to Prevent Common Tansy From Spreading

Whichever removal method you use, get rid of the plants before they set seed, either before or during the flowering period in the summer. If you remove common tansy in the late summer or fall after the seed heads have already developed, new plants will germinate the next year.