Lacy phacelia is an annual plant known for its ease of care and rapid growth. Special care points include ensuring well-draining soil to prevent root rot and providing full sun exposure to promote vibrant blooms. Regular watering is important, but lacy phacelia is also drought-tolerant once established, easing maintenance concerns. Its simplicity in care makes it an accessible choice for gardeners of all levels.
I. Appearance and Characteristics
Phacelia tanacetifolia is a species of flowering plant in the borage family Boraginaceae, known by the common names lacy phacelia, tansy-leaf phacelia, blue tansy, purple tansy or fiddleneck (UK).
Phacelia is derived from Greek and means ‘bundle’, in reference to the clustered flowers, while tanacetifolia means ‘with leaves resembling those of Tanacetum.’
Phacelia tanacetifolia is an annual that grows erect to a maximum height near 100 cm (40 in) with none to a few branches. The wild form is glandular and coated in short stiff hairs. The leaves, 20–200 mm (1–8 in), are mostly divided into smaller leaflets which are deeply and intricately cut into toothed lobes, giving them a lacy appearance. The dense and hairy inflorescence is a one-sided curving or coiling cyme of bell-shaped flowers in shades of blue and lavender. Each flower is just under a centimeter long and has protruding whiskery stamens.
The seeds are “negatively photoblastic”, or photodormant, and will only germinate in darkness.
II. How to Grow and Care
Light and Temperature
Blue tansy grows best in full sun, but also tolerates partial afternoon shade.
It is not winter hardy and often dies at 18° degrees Fahrenheit (-8° C).
USDA Hardiness Zones 3 – 10.
Watering
Originating from arid environments, lacy phacelia has adapted to thrive with minimal moisture, exhibiting a remarkable drought tolerance. It prefers infrequent watering, aligning with its native habitat’s conditions. In cultivation, lacy phacelia should be watered once every 1-2 weeks to maintain optimal health. This plant is adept at conserving water within its tissues, allowing it to sustain periods of dryness. As an outdoor-grown species, lacy phacelia’s growth cycle is closely tied to water availability, often flourishing in the seasonal rains that punctuate its otherwise dry climate.
Fertilizing
Lacy phacelia thrives with balanced nutrition fertilizers but may benefit from high nitrogen during early growth for foliage. Fertilize every 4-6 weeks during active growth, using half the recommended strength to prevent over-fertilization. Purpose: ensures vibrant blooms and robust health. In spring and early summer, adhere to a more frequent schedule, tapering off as lacy phacelia matures. Use a slow-release formula to maintain steady nutrient provision. Avoid application during dormant winter months. Tip: Water lacy phacelia before and after fertilizing to protect roots.
Soil and Transplanting
Since purple tansy plant mainly grows in deserts, at high altitudes, in its natural habitat, it prefers gravelly or sandy soil.
It also required the soil to be dry and well-draining.
Do not plant in soil with poor drainage as the plant doesn’t grow properly in waterlogged soils.
Grooming and Maintenance
Phacelia tanacetifolia is a low-maintenance plant and doesn’t need grooming or lots of care to grow.
However, since the plant self-seeds abundantly, you would need to deadhead the plant if you want to prevent self-seeding.
Propagation
Purple tansy can only be grown from seeds.
While seeds are easy to germinate, they should be kept in darkness for at least the first 24 hours, after sowing.
Darkness is critical for the germination of lacy phacelia seeds as they are photodormant.
Also known as negatively photoblastic, photodormant seeds need darkness to germinate.
Nick or scratch the seed cost, soak them overnight and then sow the seeds directly on top of the soil in their permanent location anytime from spring to fall.
Pests and Diseases
Blue tansy is susceptible to soil-borne diseases, like Rhizoctonia solani and Sclerotinia minor.
To reduce the risk of these diseases, it is recommended to not grow tanacetifolia in rotation with the plants affected by any of these pathogens.
The plant is known and prized for its ability to attract a number of beneficial insects and pollinators, including honey bees and bumblebees.
This phacelia species also attracts hoverflies, which are highly useful biological pest control agents.
Hoverflies are highly effective for eliminating a number of pests, including aphids.
All these qualities make this herbarium species a valuable insectary plant.
III. Uses and Benefits
- Beneficial insects
Phacelia tanacetifolia is native to the Southwestern United States and northwestern Mexico. It is most common in the deserts of southern California at elevations below 1,500 m (5,000 ft), but may be occasionally found at much higher elevations.
It is used outside its native range in agriculture as a cover crop, a bee plant, an attractant for other beneficial insects, as a green manure and an ornamental plant. It is planted in vineyards and alongside crop fields, where it is valued for its long, coiling inflorescences of nectar-rich flowers which open in sequence, giving a long flowering period. It is a good insectary plant, attracting pollinators such as bumblebees and honey bees.
- Biological pest control
It is also attractive to hoverflies (family Syrphidae), which are useful as biological pest control agents because they eat aphids and other pests.
