The blue tansy plant, Tanacetum annuum, offers a unique aesthetic to any garden. It is noted for its bright yellow, button-like flowers and delicate, feathery foliage.
Understanding the Blue Tansy Plant
Tanacetum annuum, commonly known as blue tansy, is a flowering plant native to the Mediterranean region, primarily Morocco. It typically grows 1 to 3 feet tall, displaying finely divided, fern-like leaves and numerous small, bright yellow, button-shaped flowers in clusters. These flowers bloom from mid-summer into early fall.
Despite the plant’s yellow flowers, its essential oil is famously blue. This occurs during the steam distillation process, where matricin, a chemical compound naturally present in the plant, reacts with hot water vapor to form chamazulene. Chamazulene is responsible for the oil’s intense indigo-to-cerulean hue, which gives blue tansy its name.
Cultivating Blue Tansy
Blue tansy thrives in conditions mimicking its native Mediterranean environment. It prefers full sun (at least six hours daily) for optimal growth, though it can tolerate partial shade. Adequate sunlight encourages abundant flowering and robust plant development.
Well-draining soil is important, as blue tansy does not tolerate soggy conditions that can lead to root rot. A sandy loam soil with a slightly acidic to neutral pH (5.0-7.5) is ideal. Amending the soil with compost improves fertility and drainage, supporting healthier plant growth.
Once established, blue tansy is drought-tolerant, but consistent watering benefits it during its active growing season. Water deeply when the top inch or two of soil feels dry, allowing the soil to dry out between waterings. More frequent watering may be necessary during hot periods to maintain plant vigor.
Blue tansy is hardy in USDA zones 4 through 8. It prefers moderate temperatures and does not thrive in prolonged, intense heat or extreme cold. It adapts to various humidity conditions.
While blue tansy can grow in less fertile soils, an annual topdressing of compost or a light application of a balanced organic fertilizer every 4-6 weeks during the growing season promotes more vigorous growth. Avoid over-fertilization, as it can lead to excessive foliage at the expense of flowers. Propagation occurs through seeds, which often require cold stratification for better germination, or by taking cuttings from new growth in late spring or early summer. Pruning maintains the plant’s shape and encourages bushier growth; deadhead spent flowers to promote continuous blooming and prevent prolific self-seeding.
Harvesting and Uses of Blue Tansy
Harvesting blue tansy involves collecting the flowering tops when they are in full bloom, usually from mid-July through September. Leaves can also be gathered throughout the growing season. Use clean, sharp shears to cut the stems.
The primary commercial use of blue tansy is its essential oil, highly valued in aromatherapy and skincare. Home growers cannot extract this essential oil themselves, as it requires specialized distillation equipment. While the plant has limited direct uses for the average gardener beyond ornamental appeal, its harvested material can be added to compost piles to enrich soil.
Important Considerations and Distinctions
Differentiate Tanacetum annuum (blue tansy) from Tanacetum vulgare (common tansy). Common tansy is a different species that can be toxic if ingested, containing compounds like thujone not present in blue tansy essential oil. Common tansy also has a strong, pungent odor and can cause skin irritation upon contact.
While blue tansy essential oil is often used topically when properly diluted, the plant itself should not be consumed. Ingesting parts of the blue tansy plant may cause adverse reactions. Handle the plant with caution and keep it away from pets and young children to prevent accidental ingestion or skin irritation.