Welsh onion (scallion) Allium fistulosum
Welsh onion (scallion) (Allium fistulosum) is a deciduous perennial vegetable in the Amaryllidaceae family, native to Likely northwest China (cultivated across East Asia). It grows 40–70 cm (16–28 in) tall and 15–30 cm (6–12 in) wide, wants full sun and moderate water, and is hardy to about -30 °C (-22 °F). Space plants about 10 cm (4 in) apart.
Plan Welsh onion (scallion) in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
Welsh onion (scallion) at a glance
| Type | Perennial vegetable, deciduous |
|---|---|
| Family | Amaryllidaceae |
| Mature height | 40–70 cm (16–28 in) |
| Mature spread | 15–30 cm (6–12 in) |
| Spacing | 10 cm (4 in) centre to centre |
| Sun | Full sun, at least 5 h of direct sun a day |
| Water | Moderate; drought tolerance low, waterlogging tolerance low |
| Soil pH | 6–7.5 |
| Cold hardiness | About -30 °C (-22 °F) once established (roughly USDA zone 4) |
| Heat stress | Likely above about 30 °C (86 °F) |
| Flowering | from about May for 4–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Low |
| Pollinator value | Moderate |
| Edible | Yes: leaves, pseudostems, flowers |
| Native to | Likely northwest China (cultivated across East Asia) |
| Common in gardens of | 🇯🇵 Japan, 🇨🇳 China, 🇺🇸 United States, 🇰🇷 South Korea |
Is Welsh onion (scallion) toxic?
- People: not known to be toxic
- Cats: moderately toxic
- Dogs: moderately toxic
- Parts: leaves, bulbs
Alliums can damage red blood cells in cats and dogs.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Welsh onion (scallion)
No well-documented helpful pairing. Group it with plants that like full sun and moderate water.
Keep apart or take care
- caution With Legumes (pea family): Onions, garlic and leeks are said to stunt beans and peas (allium root exudates may reduce nodulation). Traditional companion-planting advice; controlled trials are few, so treat it as a soft preference. Evidence D
- caution With Legumes (pea family): Beans and peas are traditionally kept away from onions, garlic and leeks. Traditional companion-planting advice; controlled trials are few, so treat it as a soft preference. Evidence D
Shared pests and diseases
- White rot: Allium white rot survives in soil for 15+ years; never move infected soil. Evidence B
Questions about Welsh onion (scallion)
- How far apart should I plant Welsh onion (scallion)?
- About 10 cm (4 in) apart, centre to centre. A mature plant spreads 15–30 cm (6–12 in).
- Does Welsh onion (scallion) need full sun?
- Full sun: at least 5 hours of direct sun a day.
- How much water does Welsh onion (scallion) need?
- Moderate water. Drought tolerance is low and waterlogging tolerance low.
- How cold-hardy is Welsh onion (scallion)?
- It tolerates about -30 °C (-22 °F) once established, roughly USDA zone 4.
- When does Welsh onion (scallion) flower?
- From about May for 4–6 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Welsh onion (scallion) poisonous to cats and dogs?
- For cats it is moderately toxic; for dogs moderately toxic; for people not known to be toxic. Alliums can damage red blood cells in cats and dogs.
- What grows well with Welsh onion (scallion)?
- There is no well-documented companion pairing for Welsh onion (scallion). Group it with plants that like the same sun (full sun) and water (moderate).
Sources and evidence
Evidence grade C (C: plausible, mixed evidence).
- FAO Irrigation and Drainage Paper 56 — Crop Evapotranspiration, FAO
- RHS Plant Finder, Royal Horticultural Society
- University extension gardening guides (general), Various land-grant university extensions
Notes and assumptions
- Clumping perennial; often sown and pulled as an annual scallion crop. Kc taken from the FAO-56 green onion values.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Onion Allium cepa
- Daffodil Narcissus pseudonarcissus
- Garlic Allium sativum
- Leek Allium ampeloprasum (Porrum group)
- Chives Allium schoenoprasum
- Agapanthus Agapanthus praecox
- Ornamental allium Allium giganteum
- Shallot Allium cepa var. aggregatum