How to Grow and Care for the Blue Tansy Plant

Blue tansy (Tanacetum annuum), sometimes called Moroccan chamomile, is an annual herb native to the Mediterranean basin. This plant is recognized for the deep blue essential oil extracted from it. While it grows wild, cultivation is increasing to meet demand.

Identifying the Blue Tansy Plant

Correctly identifying Tanacetum annuum is important due to its resemblance to a toxic relative. The plant features delicate, fern-like foliage covered in a fine white fuzz, giving it a soft, feathery appearance. Its growth habit is bushy and compact.

The flowers are small, yellow, and button-like, growing in clusters on slender stems. A different plant, common tansy (Tanacetum vulgare), has similar yellow button-like flowers but is a much larger, more aggressive plant that is toxic. Always verify the species by looking for the fine, downy leaves of Tanacetum annuum to ensure you have the correct plant.

How to Grow Blue Tansy

To cultivate blue tansy, replicate its native Mediterranean conditions. The plant thrives in full sun, needing at least six to eight hours of direct sunlight daily. As an annual, its seeds should be sown in the spring after the danger of frost has passed.

Blue tansy requires well-draining soil to prevent root issues; sandy or loamy soils are ideal. Before planting, clear weeds and loosen the soil. Sow seeds directly into the garden bed by pressing them lightly into the surface, or for seedlings, use a hole slightly larger than the root ball. Space plants about 18 inches apart to allow for mature growth.

Once established, Tanacetum annuum is moderately drought-tolerant but requires consistent moisture during dry periods. Avoid overwatering by checking that the top layer of soil is slightly dry before watering again. Keep an eye out for common pests like aphids and deadhead spent flowers to encourage a longer blooming season.

Harvesting and Uses

The primary use of blue tansy is for its essential oil. The flowers and stems are harvested when the plant is in full bloom, which occurs from late spring into summer. Harvesting involves cutting the above-ground portions of the plant for processing.

Though the flowers are yellow, the essential oil is a deep blue. This color change is the result of a chemical reaction during steam distillation. A compound in the plant called chamazulene is released and, when heated, transforms to give the oil its indigo hue. Besides oil production, the flowers can be used in dried floral arrangements.

Safety Considerations

The raw Tanacetum annuum plant should be handled with care. It contains a compound called thujone, which is toxic if ingested, so it is not recommended to consume any part of the plant. Be mindful of this in areas accessible to pets or small children.

During steam distillation, the chemical profile of the final oil is altered, and toxic compounds like thujone are removed or significantly reduced. The essential oil itself should never be ingested and must be diluted with a carrier oil before being applied to the skin. When purchasing oils, confirm the botanical name is Tanacetum annuum to avoid the toxic common tansy.