How to Grow Potato Onions UK

When to Plant Potato Onions in the UK

When to plant potato onions in the UK: in Southern England, sow early October to mid October. Find your area in the table below.

Quick Facts

At a Glance

Soil & Growing Conditions

Water: well-drained, organically rich (Cultivariable)

Growth Stages

Harvest & Storage

When to pick: Gently dig or pull once the tops start to die back and fall over (UMD Extension); usually July-August but can be harvested anytime after bulbing with quality holding through winter (Cultivariable). Store at 50-60°F (10-16°C) and low humidity -- often keeps more than a year in an open box in a cool pantry, notably better storage than shallots.

Diseases

Pests

Potato Onion, Cluster to Harvest

Larger and fewer than shallots

Cultivariable: "potato onions are larger, divide into fewer bulbs, and remain enclosed within the skin of the seed bulb longer" than shallots -- the key difference between two types that share the same Aggregatum Group.

One bulb becomes a hill

A single planted potato onion divides underground into a cluster or "hill" of typically six to eleven daughter bulbs (Cultivariable) -- far more yield per planting than a standard single-bulb onion.

A traditional Appalachian winter onion

Also called the hill onion or mother onion, potato onion has a long history as an overwintered "winter onion" in Appalachia, prized for storing far better than shallots.

Similar care to bulbing onions

UMD Extension groups potato onion with other perennial multiplier onions: care is broadly similar to standard bulbing onions, with mulch recommended over fall-planted bulbs against weeds and extreme cold.

A long-day bulbing plant

Cultivariable: most potato onion varieties are long-day plants, needing long summer days north of 37N latitude (or south of 37S) to bulb well.

References

1. Cultivariable - Potato Onion (Allium cepa var. aggregatum)

   A commercial grower reference rather than a university or horticultural authority, used for cultivation specifics (photoperiod, storage duration, differences from shallots) not covered by the University of Maryland Extension source, not contradicted by it. Fall or spring planting both work; fall planting gives earlier maturity (up to a month sooner) but may trigger flowering in some climates. In mild climates plant the bulb with the tip just at the surface; in colder climates plant deeper for protection. Prefers mildly acidic to neutral pH, organically rich, well-drained soil. Hardy to USDA zone 4 and potentially colder with snow cover or mulch. Most varieties are long-day plants requiring long days north of 37N latitude (or south of 37S) to bulb well. Can grow in containers, one plant per gallon pot, nearly equal yields to ground planting. Usually harvested July-August; can harvest anytime after bulbing, quality holds through winter. New leaves can be snipped as green onions year-round if limited to 10% of the plant. Store at 50-60°F (10-16°C), low humidity; will often store more than a year in an open box in a cool pantry. KEY DIFFERENCE FROM SHALLOTS: potato onions are larger, divide into fewer bulbs, and remain enclosed within the skin of the seed bulb longer; sharper flavour and superior storage compared to shallots' milder taste and poor storage. Relatively pest-free; onion fly mainly threatens seedlings. Vulnerable to viral diseases causing reduced yield and smaller bulb size over generations; starting from seed can produce virus-free plants.

2. University of Maryland Extension - Growing Onions in a Home Garden

2 independent sources are cited for this crop. Where they disagree - soil pH is the clearest case - every figure is preserved rather than averaged into false precision.