The Aggressive Herb That Can Take Over Your Garden If You Aren't Careful

Growing an herb garden is the perfect way to bring more pollinators to your yard — and one that doesn't require much effort. While there are herbs that can be difficult to grow, there are also plenty of varieties that thrive and grow well with little maintenance. However, gardeners should be wary of herbs that grow rapidly, as they could spread aggressively and take over the rest of your garden. One such aromatic, fast-growing herb is costmary (Tanacetum balsamita), sometimes known as Bible leaf, Sweet Mary, or Bible plant.

People enjoy growing costmary because of its fragrance, which is minty and balsamic. It's a popular herb to use in salads and has even been used to flavor beer. A 2022 study published in the journal Plants (via the National Library of Medicine) noted that costmary has also been used in the past as an alternative medicine to aid digestion, relieve pain, and treat a number of ailments. The nickname 'Bible leaf' comes from the herb's leaves, which are very long and purportedly make good bookmarks. Costmary is a perennial that can grow between 2 and 3 feet tall and thrives in USDA hardiness zones 4 to 8. And thanks to the way it spreads, this herb can quickly invade large portions of your yard if you don't take precautions. 

Costmary is not considered invasive, but it does grow aggressively. The biggest issue with this plant is its rhizomatous root system, which allows it to spread quickly and overwhelm its neighbors in the garden. One of the easiest ways to deter costmary from being so aggressive is to grow it in containers and simply eliminate the roots' ability to spread. If growing costmary in-ground, consider giving it enough space in its own bed, where it won't crowd out other plants. If you're thinking of growing companion plants in the garden, costmary might work best near nasturtiums for a pop of color or behind herbs like oregano, sage, or thyme.

As long as you have a strategy for containing its growth, don't be afraid to include costmary in your garden. Especially if you're growing a medieval garden, perennial garden, or a hedge border, costmary will fit in perfectly. In addition to being aromatic and delicious, costmary can also produce cute, yellow button-shaped flowers that spruce up any garden area. This herb enjoys full sun or partial shade and well-drained soil. To keep the plant from getting too leggy, prune it back after it's done flowering for the season. Costmary is extremely difficult to grow from seed, so your best bet is to purchase clippings at a nursery or garden center.