Germination temperature
Cool: most species germinate after a winter chill, as soil warms in spring.
Visit deodar-seeds.in Bulb growing guide
Ornamental alliums, the drumstick and globe-flowered onions, can be raised from seed sown fresh or after cold storage and left outdoors over winter. Most germinate within 12 weeks of the cold, but seedlings need several years to reach flowering size. For culinary onions see our onion growing guide.
Cool: most species germinate after a winter chill, as soil warms in spring.
Surface-sown, covered with about 5 mm (0.2 in) of grit.
Most within 12 weeks; some species take longer.
Seed trays in shade outdoors; plants in full sun.
Sow fresh, or store in the fridge and sow in spring; a winter chill helps.
Sow in trays, grow on as small bulbs, plant out in autumn.
RHS advises sowing ripe allium seed as soon as possible. If you cannot sow at once, keep the seed dry in a sealed container in the refrigerator and sow in spring.
Not needed. Allium seed dormancy is broken by cold and moisture, not by damaging the coat.
Usually helpful. In a Utah State University study of three wild Allium species, all germinated better after moist chilling at 3 °C (37 °F). The simplest method is to sow in autumn or winter and leave the tray outdoors; where winters are mild, put the sown tray in a plastic bag in the refrigerator for several weeks before bringing it out.
Not needed. Seeds take up water from the moist compost during the chilling period.
Alliums germinate in cool conditions after the chill; the Utah study germinated chilled seed at only 8 °C (46 °F). Do not try to force them in heat: warm, humid trays mainly grow moss and mould.
Sow thinly on the surface and cover with about 5 mm (0.2 in) of grit, as RHS recommends.
Gritty, peat-free seed compost that drains freely. Wet, airless compost rots seed and young bulbs.
Keep the compost just moist through winter; protect trays from heavy rain so they do not stay waterlogged.
Stand trays outside in a shady spot while they chill and germinate; move seedlings into good light once they are up.
Most should germinate within 12 weeks. Seedlings look like single grass blades. Keep the tray for a second season, as some species come up only after another winter.
Leave seedlings in the tray for their first season. When the leaves yellow and die down, keep the compost barely moist; the tiny bulbs are resting, not dead.
When dormant, tip out the tray and pot the small bulbs a few to a pot in gritty compost, or line them out in a nursery row, about 2.5 cm (1 in) apart.
Plant bulbs out in early to mid autumn at about four times their diameter, small species 7.5-10 cm (3-4 in) apart and tall ones at least 20 cm (8 in) apart. Seed-raised plants take several years to reach flowering size.
Cause: no cold period, or old seed. Fix: sow fresh seed in autumn and leave the tray outdoors over winter, or chill it in the refrigerator, and keep it a second year.
Cause: heavy, waterlogged soil or compost. Fix: use gritty, free-draining mix, raised beds and full sun; avoid freshly manured soil.
Cause: normal; allium leaves die down at flowering time. Fix: plant among other perennials that hide the foliage; dying leaves can be removed safely.
Cause: allium leaf miner, onion fly, or slugs and snails. Fix: avoid ground where onions have grown, cover young plants with fine mesh where leaf miner is present and control slugs.
Cause: onion white rot, shared with culinary onions. Fix: lift and destroy affected bulbs and do not replant alliums in that ground.
Alliums thrive in full sun and are drought tolerant once established. Avoid cold, exposed or waterlogged sites; on the Indian plains this means a well-drained raised bed and protection from monsoon waterlogging.
Tall border alliums need a sheltered spot so their flower stems are not blown over.
Seed from hybrid alliums does not come true; seedlings may differ in colour and shape from the parent.
Mature clumps can be lifted after the leaves die back to detach offsets. Species such as A. sphaerocephalon and A. roseum also form small aerial bulbils, which are planted about 2.5 cm (1 in) apart and grown on for several years like seedlings.
Sow ornamental allium seed in autumn and let winter cold do the work.
Several years. Seedlings first build up a bulb large enough to flower, so plant some bulbs alongside if you want flowers sooner.
Most species germinate much better after a cold, moist winter period. Sow in autumn and leave the tray outdoors, or chill it in the refrigerator where winters are mild.
No. It covers ornamental alliums grown for their flowers. For bulb onions use our onion growing guide.