Germination temperature
Sow outdoors when soil is above 10 °C (50 °F); indoors about 15 °C (59 °F) works well.
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Borage is a fast annual herb with edible blue star-shaped flowers that bees love. Its large seed is easy to sow directly; the main points are covering the seed, giving plants room, and deciding whether you want it to self-seed.
Sow outdoors when soil is above 10 °C (50 °F); indoors about 15 °C (59 °F) works well.
1.25-2.5 cm (1/2-1 in), deeper in dry soil.
7-14 days.
Not needed for germination; cover the seed. Full sun to light shade for growth.
None. Cold stratification is not needed.
Direct sow is best; young seedlings can be moved while small.
Use fully ripe seed: ripe borage seed is hard and black, about 16 g per 1,000 seeds. In a germination study, seed maturity was the main factor in germination; mature, dark seed germinated better and gave more vigorous seedlings than pale, immature seed.
Not needed. The seed takes up water without treatment.
Not needed. In the same study, stratification reduced germination, and gibberellic acid did not increase it.
Not needed. Sow into moist soil and keep it moist until emergence.
Field sowing is recommended once temperatures are above 10 °C (50 °F); for indoor sowing the RHS suggests about 15 °C (59 °F). In the Indian plains sow in the cool season after the monsoon, not into hot summer soil; in hill areas and temperate climates sow in spring.
Cover with 1.25-2.5 cm (1/2-1 in) of soil, at the deeper end in dry soil. A trial of 1-4 cm depths found germination percentage did not depend on depth, but shallower sowing emerged faster.
Any well-drained soil, pH about 6-8. Borage grows shorter in dry or poor soil and dislikes waterlogging.
Keep the seedbed evenly moist until seedlings appear. Borage is drought sensitive, so water young plants in dry spells.
Borage does not need light to germinate, so cover the seed fully. Seed catalogues often say darkness helps; covering the seed meets that either way.
Usually 7-14 days, with about 75% germination for good seed. Cold soil slows it down.
Borage is best sown where it will grow. If you start it in pots, plant out as soon as seedlings are large enough to handle, before the roots fill the pot, after a few days of hardening off.
Space plants about 40-50 cm (15-20 in) apart, or grow one plant per 30 cm (12 in) pot. Plants reach 50-70 cm (20-28 in) and start flowering in summer; a field crop is ready for seed harvest in about 100 days.
Cause: powdery mildew, usually after flowering. Fix: water at the base, keep plants spaced, and pull and compost affected plants once they finish flowering.
Cause: borage leaves are large and soft and are easily damaged by wind, insects and disease as the season goes on. Fix: grow it in a sheltered spot and harvest leaves early in the season, when quality is best.
Cause: aphids, which also colonise borage grown as a field crop. Fix: wash them off with a jet of water or pinch out heavily infested tips; check plants weekly in spring.
Cause: borage needs insect pollination, flowers over a long period and drops ripe seed (shattering). Fix: grow near other bee plants, and collect ripe black seed every few days rather than in a single harvest.
Borage self-seeds readily. If you want it to return, leave a few plants to drop seed; if not, pull plants up after flowering.
Spring-sown plants often look tired by late summer, but self-sown or later-sown seedlings flower again from early autumn.
Leaves and stems are bristly, and fresh leaves can cause contact dermatitis in sensitive people.
Pick newly opened flowers for salads and drinks. Leaves, stems, flowers and seed are traditionally harvested when the plant is in flower and the first seed is forming.
Sow Deodar borage (starflower) seeds for edible flowers and a bee-friendly garden.
It does not need light, and the usual advice is to cover it with 1.25-2.5 cm (1/2-1 in) of soil. Covering the seed keeps it moist and dark, which suits it.
Yes, while seedlings are small. Direct sowing is simpler and avoids disturbing the roots of older plants.
Common borage is an annual, but it self-seeds so readily that new plants usually appear in the same place the next season.