Propagation guide

How to propagate 'Walla Walla' Onion (Allium cepa 'Walla Walla') — step by step

Also called Walla Walla sweet onion.

The best way to propagate 'walla walla' onion

The reliable, beginner-friendly way to propagate 'walla walla' onion is seed (with cuttings or suckering as a shortcut where possible). It suits this species because of how it grows: biennial bulb grown as an annual; upright tubular blue-green leaves arising from a single flattened, very large bulb. if overwintered and stressed it may bolt and send up a flower scape.. From seed or sets. For the classic large bulbs, sow seed in late summer to overwinter, or sow indoors in late winter for spring transplanting; thin or space 10-15 cm apart. Sets are quicker but more prone to bolting in this variety.

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 'walla walla' onion

Start seed indoors. Sow 'walla walla' 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 'walla walla' 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 'walla walla' 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 'walla walla' 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 'walla walla' onion settles: Full sun, at least 6-8 hours daily, is essential for bulbing. As an intermediate-day onion it bulbs when daylength reaches about 13-14 hours, so site and timing matter.

'Walla Walla' Onion propagation — frequently asked questions

What is the best way to propagate 'walla walla' onion?

Seed (with cuttings or suckering as a shortcut where possible) is the most reliable method for 'walla walla' onion. Propagate 'walla walla' 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 'walla walla' onion?

For 'walla walla' 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 'walla walla' 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 'walla walla' 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 'walla walla' onion in water?

Where 'walla walla' 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.