Phacelia tanacetifolia Seeds | Phacelia
LATIN NAME: Phacelia tanacetifolia
COMMON NAME: Phacelia
Plant Profile
Phacelia is an annual of the waterleaf family from California, and it has become one of the most widely sown plants in European agriculture without most gardeners realising it is a garden plant at all. It grows sixty to one hundred and twenty centimetres tall, with deeply divided, ferny, mid-green leaves and stems that carry a dense, one-sided coil of small lavender-blue flowers, each with long, protruding stamens.
The coil is a cincinnus: it unrolls as the flowers open, so the head starts as a tight spiral and ends as a straight, feathery spike. Flowering runs for six to eight weeks from early summer and stops only with the first hard frost. The whole plant is covered in stiff, glistening hairs, which give it a grey bloom in the sun and a rough feel in the hand.
Science & Biotechnology
Phacelia is a light-requiring germinator, which is why it is broadcast on the surface rather than buried, and why a dense sowing in cold soil can fail while a shallow one succeeds. The species is grown agriculturally as a green manure, a cover crop and an insectary plant: its roots are fibrous and fast, it suppresses weeds by shading, and its flowers supply nectar and pollen at a sugar concentration that suits short-tongued bees, hoverflies and predatory wasps.
It is also used in studies of conservation biological control, because the hoverflies it attracts lay eggs whose larvae eat aphids. The plant is not frost-hardy and dies at about minus five degrees, which is part of its value: it winter-kills and leaves a mulch without becoming a weed. The hairs can cause contact dermatitis in sensitive people, and handling the plants wet is best avoided.
Uses & Benefits
Sown in a strip beside a vegetable plot, phacelia brings in pollinators and aphid predators in numbers that are visible within a fortnight, and it is one of the most reliable plants for that job. As a green manure it produces a large bulk of soft growth in ten weeks and can be dug in before it sets seed, adding organic matter and improving soil structure.
In the flower garden it is a useful filler for gaps, a good cut flower in a loose, naturalistic arrangement, and a plant that will grow in poor, dry soil where little else will. It is also one of the best plants for a bee garden in late summer, when the June flush is over and the bumblebee colonies are at their peak. It self-sows gently if a few plants are left to seed, which suits a meadow strip but not a tidy border.
Growing from Seed
Sow direct where it is to grow, from April to July, on the surface of a fine, firm seedbed and rake lightly; do not bury the seed, because it needs light to germinate. Keep the ground moist until the seedlings are up, which takes ten to fourteen days.
Thin to fifteen centimetres if the plants are crowded, though a dense stand is fine for green manure. There is no need to raise it in modules, and transplanting is a waste of time. For a succession, sow a metre-wide strip every three weeks until midsummer, and cut the plants down before the seed sets if you do not want it to self-sow, which it will do freely.
Our Take
The most useful annual you can sow for bees and soil, and it asks for nothing but a rake. Sow it once and it will find a place in the rotation every year after.
Related Reading
Gardeners who grow Phacelia often pair it with these related subjects: