How to Grow Potato Onion
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Potato Onion
Allium cepa var. aggregatum
vegetablePotato onions are a rare, heirloom multiplier onion that produces clusters of small to medium-sized bulbs underground, similar to how potatoes grow. They are sweeter and milder than traditional onions, with a unique nutty flavor when cooked. These cold-hardy perennials can be grown as annuals or left in the ground to multiply year after year.
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Example Potato Onion timeline · Pittsburgh, PA (Zone 6b)
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Plant Potato Onion
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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Harvest Potato Onion
Around Jul 16≈ 90 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Potato Onion dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Zones 3-9; excellent cold tolerance makes them ideal for northern gardeners
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Dormancy/Planting
Planting phase, bulblets begin rooting within 2-3 weeksSmall bulblets from previous year are dormant and ready for planting in fall or early spring.
Store bulblets in cool, dry conditions. Plant in fall (September-November) in mild climates or early spring in cold areas. Choose healthy, disease-free bulblets.
Emergence & Early Growth
3-4 weeks after emergenceGreen shoots emerge from soil and develop into thin, tube-like leaves similar to regular onions.
Ensure consistent moisture and remove any weeds. Mulch around plants to retain moisture and regulate soil temperature. Monitor for pests.
Vegetative Development
6-8 weeksFoliage grows taller (6-12 inches) and develops multiple leaves. Underground, the mother bulblet begins dividing into a cluster of new bulblets.
Continue regular watering and weeding. Side-dress with compost or balanced fertilizer if growth appears slow. This is the critical phase for bulb multiplication.
Maturation & Dormancy
2-3 weeksFoliage yellows and begins to dry down. Underground bulblet cluster reaches full size (typically 4-8 bulblets per cluster). Necks weaken as plant enters dormancy.
Reduce watering significantly once tops yellow. Do not water excessively or you risk rot. Allow foliage to fully dry before harvest to ensure proper curing.
Harvest & Storage
Harvest phase; storage duration is 6-12 monthsFoliage is completely dry and brown. Bulblet clusters are ready to lift and cure.
Harvest when foliage is fully dry. Cure in a warm, dry, well-ventilated area for 2-3 weeks. Store in cool (40-50°F), dry conditions with good air circulation.
Common Pests
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Use row covers over young plants, practice crop rotation, remove affected bulbs immediately, apply neem oil if infestation occurs
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Spray with water to dislodge, use insecticidal soap, introduce beneficial insects like predatory mites, avoid excessive nitrogen
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Ensure proper air circulation, avoid overhead watering, cure bulbs thoroughly before storage, store in cool, dry conditions, remove affected bulbs
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Practice 4-year crop rotation, plant disease-resistant varieties, improve soil drainage, avoid replanting in same location
Uses
Sweet, Mild Flavored Cooking Onion
CulinaryPotato onions have a distinctly sweeter, milder, and nuttier flavor than common onions, making them ideal for caramelizing, roasting, and creamed preparations. Their delicate taste shines in elegant side dishes and soups. [source]
Pickling & Preservation
CulinaryThe small to medium size and thin skins make potato onions excellent for pickling whole or in halves. They are popular in traditional European preserves and condiments. [source]
Seed Saving & Self-Sufficiency
HouseholdPotato onions are a true heirloom multiplier crop; plant once and harvest multiple bulblets each year without replanting. They are ideal for gardeners seeking food security and reducing annual seed/bulb purchases. [source]
Traditional Immune & Digestive Support
MedicinalLike all onions, potato onions contain quercetin, allicin, and sulfur compounds with traditional use in folk medicine for immune health, anti-inflammatory effects, and digestive support. [source]
Pollinator & Beneficial Insect Support
WildlifeIf allowed to bolt and flower (rare in short-season areas), potato onions produce delicate purple-pink flowers that attract bees, butterflies, and other beneficial insects. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Harvest when foliage has completely yellowed and dried down, typically 90-120 days after planting. Gently dig around clusters to avoid damaging bulblets. Cure in a warm (70-80°F), dry, well-ventilated area for 2-3 weeks before storage. Store in a cool basement or root cellar at 40-50°F with 65-70% humidity. Properly cured potato onions store 6-12 months. Reserve the largest bulblets for replanting next season.
Fun Facts
- 🌱 Potato onions earned their name because they multiply underground like potatoes, creating a cluster of bulblets from a single planted bulblet—one planting can yield 4-8 bulbs at harvest.
- 🌱 This is one of the oldest and most endangered heirloom onion varieties in North America, nearly lost to history until seed savers and heritage gardeners revived it in the 1990s.
- 🌱 Potato onions were a staple in European kitchen gardens for centuries and are still prized by European gardeners; they are sometimes called 'multiplier onions' or 'Egyptian onions' in different regions.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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