How to Grow Costmary Herb (Tanacetum balsamita)

By Matt Gibson

Costmary is a delightfully fragrant and ornamental perennial herb that smells and tastes like spearmint with a hint of eucalyptus. It’s long, thin, serrated leaves are rounded, but narrow, and greenish-grey. In the spring and summer, it displays clusters of small, white or yellow disc-shaped flowers that are very reminiscent of tansies. Considered a hedge, bush, or shrub, the costmary plant is a bushy, low-growing plant that grows between one to two feet tall and wide. In cold weather regions, expect the costmary plant to die out in the winter and re-sprout in the spring.

An Asian native from the daisy family, costmary is hardy to USDA zones four through eight. The herb was introduced to England in the 1600’s and quickly became a culinary staple. Though today, the herb has practically disappeared from Europe, costmary is still very popular in southwest Asia. Costmary has a history of medicinal use, usually to bring on menstruation, or for other women’s health issues. Pregnant women should avoid ingesting costmary, as it is known to cause miscarriages.

Today, costmary is often grown as an ornamental plant, and is also still cultivated and used as a culinary herb in many areas of the world. Its leaves can be used to flavor teas, soups, stews, and casseroles. The leaves can be used fresh or dried. Dried herbs are usually used as a cupboard spice, while the fresh leaves are often added to salads, fruit salads, and wraps, for a fresh minty flavor. 

Costmary is a plant with many monikers. There is some debate over whether Costmary was named after the Virgin Mary, or after Mary Magdalene, but either way, it derives several of its common names from a Mary from biblical times. The name bible plant was bestowed upon costmary because it was commonly used as a bookmark for bible readers, and the highly-fragrant leaves were also used like smelling salts to keep tired congregation members from catching some involuntary z’s during especially long-winded sermons. 

Before the hops craze, brewmasters used a number of herbs to invigorate their beer and ale with a spicy burst of flavor. For decades, costmary was a common flavoring agent for breweries, adding a slightly spicy, minty flavor, earning it the nickname Alecost, or Alecoast, and Sweet Tongue. Costmary is also known as Sweet Mary, Mary’s Mint, Costmarie, Balsamita, Mace, Balsam Herb, and Mint Geranium, though it is not related to either mint, or geranium. If you have ever grown tansies or feverfew, costmary is a cousin to both of these flowering plants, and shares a similar set of growing requirements and care instructions

Varieties of Costmary

Tanacetum balsamita is the only known variety of costmary. Unlike many other plants that have been duplicated by horticulturalists, costmary declined in popularity before genetic breeding became popular. 

Growing Conditions for Costmary

Costmary plants enjoy full sunlight exposure. They will tolerate partial shade, but blooming is significantly lower in shaded locations. Costmary is not particular about the soil it is grown in. It will adapt to and thrive in any medium, including dry soils, clay or sand soils, and even depleted soils. Costmary grows well in an herb garden with short herb plants which won’t block out the sunlight that it needs to thrive, such as sage, thyme, and oregano. 

How to Plant Costmary

Growing costmary from seed is next to impossible to grow from seed. Instead, purchase young costmary plants at your local nursery or greenhouse, or, if you have a friend who has an established costmary plant, ask them to share divisions with you. 

Pick a full sun location. Full sun is preferred but partial shade will suffice as well, just avoid full shade locations as the flowering herb will refuse to produce blooms if it does not get enough direct sunlight exposure. Once you have a location picked out, amend the soil prior to planting with plenty of compost for a humus-rich, well-drained medium. Adjust soil pH [ to fall between 6.0 and 6.7.

Transplant young costmary plants or seedlings into the garden in mid to late-spring, or set out rhizome divisions after the final spring frost has passed, spacing plants out two to three feet apart. Costmary can be overpowering, and is only needed in small quantities. For culinary use, you shouldn’t need more than one costmary plant.

When selecting companion plants for costmary, keep in mind that the herb is an invasive spreader. Its rhizome roots tend to crowd out neighboring plants, keeping them from expanding and stunting their growth. Therefore, the best companion plants for costmary are already established plants that stand up to invasives and hold their ground. Costmary plants are also known to repel moths, so it is a good idea to plant costmary near plants who are prone to attacks from moths, or plants that are susceptible to garden diseases which are commonly carried and transmitted by moths.  

Care for Costmary

Costmary plants are relatively easy to care for. They need a soil that is kept evenly and consistently slightly moist but not soggy or drenched. If you provide your costmary with a loamy, humus-rich soil that was amended with aged compost before planting, you don’t need to add any fertilizer during the growing season. 

Prune back your costmary plants so that they don’t become leggy. Cut back flowers to encourage more foliage. After the plant goes to flower, cut the whole plant back down to three to four inches above the ground. The plant will grow back in place in just a few weeks. Mature plants need to be divided once every three years to keep them healthy. 

Costmary can also be grown in containers, as long as the planters are at least 12 inches wide and 12 inches deep. In cold weather climates, costmary will wither and die to the ground during the cold season, re-sprouting in spring with vigorous new growth. Container plants should be pulled indoors, or into a climate controlled greenhouse during the winter months. 

How to Propagate Costmary

Costmary plants can be propagated by seed, division, or young stem cuttings. Division and cutting are the preferred propagation methods, however, as growing costmary from seed is notoriously difficult, perhaps even impossible. Costmary is rarely grown from seed and attempting it is discouraged. The seeds are incredibly difficult to germinate. The seeds require stratification before germination is possible, so if you are going to attempt to grow costmary from seed, stratify your seeds by storing them in the fridge for a few weeks prior to planting. 

Division is the easiest way to propagate costmary plants, and it needs to be done once every three years in order to keep the plants healthy. Division should be carried out in either spring or fall. Replant the divisions at the same depth as they were growing originally. Water well after transplanting.

Costmary can also be grown from young stem cuttings. Dip the cut ends of six to eight inch stem cuttings in a rooting hormone and place the cuttings into a high-quality, organic potting mix. Root your costmary cuttings during the spring or fall, and move them into the garden in the late spring. 

Garden Pests and Diseases of Costmary

One of the perks of growing costmary is that it is free from pest and disease issues. The loud, pungent minty aroma of the herb deters most pests and animals, and the plant is not susceptible to any serious blights or diseases. The only issue that costmary plants might face is complications due to overwatering.

Though costmary likes a consistently moist soil, it is a good idea to let a little time pass between waterings, as long as the soil doesn’t dry out completely, a little bit of time without water will help to avoid yellowing or drooping. If you notice your costmary plant drooping a bit, or the foliage starting to yellow, cut back on watering until the soil dries out a little bit. Then, reintroduce watering, slowly at first, giving the plant smaller doses of water, but more times per week for the first week, then resume your regular watering schedule. 

How to Harvest Costmary

Costmary leaves can be harvested at any time after the plant becomes established, but the oils are the most potent just before flowering. To harvest, just snip off the leaves with a sharp pair of scissors or garden shears. 

How to Store Costmary

For brief storage of fresh costmary leaves, wrap in a damp paper towel and store in a perforated plastic bag in the refrigerator to store for three to four days. Leaves should be allowed to dry out on a screen or a tray in a warm area out of the reach of direct sunlight, which should take around two weeks. For extended storage, keep dried leaves in an airtight container in a cool, dry, dark, location.  

Costmary is not one of the most popular plants in the herb garden. It used to be a regular sight in herb gardens and was actually an incredibly popular plant that was used for baking, brewing, cooking, tea making, and seasoning. Nowadays, it is much less common, both as a garden fixture, and as a kitchen ingredient. Sometime in the 1800’s, the appeal of the costmary plant lost its luster with our society, though the reasons for the decline in popularity are unknown.

Bringing costmary back into the spotlight may not be for everyone, and it may not be making a comeback anytime soon. However, that doesn’t mean it shouldn’t get a spot in your herb garden and a chance to shine in your kitchen. It may end up being one of your favorite plants once you give it a try. 

Learn More About Costmary Herb

https://www.botanical.com/botanical/mgmh/c/costm107.html

https://www.gardeningknowhow.com/edible/herbs/costmary/costmary-plants-in-gardens.htm

https://harvesttotable.com/how-to-grow-costmary/

https://www.motherearthliving.com/plant-profile/costmary

https://plants.ces.ncsu.edu/plants/tanacetum-balsamita/

https://www.shootgardening.co.uk/plant/tanacetum-balsamita

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