Repotting guide

When & how to repot 'Walla Walla' Onion (Allium cepa 'Walla Walla')

Also called Walla Walla sweet onion.

More about 'walla walla' onion

About 'Walla Walla' Onion

Allium cepa 'Walla Walla' · also called Walla Walla sweet onion · edible

'Walla Walla' is a famous short-to-intermediate-day sweet onion with very large, mild, juicy bulbs low in pungency. Traditionally autumn-sown for overwintering and summer harvest, it stores poorly and is best eaten fresh. It needs full sun, rich moist soil, and steady feeding to size up its big, thin-skinned bulbs.

Mature size: Foliage 30-45 cm tall; bulbs very large, commonly 10-15 cm across and up to 0.5-1 kg.

How to tell 'walla walla' onion needs repotting

Repotting on a calendar is less reliable than reading the plant. For 'walla walla' onion, watch for these signs:

Flowering has tailed off year on year and the clump has become congested and overcrowded.
Lots of leaf and few flowers — a classic sign that 'walla walla' onion bulbs or tubers need lifting and dividing.
Bulbs visibly bursting the pot or pushing each other to the surface.
It is the natural dormancy window (foliage yellowed and died back) — the only safe time to lift and split.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot 'walla walla' onion

Lift and divide every 3–4 years once clumps congest. Rather than a true repot, 'walla walla' onion is lifted and divided once the clump congests and flowering drops off. 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..

What size pot to step 'walla walla' onion up to

Pot size matters less than depth and spacing here. When you replant 'walla walla' onion, set the bulbs or tubers at the correct depth (a rough guide: two to three times their own height of soil over the top) and space them so they are not touching. A wide, shallow pot suits a clump better than a tall narrow one.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot 'walla walla' onion

The only safe window is dormancy: wait until the foliage has yellowed and died back naturally, lift and divide then, and replant before or at the start of the next growing season. Disturbing 'walla walla' onion in full growth or flower sets it back badly.

Step-by-step: repotting 'walla walla' onion

Wait for dormancy. Let 'walla walla' onion foliage yellow and die back completely. Lifting while it is in growth wastes the energy it is storing for next year.
Lift carefully. Loosen the soil well away from the bulbs/tubers with a fork and ease the whole clump out without spearing them.
Separate the offsets. Gently pull the clump apart into individual bulbs or tubers. Keep only firm, healthy, blemish-free ones.
Replant at the right depth. Reset them in fresh fertile, well-drained loam high in organic matter, ph 6.0-7.0 at the correct depth and spacing — not touching — so each has room to bulk up.
Water in and rest. Water once to settle them, then keep on the dry side until growth resumes. Do not feed until leaves are actively growing.

Aftercare

After replanting 'walla walla' onion, keep the soil barely moist — not wet — until shoots appear; bulbs and tubers rot in cold, saturated soil. Once leaves are growing strongly, resume normal watering. Hold off feeding until the plant is in active growth again.

The right soil mix for 'walla walla' onion

'Walla Walla' Onion wants fertile, well-drained loam high in organic matter, ph 6.0-7.0. Wants rich, friable soil with steady moisture but no waterlogging. Loose ground lets the large bulbs expand freely; firm or stony soil restricts size. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting 'walla walla' onion — frequently asked questions

How often should you repot 'walla walla' onion?

Lift and divide every 3–4 years once clumps congest for 'walla walla' onion. 'Walla Walla' Onion is lifted and divided, not "repotted". Every 3–4 years, once the foliage has died back and it is dormant, lift the clump, separate the offsets, and replant at the correct depth in fertile, well-drained loam high in organic matter, ph 6.0-7.0. Crowding, not pot size, is what reduces flowering over time.

What size pot does 'walla walla' onion need?

When is the best time of year to repot 'walla walla' onion?

Do you "repot" 'walla walla' onion, or lift and divide it?

You lift and divide it. 'Walla Walla' Onion grows from bulbs or tubers, so instead of repotting you wait for dormancy, lift the congested clump, separate the healthy offsets, and replant them at the right depth and spacing. Doing this every 3–4 years restores flowering.

Should you fertilise 'walla walla' onion after repotting?

Hold off feeding 'walla walla' onion until it is in active growth again. Fresh soil already carries enough nutrients to get it re-established, and feeding disturbed roots too soon does more harm than good.