By Erin Marissa Russell
Tansy is a perennial herb that is a member of the aster plant family. It grows in clumps between three and four feet tall, with a six-inch to 10-inch spread. Its light green leaves measure between eight and 10 inches long, are toothed, and have an appearance that resembles a fern. They grow from tall brown or purple-red stems.
Tansy plants flower into disc-shaped clumps of sunny yellow blooms, with more than 300 appearing on a single plant. Flowers appear sometime between July and the fall, with the exact timing depending on the region. Tansy flowers do very well in cut floral arrangements or dried arrangements. The flowers dry easily on their own as they sit in the vase, and they maintain the color and shape they had when alive.
The fragrance of a tansy plant has been described as a mixture between camphor and rosemary, and this scent is especially aromatic when the leaves have been crushed. Tansy is used in the culinary world to flavor dishes like omelets, salads, soups, and stews. Tansy can also be used as a fabric dye, but this application was much more common the past than it is in the modern era.
Tansy will both add potassium to your garden’s soil and help to deter pest insects from the area. They also attract beneficial ladybugs, which will do even more to keep the pest insect population in check. Experts recommend tansy in companion planting setups for its ability to repel insects like blister beetles, cucumber beetles, peach tree borers, and potato beetles. Colonial cooks would hang tansy from their kitchen ceiling to ward off ants, flies, and mosquitoes. In England during the Medieval era, tansy was strewn over the floor after a feast to keep insects far from the festivities.
The herb’s long history of use in folk medicine includes treating roundworms, soothing pain associated with menstruation and other uterine pain, functioning as a diuretic, dissolving kidney stones, and promoting healthy digestion. It was mixed with wine and drunk as a remedy for surface-level injuries, inflammation, or bruises. Midwives in the Middle Ages would make tea out of tansy plants as a natural way to terminate unwelcome pregnancy. Although tansy tea was often successful in causing miscarriage, ingesting tansy also directly poisoned the pregant woman, leaving her vulnerable to the effects of poisoning we discuss in the toxicity section at the end of the article.
Tansy was even, until late in the 18th century, a part of the embalming process that helps preserve corpses and prepare them for burial, and it was quite an effective embalming agent. The University of Arkansas Extension Service reports that in the year 1668, one of Harvard College’s first presidents was buried with his body shrouded in tansy. When his corpse was unearthed, it was still perfectly preserved—an astonishing 178 years after his burial.
In the kitchen, the bitter-tasting leaves of the tansy plant are used sparingly as a flavoring for many different foods. Along with 129 other herbs, tansy has a modern function in the process behind a French liqueur called Chartreuse. In a part of England now called Cumbria, tansy puddings served with rum sauce played a prominent role in the annual Easter Monday celebrations.
As part of Jewish tradition, sweet-tasting tansy cakes simply called “tansies” (imagine something like a cross between a green omelet and a pancake) are prepared during the Easter season. Fresh green tansy leaves are crushed and pummelled until they turn into juice, then the juice is added to the batter for the pastries. Passover tansies were initially flavored solely with the juice of the tansy plant, but over the years, recipes have expanded to include tansy along with feverfew, parsley, and violet flowers.
Varieties of Tansy
Common Tansy (Tanacetum vulgare)
Common tansy, often simply referred to as “tansy,” is the herbal perennial variety of the plant. Alternate names for common tansy include: bitter buttons, cow bitter, garden tansy, and golden buttons.
Curly Tansy (Tanacetum crispum)
Curly tansy, also called fernleaf tansy, is a better option for garden planting than common tansy is. The plant is broadly considered more attractive, though smaller than common tansy with a mature height of two and a half feet. It also doesn’t spread quite as fast as common tansy does, and its foliage has a lacier silhouette.
Isla Gold Tansy (Tanacetum vulgare)
Isla Gold tansy is a variety of common tansy that is the one you’ll most often find for sale in nurseries and garden centers. It is a bit smaller than a standard common tansy plant, and its foliage is golden yellow when it appears in the spring. As the season progresses, Isla Gold tansy’s leaves darken, finally ending up with a lime green coloring at the end of the season.
Tansy Ragwort (Seneca jacobaea)
There is a similar plant called tansy ragwort that can be discerned from common tansy by crushing the foliage. The crushed leaves of common tansy will have a pungent, noticeable aroma, whereas the tansy ragwort plant does not produce a scent at all. Tansy ragwort is a winter annual, biennial, or short-lived perennial plant that originated in Asia, Europe, and north Africa. Tansy ragwort especially acts like a perennial when its natural growth cycle is interrupted or disturbed, such as when the plants are mowed down. It grows to an average mature height of around four feet tall, and like common tansy, produces yellow flowers. Other terms for tansy ragwort include staggerwort and stinking Willie.
In addition to often being mixed up with common tansy, tansy ragwort plants are also frequently mistaken for Common St. Johnswort (Hypericum perforatum). Though it’s easy to get these two plants confused, it’s very important for gardeners to be able to accurately tell the difference. That’s because, like common tansy, tansy ragwort is considered an invasive weed in many areas—not to mention, tansy ragwort is quite toxic.
Because of how serious the poisoning response can be if tansy ragwort is consumed, it’s vital for gardeners and anyone living where tansy ragwort grows who has children or pets to know tansy ragwort if plants spring up on their property so they can remove them immediately. Tansy ragwort is fatal if ingested by cows or horses because it causes liver damage that cannot be reversed.
Not only should gardeners be able to identify tansy ragwort, it’s also crucial that they’re able to distinguish this toxic herb from the lookalike common St. Johnswort, which people may intend to consume. Here’s how you can tell tansy ragwort and common St. Johnswort apart: the foliage of tansy ragwort is ruffled and larger than that of common St. Johnswort, which has smaller leaves—but it has more of them. Another hint is to check the flowers. Each tansy ragwort flower will have 13 petals, while the blossoms of common St. Johnswort plants have five petals each.
Growing Conditions for Tansy
USDA Hardiness Zones 4 through 8 (and can sometimes be marginally hardy in Zone 3). The plants can be overwintered at temperatures down to -40 degrees Fahrenheit (-40 degrees Celsius). However, tansy plants do not tolerate extremely hot weather for long periods of time.
Full sun is needed to keep tansy happy, so make sure your tansy plants get at least six hours of sunshine each day. Partial shade will suffice as long as six hours of sun are provided, though plants that grow in full sun will have more flowers than those growing in partial shade.
Tansy grows well in soil that is somewhat dry, fertile, and drains well. As long as the soil has these traits, tansy plants will grow in a variety of soil types and in pH levels ranging from 4.8 to 7.5.
Tansy tolerates drought quite well once plants are well established. It can be aggressive and is considered an invasive plant in some areas; tansy spreads under the ground via rhizomes. Growing tansy is against the rules in Colorado, Minnesota, Montana, Wyoming, parts of Washington state,in the United States, and in Canada, it is prohibited in the provinces of Alberta and British Columbia.
How to Plant Tansy
Check before planting tansy to make sure that it is not prohibited in your region as an invasive weed. Once you get the all-clear, you may wish to consider growing tansy in a container or even indoors to minimize its spread. A tansy plant can get out of control fairly quickly between the multiplication of its rhizomes underground and tansy’s ability to self-seed on the surface of the soil.
Gardeners often begin with a tansy plant they’ve purchased at a garden center or nursery. If tansy is common in your region, you may be able to find a wild plant that you can dig up to put into your garden. If you do, however, make 100 percent sure that the plant and the soil it’s growing in do not carry disease. To be extra careful, you may choose to quarantine the plant and observe it a while to verify that it’s healthy before introducing it to its permanent home in your garden.
Another option is to plant your own tansy from seed. Unless you have some seriously high-volume plans for your tansy plants, it’s recommended to start with one plant due to tansy’s tendency to spread aggressively. You may consider planting your tansy in a spot where you can mow around it to help keep it under control.
Care for Tansy
Tansy is so easy to grow and care for that it is practically a weed. In fact, it is prohibited in certain areas for gardeners to cultivate tansy. (We’ve listed these areas in the section on growing conditions farther up the page.) If you choose to grow tansy in your garden, make sure to trim faded flowers off so that the plant will not self-seed. You’ll have enough trouble keeping up with its aggressive spread from the underground rhizomes.
If the plant grows very tall and spindly, the plants may require staking to provide them with some support. You can keep the tansy plants smaller and more compact by trimming them back every once in a while. Make your first pruning session early in the summer, and cut the plant all the way back to the ground. This will force new growth to emanate from the rhizomes under the surface of the soil.
You can also cut tansy back again late in the summer when the foliage starts to show signs of damage from the heat. If you do prune your tansy back at the end of the summer, you’ll get a brand new plant in the fall, and in especially warm areas, the plant may even bloom again.
How to Propagate Tansy
Propagation methods for tansy plants include separation, division, and propagation by seed. Because tansy tends to multiply on its own so effectively, propagation is not normally a concern.
Divide in spring, finding places for your largest tansy specimens in the outdoor garden. Small divisions can be planted in containers and grown indoors through the winter until they are better established and ready to move into the outdoor garden.
Garden Pests and Diseases of Tansy
Tansy is generally a healthy and vigorous plant that’s unbothered by infestation or illness. When it does have problems, they’re likely to be with leaf spot, mildew, or spider mites, none of which are very serious.
These delicate herbs with their pretty flowers and dainty-sounding name may seem like precious little plants, but tansy is actually poisonous to animals and humans alike. Tansy plants emit a juice or sap that can irritate skin and cause dermatitis responses. Dermatitis is simply a catch-all term for skin irritation, and it can manifest with uncomfortable symptoms like blistering, crusting, dry skin, flaking skin, itching, oozing, redness, swelling, or a rash in the affected area. However troublesome these reactions can be, skin reactions to tansy are merely superficial, cosmetic responses. Dermatitis is not nearly as serious as some of the other possible consequences of consuming tansy.
The sap of tansy plants contains a compound called thujone, which can cause convulsions as well as liver and brain damage if it is ingested in large amounts. Although tansy plants are rarely consumed by livestock because of their pungent aroma, tansy can be poisonous if it is eaten, especially in large quantities. Tansy is toxic to both humans and pets, especially cats, so if you are growing this plant, keep it well out of reach of young children or pets and the areas where they play.