Repotting guide
When & how to repot Welsh Onion (Allium fistulosum)
Also called Bunching onion, Scallion, Spring onion, Japanese bunching onion.
More about welsh onion
About Welsh Onion
Allium fistulosum · also called Bunching onion, Scallion · edible
Welsh onion (Allium fistulosum) is a hardy perennial bunching allium grown for its hollow blue-green leaves and mild scallion-like stems. Unlike bulb onions it forms clumps rather than swelling bulbs, regrowing year after year. Sow in full sun, harvest leaves continuously, and divide established clumps every few seasons. It overwinters reliably and is extremely cold-tolerant.
Mature size: 30-50 cm tall, clumps spreading 15-30 cm wide
How to tell welsh onion needs repotting
Repotting on a calendar is less reliable than reading the plant. For welsh onion, watch for these signs:
- Roots circling the bottom of the module or pot, or poking out of the drainage holes.
- The seedling dries out within a day and growth has visibly stalled.
- Roots are white and matted in a tight spiral when you tip the plant out.
- It has outgrown its current container for the stage of the season — pot welsh onion on before it becomes hard root-bound.
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 welsh onion
Pot on seedlings as they grow; not a perennial repot. Welsh Onionis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Clump-forming perennial allium with upright hollow tubular leaves rising from a non-bulbing base; multiplies by basal offsets to form dense clumps..
What size pot to step welsh onion up to
Pot welsh onion on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check.
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 welsh onion
Pot welsh onion on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.
Step-by-step: repotting welsh onion
- Pot on before it is root-bound. Check welsh onion regularly; move it up as soon as roots reach the edge of the cell or pot, not after they have circled.
- Step up one or two sizes. Choose the next container up — not a giant one. Cold, wet, unused soil around a small root system stalls seedlings.
- Knock it out gently. Support the stem, tip the pot, and ease the rootball out without breaking it. A little teasing of circled roots at the base is fine.
- Pot into rich mix. Set it into fresh fertile, free-draining loam, ph 6.0-7.0 at the same depth (tomatoes are the exception — they can go deeper to root along the stem).
- Water in and grow on. Water well, keep it in good light, and resume feeding once it is established and growing again.
Aftercare
Water welsh onion in well and keep it in bright light; a freshly potted-on seedling can wilt for a day while roots settle, so do not overcompensate by drowning it. Do not fertilise for about 1 week — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.
The right soil mix for welsh onion
Welsh Onion wants fertile, free-draining loam, ph 6.0-7.0. Loose, well-worked soil enriched with compost. Good drainage is essential to prevent crown and root rot; raised beds suit heavier clay sites. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.
Repotting welsh onion — frequently asked questions
How often should you repot welsh onion?
Pot on seedlings as they grow; not a perennial repot for welsh onion. Welsh Onion is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into fertile, free-draining loam, ph 6.0-7.0 so the roots never circle the cell, ending in a large final container. A root-bound transplant stalls and never fully recovers.
What size pot does welsh onion need?
Pot welsh onion on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check. Use our pot size calculator to size it from the plant's current pot and root spread.
When is the best time of year to repot welsh onion?
Pot welsh onion on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.
Can you put welsh onion straight into a much bigger pot?
No. Even a fast-growing welsh onion should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.
Should you fertilise welsh onion after repotting?
Not immediately. Wait about 1 week after repotting welsh onion. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.
Related guides
- Welsh Onion care — light, water, soil and common problems
- How often to water welsh onion — the watering brief
- How to repot a plant — the complete step-by-step method
- Root-bound plant — how to spot and fix it
- Pot size calculator — size the next pot correctly
- When & how to repot tomato
- When & how to repot pepper
- When & how to repot cucumber
- All 1284 repotting guides in the Growli library