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Vegetable · Amaryllidaceae family

Welsh onion

Allium fistulosum

Full sun to part shade 11¾ in–2 ft 11⅜ in × 11¾ in–1 ft 11⅝ in Harvest May–November to −68 °F

In short a 10-second read

SunFull sun to part shade
Size11¾ in–2 ft 11⅜ in
spacing 7¾ in
Water~2.06 qt/sq ft
a week in a dry summer
SowingMarch–August
HarvestMay–November
WinterNo winter protection

Where to plant and how much to water

Sun, soil and water.

It grows best in full sun to part shade, in average soil.

Sun

Sun6 hours or more
Part shade3–6 hours
Shadeunder 3 h

Soil

acidic to neutral soil
acidicneutralalkaline
averageloamyhumus-richsandy

Watering

Welsh onion — Watering
~2.06 qt/sq fta week in a dry summer
keep the soil evenly moistless when it rains

Frost

−68 °F
no winter protection

How much space it takes

Mature size.

The mature plant next to a person (69 in).

19¾ in3 ft 3⅜ in4 ft 11 in11¾ in–2 ft 11⅜ inspread 11¾ in–1 ft 11⅝ in
11¾ in–2 ft 11⅜ in× spread 11¾ in–1 ft 11⅝ in

Plant 7¾ in apart.

How to plant: in clumps, clumps 9¾ in apart

The final size depends on the cultivar and the spot — we give the range from smallest to largest.

Calendar

Through the year.

Typical for a temperate climate (four seasons). The line shows the current month.

The year at a glance

Sowing: JanuarySowing: FebruarySowing: MarchSowing: AprilSowing: MaySowing: JuneSowing: JulySowing: AugustSowing: SeptemberSowing: OctoberSowing: NovemberSowing: DecemberHarvest: JanuaryHarvest: FebruaryHarvest: MarchHarvest: AprilHarvest: MayHarvest: JuneHarvest: JulyHarvest: AugustHarvest: SeptemberHarvest: OctoberHarvest: NovemberHarvest: DecemberProtection: JanuaryProtection: FebruaryProtection: MarchProtection: AprilProtection: MayProtection: JuneProtection: JulyProtection: AugustProtection: SeptemberProtection: OctoberProtection: NovemberProtection: DecemberJanFebMarAprMayJunJulAugSepOctNovDec
SowingHarvestProtection
Now, in October: time to harvest. · Protection – Cover Welsh onions with fine mesh during the leaf miner's flight period (March–April, September–October). · watch for allium leaf miner.
JanFebMarAprMayJunJulAugSepOctNovDec

Sowing

JanFebMarAprMayJunJulAugSepOctNovDec

direct sowing: March–August

Harvest

JanFebMarAprMayJunJulAugSepOctNovDec

May–November

Protection

JanFebMarAprMayJunJulAugSepOctNovDec

March–April, September–October (protection): Cover Welsh onions with fine mesh during the leaf miner's flight period (March–April, September–October).

Feeding

Nutrition.

Moderate
nitrogen-rich fertilizer

Pests and diseases

Common problems and what to do.

The most common problems in Central Europe. Protection is listed from the gentlest option.

High riskMedium riskLow riskRisk for this plant according to the source · no label = no documented level
Allium leaf miner

Allium leaf miner

Phytomyza gymnostoma
High riskpestsource covers the whole genus
More about this problem

What you will see

White tunnels on leaves, with larvae or brown pupae in the stems and bulbs; rot follows.

The source says: it is a serious threat to allium crops.

When to look

JanFebMarAprMayJunJulAugSepOctNovDec
March–June, September–October

How to protect

  1. Prevention
    • Cover plants with fine mesh during the fly's flight period (peak March–April and September–October).
    • Rotate crops, otherwise flies can emerge from pupae under the mesh.
  2. By hand at the first symptomsRemove affected plants early and dispose of them.
Allium leaf minerpest · March–June, September–OctoberHigh risk

What you will see

White tunnels on leaves, with larvae or brown pupae in the stems and bulbs; rot follows.

The source says: it is a serious threat to allium crops.

When to look

JanFebMarAprMayJunJulAugSepOctNovDec
March–June, September–October

How to protect

  1. Prevention
    • Cover plants with fine mesh during the fly's flight period (peak March–April and September–October).
    • Rotate crops, otherwise flies can emerge from pupae under the mesh.
  2. By hand at the first symptomsRemove affected plants early and dispose of them.
More about this problem
Onion white rot

Onion white rot

Stromatinia cepivora
High riskdiseasesource covers the whole genus
More about this problem

What you will see

Yellowing and wilting leaves, rotting roots and onion base.

The source says: it is a serious disease of the onion family.

When to look

Midsummer to early fall

How to protect

  1. Prevention
    • You can practically never clean soil once it has white rot: prevent it being introduced (soil on tools and footwear).
    • Do not grow alliums on affected soil.
  2. By hand as soon as it appearsDig up affected plants together with the surrounding soil and dispose of them; no chemical soil treatment is available to gardeners.
Onion white rotdisease · midsummer to early fallHigh risk

What you will see

Yellowing and wilting leaves, rotting roots and onion base.

The source says: it is a serious disease of the onion family.

When to look

Midsummer to early fall

How to protect

  1. Prevention
    • You can practically never clean soil once it has white rot: prevent it being introduced (soil on tools and footwear).
    • Do not grow alliums on affected soil.
  2. By hand as soon as it appearsDig up affected plants together with the surrounding soil and dispose of them; no chemical soil treatment is available to gardeners.
More about this problem
Onion downy mildew

Onion downy mildew

Peronospora destructor
diseasesource covers the whole genus
More about this problem

What you will see

Leaves yellow and die back, with a mold layer that is first white, then purple.

When to look

Late spring and summer

How to protect

  1. Prevention
    • Avoid crowded and sheltered, windless spots; weed so air can circulate.
    • Do not plant soft, moldy bulbs.
    • Dispose of affected plants and do not plant onions or shallots there for 5 years.
  2. By hand as soon as it appearsRemove affected plants and dispose of them.
Onion downy mildewdisease · late spring and summer

What you will see

Leaves yellow and die back, with a mold layer that is first white, then purple.

When to look

Late spring and summer

How to protect

  1. Prevention
    • Avoid crowded and sheltered, windless spots; weed so air can circulate.
    • Do not plant soft, moldy bulbs.
    • Dispose of affected plants and do not plant onions or shallots there for 5 years.
  2. By hand as soon as it appearsRemove affected plants and dispose of them.
More about this problem
Leek rust

Leek rust

Puccinia porri
diseasesource covers the whole genus
More about this problem

What you will see

Bright orange pustules on the leaves.

When to look

Midsummer to late fall

How to protect

  1. Prevention
    • The disease is worse on soil rich in nitrogen and poor in potassium: feed carefully.
    • Try varieties that suppliers list as more resistant (this is only partial resistance).
  2. By hand as soon as it appearsRemove affected leaves and dispose of them; do not overfeed with nitrogen.
Leek rustdisease · midsummer to late fall

What you will see

Bright orange pustules on the leaves.

When to look

Midsummer to late fall

How to protect

  1. Prevention
    • The disease is worse on soil rich in nitrogen and poor in potassium: feed carefully.
    • Try varieties that suppliers list as more resistant (this is only partial resistance).
  2. By hand as soon as it appearsRemove affected leaves and dispose of them; do not overfeed with nitrogen.
More about this problem
Sources (6)

Bed neighbors

Good and bad neighbors.

Each neighbor shows how we know it.

✓Good neighbors

✕Bad neighbors

  • Pea expert advice

Frequently asked

Quick answers.

When do I sow Welsh onion?

In March–August (direct sowing).

When is Welsh onion harvested?

In May–November.

Does Welsh onion tolerate shade?

It tolerates part shade (3–6 hours of sun), but not full shade.

How much space does Welsh onion need?

At maturity 11¾ in–1 ft 11⅝ in wide and 11¾ in–2 ft 11⅜ in tall; recommended spacing 7¾ in.

Allium leaf miner — what can you do?

Cover plants with fine mesh during the fly's flight period (peak March–April and September–October). Remove affected plants early and dispose of them.

Onion white rot — what can you do?

You can practically never clean soil once it has white rot: prevent it being introduced (soil on tools and footwear). Dig up affected plants together with the surrounding soil and dispose of them; no chemical soil treatment is available to gardeners.

Sources (4) Checked 27 October 2026

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