How to Grow Onion

Onion

Allium cepa

vegetable

Onions 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.

Looking for a specific variety?

Yellow Sweet Spanish Texas 1015 Walla Walla Red Burgundy White Bermuda Candy

Growing Conditions

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Sun: Full sun, 8+ hours daily for optimal bulb development

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Water: Consistent moisture; about 1-2 inches per week. Keep soil evenly moist but not waterlogged during bulb formation. Reduce watering after tops fall over to prevent rot.

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Spacing: 4-6 inches apart in rows 12-18 inches apart inches

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Days to maturity: 90-180 days depending on variety and growing method

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Planting depth: Plant sets 1 inch deep; transplants at same depth as in containers; seeds 0.25-0.5 inch deep

Soil

Type: Well-draining loamy soil rich in organic matter

pH: 6.0-6.8

Amendments:

Compost or aged manure (2-3 inches worked in) Nitrogen-rich fertilizer at planting Sulfur to lower pH if needed Bone meal for phosphorus

Growing Zones

Find your zone →

Thrives in zones 3-9; can be grown in zones 2 and 10 with variety selection

2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a 10b

Growth Stages

Seed or Set Germination

1-2 weeks

Seeds 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 weeks

Tall, 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 weeks

Bulbs 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 weeks

Bulbs 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 ready

Approximately 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.

Companion Planting

Plan your garden →

Plant with:

Beets Cabbage Carrot Chard Lettuce Parsnip Strawberry Tomato

Avoid planting near:

Asparagus Bean Pea Sage

Common Pests

Use row covers over young plants; practice crop rotation; apply beneficial nematodes to soil; harvest immediately if infestation detected
Spray with insecticidal soap or neem oil; reflective mulches deter them; encourage beneficial insects
Use disease-resistant varieties; ensure excellent drainage; disinfect tools; remove infected bulbs immediately; practice 3-year crop rotation
Improve air circulation; avoid overhead watering; remove infected leaves; apply sulfur or copper fungicide; choose resistant varieties
Plant resistant varieties; practice crop rotation; disinfect seeds and sets; improve drainage and avoid excessive moisture

Uses

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Cooking & flavor base

Culinary

Onions 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]

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Immune support & cardiovascular health

Medicinal

Onions contain quercetin and organosulfur compounds that have anti-inflammatory, antimicrobial, and antioxidant properties. Traditional medicine uses onion for cough, cold, and respiratory support. [source]

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Natural cleaning & skin care

Household

Onion 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]

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Pollinator nectar & beneficial insect support

Wildlife

Onion flowers (when allowed to bolt) produce nectar that attracts bees, hoverflies, and other beneficial insects critical for garden pollination. [source]

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Pickling & preservation

Culinary

Pickled 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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