Lacy phacelia
Also known as
Purple tansy, Tansy-leaf phacelia, Bee's friend, Lacy scorpionweed
Keep this plant’s care guide close at hand.
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Phacelia tanacetifolia is a fast-growing annual wildflower in the borage family prized for its exceptional nectar and pollen production. Ferny, deeply cut leaves resemble tansy, giving rise to the species name, while showy lavender to violet flowers unfurl from coiled, scorpion-like cymes over several weeks. Typically 30–90 cm tall, it establishes quickly and begins flowering about 6–8 weeks after sowing, attracting honeybees, bumblebees, solitary bees, hoverflies, and other beneficial insects. Widely used as a cover crop and green manure, it suppresses weeds, improves soil structure, and scavenges residual nutrients with its fibrous root system. It thrives in well-drained soils and sunny, temperate conditions, tolerating light frost yet disliking waterlogging and extreme heat. Although commonly cultivated across Europe and beyond, it is native to the arid and semi-arid Southwest of the United States and northern Mexico. Plants may self-seed lightly if allowed to mature seed.
Taxonomy
Properties & Requirements
How to care for Lacy phacelia
Water
Keep soil evenly moist from sowing through early establishment, watering lightly but frequently until seedlings are 5–8 cm tall. Thereafter, water deeply and less often, allowing the top 2–3 cm of soil to dry between waterings. In most climates, 15–25 mm of water per week (rain plus irrigation) suffices; increase slightly on sandy soils, decrease on clay. Avoid waterlogging, which stunts roots and invites rot. Container-grown plants dry faster—check daily in warm weather and ensure excellent drainage.
Light
Provide full sun for the strongest, nectar-rich bloom—aim for at least 6–8 hours of direct light daily. Plants tolerate very light or high, filtered shade, but flowering and pollinator activity will diminish. In hot inland climates, brief afternoon shade can reduce stress and extend the bloom period. Indoors, light levels are generally inadequate and pollination benefits are lost; this species is best grown outdoors in open, sunny beds, borders, meadows, or as cover crop strips.
Nutrients
As a cover crop or pollinator strip, lacy phacelia usually needs no fertilizer in average garden soil. On poor sites, incorporate well-rotted compost or apply a low to moderate rate of balanced fertilizer (e.g., 5-5-5) at or just before sowing. Avoid high nitrogen, which favors excessive foliage at the expense of blooms and nectar. In containers, use a light, diluted (quarter-strength) balanced feed every 3–4 weeks if growth pales. Fertilize moist soil and avoid feeding during heat or drought stress.
Temperature
A cool-season annual, lacy phacelia germinates best at 8–20°C and grows vigorously between 10–25°C. It tolerates light frosts (approximately −3°C) once established, but hard freezes can kill plants. Extended heat above about 30°C reduces flowering and nectar production; provide afternoon shade and steady moisture in hot climates. In temperate regions, sow early spring to early summer, or late summer for autumn bloom before frost. Not suited to hot, humid summers without good airflow and regular irrigation.
