Repotting guide

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

Also called cipollini onion, flat Italian onion, borettane onion.

More about cipollini onion

About Cipollini Onion

Allium cepa 'Cipollini' · also called cipollini onion, flat Italian onion · edible

Cipollini is a small, flat Italian onion prized for its sweet, high-sugar flesh that caramelises beautifully when roasted whole. An intermediate-day cool-season biennial grown as an annual, it sizes up in full sun and rich, loose soil over about 100-110 days before the tops fall and bulbs cure for storage.

Mature size: Tops 30-40cm tall; bulbs flat discs about 5-7cm wide and 2-3cm thick.

How to tell cipollini onion needs repotting

Repotting on a calendar is less reliable than reading the plant. For cipollini 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 cipollini 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 cipollini onion

Lift and divide every 3–4 years once clumps congest. Rather than a true repot, cipollini onion is lifted and divided once the clump congests and flowering drops off. Clumping biennial bulb grown as an annual, forming a fan of hollow blue-green tubular leaves above a single squat, flattened bulb that sits at the soil surface..

What size pot to step cipollini onion up to

Pot size matters less than depth and spacing here. When you replant cipollini 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 cipollini 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 cipollini onion in full growth or flower sets it back badly.

Step-by-step: repotting cipollini onion

Wait for dormancy. Let cipollini 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 loose, fertile, well-drained loam, ph 6.0-6.8 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 cipollini 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 cipollini onion

Cipollini Onion wants loose, fertile, well-drained loam, ph 6.0-6.8. Works best in friable soil free of stones and clods so the flat bulbs can expand at the surface. Raised beds enriched with compost give the loose, fast-draining tilth these shallow-rooted bulbs prefer. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting cipollini onion — frequently asked questions

How often should you repot cipollini onion?

Lift and divide every 3–4 years once clumps congest for cipollini onion. Cipollini 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 loose, fertile, well-drained loam, ph 6.0-6.8. Crowding, not pot size, is what reduces flowering over time.

What size pot does cipollini onion need?

When is the best time of year to repot cipollini onion?

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

You lift and divide it. Cipollini 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 cipollini onion after repotting?

Hold off feeding cipollini 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.