Welsh onion (Allium fistulosum) is a root or bulb crop well suited to the balcony: it grows in a pot of at least 6 L and needs 4–8 hours of direct sun a day. Below, the verified data and the practical notes for container growing.
Cycle and habit
annual or biennial grown as a seasonal crop; edible underground growth; depth and drainage are critical
In a pot it develops to roughly 20 cm tall and 10 cm wide. The exact final size depends on cultivar, climate and container — these figures are a reference, not a guarantee.
Light
The Welsh onion needs 4–8 hours of direct sun; acclimatise gradually.
If your balcony does not reach the minimum hours, choose the sunniest micro-climate: a south-facing, unshaded spot. For the full picture on sun by plant family, read Light on the balcony: how many sun hours per family.
Temperature and season
Prefers cool periods; protect from hard frost and shade during heatwaves.
It tolerates down to about 4 °C; below that, move it in or protect it from the coldest nights.
Substrate and drainage
Use a structural peat-free mix with mature compost and 20–30% drainage material; keep holes clear.
On a balcony the container is small and drains fast: keep the holes clear and empty the saucer after each watering. For what to put in the pot, read Substrate and drainage: what to put in the pot
Watering
Water when the top 2–3 cm dry; soak thoroughly and empty the saucer.
Pot soil dries much faster than ground soil: check it every day, especially in the hot season, rather than on a fixed calendar. For the complete watering method, read Watering in containers: how much and when
Technical sheet
- Botanical name
- Allium fistulosum
- Category
- Root or bulb crop
- Sun
- 4–8 h
- Min. pot
- 6 L
- Min. depth
- 18 cm
- Spacing
- 10 cm
- Difficulty
- Easy
- One pot
- No
Nutrition
Avoid excess nitrogen; a light feed is enough if growth slows.
In a pot the available nutrients run out sooner than in open ground, so a light, regular feed is what matters — not large, infrequent doses.
Sowing and transplanting
Sow or transplant in the stated season; avoid root stress, keep the crown at the same level and harden off for 5–7 days.
When moving to the final container, go straight into a pot of at least 6 L and 18 cm deep, so you do not need to repot again soon.
Spacing
Keep about 10 cm between plants: the right distance improves airflow and slows the spread of diseases.
Harvest
Harvest or deadhead with clean tools when the useful part is well formed; do not remove more than one third of the canopy at once.
Harvest in stages, taking only what is fully developed, so the plant keeps producing for longer.
Common problems
- water stress
- wind or reflected heat
- aphids/mites or diseases encouraged by poor airflow
Prevention is the strongest lever: correct watering, good airflow and checking the plant from the start cut most problems before they start.
Pot and space
Minimum volume 6 L, at least 18 cm deep
A pot that is too small limits the root system and makes the Welsh onion far more sensitive to heat and drought. If in doubt, go up a size.
