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Onion
Allium cepa
vegetableOnions are bulbous vegetables that form underground storage structures, producing tall, hollow leaves above ground. They are cool-season crops that tolerate frost and are grown worldwide for their pungent, flavorful bulbs used in countless cuisines. Available in sweet, pungent, and intermediate varieties, onions offer long storage life and year-round availability.
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Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 3-9; can be grown in zones 2 and 10 with variety selection
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Growth Stages
Seed or Set Germination
1-2 weeksSeeds germinate in 7-10 days; sets send up initial shoots. Roots establish in soil.
Keep soil consistently moist but not waterlogged. Ensure good drainage to prevent rot. Plant in cool season (spring or fall depending on day-length type).
Leaf Development
4-8 weeksTall, hollow green leaves emerge and elongate. Plant focuses on foliage production. Minimal bulb swelling occurs.
Water consistently and apply nitrogen fertilizer every 3-4 weeks. Thin seedlings to proper spacing. Remove any flower stalks that appear.
Bulb Initiation & Expansion
6-10 weeksBulbs begin to swell underground as day length and/or temperature trigger bulbing. Foliage continues growing but at slower rate.
Reduce nitrogen; apply phosphorus and potassium-rich fertilizer. Maintain even moisture—critical for proper bulb development. Apply mulch to retain moisture and regulate soil temperature.
Bulb Maturation
3-4 weeksBulbs enlarge significantly. Papery outer skin develops. Tops begin to yellow and fall over as bulbs near maturity.
Reduce watering as tops decline. Do not overwater—increases disease risk and splits bulbs. Stop fertilizing. Avoid disturbing bulbs.
Harvest-Ready & Dormancy
Harvest when readyApproximately 50% of tops have fallen over and died back. Bulbs are firm with dry, papery outer skin. Plant enters dormancy.
Stop watering 2 weeks before harvest to cure bulbs in ground. Harvest when tops are fully dried. Cure harvested bulbs in cool, well-ventilated location for 2-4 weeks before storage.
Common Pests
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Use row covers over young plants; practice crop rotation; apply beneficial nematodes to soil; harvest immediately if infestation detected
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Spray with insecticidal soap or neem oil; reflective mulches deter them; encourage beneficial insects
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Use disease-resistant varieties; ensure excellent drainage; disinfect tools; remove infected bulbs immediately; practice 3-year crop rotation
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Improve air circulation; avoid overhead watering; remove infected leaves; apply sulfur or copper fungicide; choose resistant varieties
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Plant resistant varieties; practice crop rotation; disinfect seeds and sets; improve drainage and avoid excessive moisture
Uses
Cooking & flavor base
CulinaryOnions are fundamental in cuisines worldwide, used as a savory base for soups, stews, curries, and sauces, or caramelized for complex sweetness. Raw onions add sharp flavor to salads, salsas, and garnishes. [source]
Immune support & cardiovascular health
MedicinalOnions contain quercetin and organosulfur compounds that have anti-inflammatory, antimicrobial, and antioxidant properties. Traditional medicine uses onion for cough, cold, and respiratory support. [source]
Natural cleaning & skin care
HouseholdOnion juice has been used in folk remedies for warts, burns, and skin irritation. Onion skins produce natural dyes for fabrics in warm yellow and brown tones. [source]
Pollinator nectar & beneficial insect support
WildlifeOnion flowers (when allowed to bolt) produce nectar that attracts bees, hoverflies, and other beneficial insects critical for garden pollination. [source]
Pickling & preservation
CulinaryPickled onions and pearl onions are popular condiments and cocktail garnishes. They preserve well and add tangy flavor to charcuterie boards and sandwiches. [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 50-75% of tops have fallen over and dried (typically late June-August in spring plantings). Gently loosen soil and pull bulbs. Brush off soil; do not wash. Cure in a warm, dry, well-ventilated location for 2-4 weeks until outer skin is completely papery and neck is dry. Store in cool (50-55°F), dry location with good air circulation; they keep 3-8 months depending on variety.
Fun Facts
- 🌱 Onions don't have layers—they are made of modified leaves wrapped concentrically around a central core, and each 'layer' is actually a complete leaf.
- 🌱 The pungent compounds in onions (sulfoxides) are released only when cells are broken; this is why cutting an onion makes you cry—enzymes create a gas that irritates your eyes.
- 🌱 Day-length varieties are critical: long-day types (for northern climates) require 14-16 hours of daylight to bulb, while short-day types (for southern regions) bulb at 10-12 hours, allowing year-round cultivation across different regions.
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