February–March for seed-grown onionsSow lightly in modules or a seed tray and grow on steadily.
- Germination and temperature
- Germinate under cover, then grow on in good light without excessive warmth.
- After emergence
- Give seedlings light immediately after emergence. A dark loft needs suitable grow lights; warmth alone is insufficient. Ventilate and keep the compost moist without saturating it.
- Pricking out and potting on
- Sow in modules or a seed tray. Move young plants with their root ball according to cultivar guidance; a small group of spring onions can stay together.
- Hardening off and planting out
- Gradually acclimatise indoor-raised plants to sun, wind and outdoor temperatures; shelter them again on cold nights. Plant out sturdy young onions at suitable final spacing. Seed-grown onions are plants raised from seed; onion sets are planted directly.
Onion sets and seed-grown onions are different starting routes. Bunching and spring onions are generally harvested young.
Sources and use
RHS · uien ↗Britse teeltrichtlijn voor een gematigd klimaat; de genoemde perioden zijn richtlijnen voor Nederland en Vlaanderen.
De Bolster · Bosui en stengelui telen ↗Nederlandse producent of teeltbron; de rasinstructie blijft leidend.
Royal Horticultural Society · RHS — stengelui kweken ↗Soort- of productgebonden bron; buitenlandse perioden zijn geen vaste Nederlandse zaaidatum.
Guideline periods for the Netherlands and Flanders. Check the variety, available light, soil and measured temperatures. Greenhouse heating does not guarantee enough winter light.