Propagation guide

How to propagate Ailsa Craig Onion (Allium cepa) — step by step

Also called Exhibition onion, Ailsa Craig, Show onion.

The best way to propagate ailsa craig onion

The reliable, beginner-friendly way to propagate ailsa craig onion is seed (with cuttings or suckering as a shortcut where possible). It suits this species because of how it grows: upright-leaved annual bulb. Sow seed in January-February in heated propagator (15°C) or directly outdoors from March. Thin to 15-30 cm apart for standard bulbs or 30 cm for exhibition specimens. Can also be grown from sets (small bulbs) planted in spring or autumn.

For the wider picture of which technique suits which plant, our guide to plant propagation methods compares water, soil, leaf, division and offset propagation side by side.

Step-by-step: propagating ailsa craig onion

Start seed indoors. Sow ailsa craig onion seed into modules of fine compost 6–8 weeks before your last frost; keep at the right warmth until they germinate.
Grow on. Give bright light, pot on as roots fill the cell, and harden off over a week before they go outside.
Transplant out. Plant out only once the danger of frost has passed and the soil has warmed, at the spacing the crop needs.
Cutting shortcut. Where the plant suckers or roots from a softwood shoot, rooting a cutting clones a favourite specimen and skips the seedling stage.
Save your own seed. Let a strong, true-to-type plant set and ripen seed, then dry and store it cool and dark for next season.

The alternative method

If the main route does not suit your plant or setup, rooting a sucker / softwood cutting is the next best option for ailsa craig onion. Where the plant suckers or roots easily from a softwood shoot, a cutting clones a favourite specimen exactly and reaches a useful size faster than starting again from seed.

Timeline to roots

Realistically: seed to transplant in 4–8 weeks. These numbers assume spring or summer warmth and bright indirect light. In a cold, dark room — or in winter dormancy — the same ailsa craig onion propagation can take twice as long or stall completely, so do not panic if progress looks slow out of season. Patience beats poking: disturbing a forming root system to “check” on it is a common way to set it back.

Common failure points

Sowing or transplanting before the soil and air have genuinely warmed past the last frost.
Leggy seedlings from too little light indoors — they never fully recover.
Skipping hardening off, so transplants stall or scorch outdoors.
Saving seed from a hybrid and being surprised it does not come true.

When to do it

The best window is start indoors 6–8 weeks before last frost. Propagation is energetically expensive for a plant, and it only has the spare resources to build new roots when it is already growing actively, warm and well-lit. Out-of-season attempts are not pointless, but expect lower success and a longer wait.

Aftercare

Harden ailsa craig onion off over a week before planting out, water transplants in well, and protect them from late cold snaps. Steady moisture and the parent's light needs carry them through establishment. Match the parent's needs as the new ailsa craig onion settles: Requires full sun — minimum 6 hours daily. Long summer days trigger bulb initiation; siting in full light maximises bulb size and ripening.

Ailsa Craig Onion propagation — frequently asked questions

What is the best way to propagate ailsa craig onion?

Seed (with cuttings or suckering as a shortcut where possible) is the most reliable method for ailsa craig onion. Propagate ailsa craig onion mainly from seed — start it indoors 6–8 weeks before your last frost, or sow direct when soil warms. Where the plant suckers or roots from softwood, a cutting is a faster shortcut to a true-to-type clone of a favourite specimen.

Do you need a node to propagate ailsa craig onion?

For ailsa craig onion the rooting structure is seed (with cuttings or suckering as a shortcut where possible), so a classic "node" matters less than starting with the right plant material — Where the plant suckers or roots from softwood, a cutting is a faster shortcut to a true-to-type clone of a favourite specimen..

How long does it take ailsa craig onion to root?

Seed to transplant in 4–8 weeks. Timing varies with warmth and light — propagations move fastest in spring and summer when the plant is in active growth, and can stall almost completely in a cold, dark winter.

What is the best time of year to propagate ailsa craig onion?

Start indoors 6–8 weeks before last frost. Root and shoot development is metabolically demanding, so propagating during the active growing season gives noticeably higher success rates and faster results than attempting it in dormancy.

Can you propagate ailsa craig onion in water?

Where ailsa craig onion can be taken as a softwood cutting, that cutting can often be water-rooted; the main route, though, is seed sown into compost rather than water.