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Onion

Allium cepa

The aromatic layered bulb that brings depth and character to every dish—patient, reliable, and surprisingly rewarding to grow.

🌱 Root Zone: Shallow
🌱 Annual ☀️ Full Sun 💧 Moderate Water 🌡️ Zones 3-9
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Best Roommates 12

Carrot

Onion repels carrot rust fly with sulfurous aroma; both thrive in cool season

Radish

Fast-growing radish marks slow-developing onion rows; harvests before onion needs space

Tomato

Onion's sulfur compounds repel aphids, whiteflies, and spider mites that attack tomatoes

Marjoram

Similar benefits to oregano; combined aromatic oils enhance pest deterrence

Basil

Both favor similar conditions; complementary pest-repelling properties strengthen garden health

Chives

Same family; compatible growing requirements; complementary pest control

Nasturtium

Trap crop for aphids and other pests; provides living ground cover

Cucumber

Onion's pungent aroma repels pests affecting cucumber while using different root depths

Marigold

Both attract beneficial insects; marigold suppresses nematodes while onion repels flies

Dill

Dill attracts beneficial parasitic insects; no competition between plants

Oregano

Oregano attracts beneficial insects; both repel flying pests

Parsley

Parsley attracts beneficial predatory insects; no nutrient competition

Keep Your Distance 3

Fennel

Fennel's allelopathic compounds inhibit onion growth and development

Kohlrabi

Heavy feeder that competes for nutrients with developing onion bulbs

Bean

Beans can stunt onion growth through allelopathic effects

Growing Guide

🌱 Planting

  • Start seeds indoors 6-8 weeks before last frost
  • Transplant when soil reaches 65°F (18°C)
  • Space plants 18-24 inches apart
  • Plant in well-draining, rich soil with pH 6.0-6.8

💧 Water & Soil

  • Water deeply 1-2 inches per week
  • Mulch to retain moisture and prevent weeds
  • Consistent watering prevents fruit cracking
  • Avoid wetting foliage to prevent disease

☀️ Light & Temperature

  • Requires 6-8 hours of direct sunlight daily
  • Ideal temperatures: 70-85°F (21-29°C)
  • Protect from strong winds
  • Use row covers in cooler climates

🌿 Care & Maintenance

  • Stake or cage plants for support
  • Prune suckers below the first flower cluster
  • Fertilize every 2-3 weeks during fruiting
  • Monitor for common pests and diseases

Harvesting & Storage

🍅 When to Harvest

  • Harvest when fully colored but still firm
  • Ripe when gently pressed gives slightly
  • Best flavor developed at room temperature
  • Check daily during peak season

🏠 Storage Tips

  • Store at room temperature out of direct sun
  • Avoid refrigeration (cold ruins flavor/texture)
  • Use within 5-7 days for best quality
  • Can be frozen, canned, or dried for preservation

Troubleshooting Guide

🐛 Common Pests

  • Hornworms: Hand-pick or use Bt
  • Aphids: Spray with soapy water
  • Whiteflies: Use yellow sticky traps
  • Spider Mites: Increase humidity, use neem oil

🦠 Common Diseases

  • Early Blight: Remove affected leaves, improve airflow
  • Blossom End Rot: Ensure consistent calcium supply
  • Cracking: Maintain even watering
  • Powdery Mildew: Increase air circulation

Get Growing

Ready to add Onion to your garden? Find high-quality organic seeds to get started.

Find Onion Seeds

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Common Questions

What are the best companion plants for Onion?

Onion (Allium cepa) is a shallow root plant. The best companions include Carrot, Radish, Tomato, Marjoram, Basil, Chives, Nasturtium, Cucumber, Marigold, Dill, Oregano, Parsley.

What should you NOT plant next to Onion?

Avoid planting Fennel, Kohlrabi, Bean near Onion as they may compete for nutrients or attract similar pests.

Can I grow Onion in a container?

Yes! Onion has a shallow root system, making it ideal for container gardening.

Onion (Allium cepa): The Ultimate Growing & Care Guide

Quick Growing Stats

  • Days to Harvest: 90-120 days
  • Plant Height: 12-18 inches
  • Spacing: 4-6 inches between plants
  • Row Spacing: 12-15 inches
  • Sunlight: Full sun (6-8 hours daily)
  • Water Needs: Consistent moisture, 1 inch per week
  • Soil pH: 6.0-6.8

Why Grow Onions? Your Garden's Flavor Powerhouse

Onions are more than just a kitchen staple—they're a versatile, nutritious crop that can transform your garden's productivity. Packed with antioxidants, vitamin C, and anti-inflammatory compounds, these allium vegetables offer tremendous health benefits while adding depth to countless recipes.

Strategic Planting: Timing is Everything

Planting Strategies for Maximum Success

  • Spring Planting (Most Regions)
  • Start seeds indoors 8-10 weeks before last spring frost
  • Optimal soil temperature range: 50-75°F
  • Transplant when soil becomes workable
  • Typical planting window: Late February to early April
  • Fall Planting (Warmer Regions)
  • Plant 4-6 weeks before first fall frost
  • Ideal for USDA zones 7-9
  • Produces larger, more robust bulbs
  • Extended growing season advantage

Pro Planting Tip: Select varieties matched to your specific day length and climate zone for guaranteed success.

Planting Methods: Seeds vs. Sets vs. Transplants

  • Seeds
  • Most economical option
  • Greatest variety selection
  • Requires more time and attention
  • Best for patient, detail-oriented gardeners
  • Sets (Small Dormant Bulbs)
  • Fastest to mature
  • Beginner-friendly
  • Less susceptible to disease
  • Immediate garden integration
  • Transplants
  • Quick establishment
  • Minimal initial investment
  • Ideal for shorter growing seasons

Seed Starting Mastery

  • Use sterile, nutrient-rich seed starting mix
  • Plant seeds 1/4 inch deep
  • Maintain consistent soil moisture
  • Provide strong grow lights
  • Thin to strongest seedlings

Soil Preparation: The Foundation of Onion Success

Key Soil Requirements

  • Well-draining, rich loamy composition
  • High organic matter content
  • pH between 6.0-6.8
  • Full sun exposure (minimum 6 hours daily)

Soil Amendment Strategies

  • Incorporate compost or aged manure before planting
  • Avoid heavy clay soils
  • Consider raised beds for superior drainage

Companion Planting: Strategic Garden Allies

Beneficial Companions & Why They Work

  • Carrots: Repel onion flies, share nutrients
  • Beets: Maximize ground space, complementary root structures
  • Lettuce: Provides ground cover, reduces soil moisture evaporation
  • Strawberries: Enhance pest resistance, improve overall garden biodiversity

Incompatible Plants to Avoid

  • Beans and peas (compete for nutrients)
  • Other allium family members (disease cross-contamination risk)

Watering & Nutrition: Precision is Key

Watering Guidelines

  • Consistent moisture critical
  • 1 inch of water per week
  • Reduce watering as bulbs mature
  • Avoid waterlogging

Fertilization Strategy

  • High-nitrogen fertilizer during early growth
  • Transition to balanced formula mid-season
  • Avoid excessive nitrogen during bulb formation
  • Monthly compost side-dressing recommended

Pest & Disease Management

Top Pest Challenges

  • Thrips
  • Organic Solutions:
  • Neem oil treatment
  • Introduce beneficial insects
  • Regular crop rotation
  • Use reflective mulch
  • Onion Maggots
  • Prevention Tactics:
  • Implement row covers
  • Plant resistant varieties
  • Maintain garden hygiene
  • Use diatomaceous earth barriers
  • Cutworms
  • Control Methods:
  • Create plant collars
  • Handpick visible larvae
  • Apply beneficial nematodes
  • Use organic pest deterrents

Disease Prevention

  • Select disease-resistant varieties
  • Ensure proper air circulation
  • Avoid overhead watering
  • Practice strict crop rotation
  • Monitor plants regularly

Harvesting & Storage Mastery

Maturity Indicators

  • Tops yellowing and falling over
  • Bulbs slightly emerging from soil
  • Typically 90-120 days post-planting

Harvest Process

  • Cease watering when 50-75% of tops have fallen
  • Gently lift bulbs using garden fork
  • Cure in shaded, dry area for 7-10 days
  • Trim roots and tops
  • Sort by size and quality

Advanced Storage Techniques

  • Store in cool (32-40°F), dark environment
  • Maintain 65-70% humidity
  • Use mesh bags or ventilated containers
  • Properly cured onions last 3-6 months
  • Inspect monthly for spoilage

Regional Growing Adaptations

Northern Regions

  • Indoor seed starting crucial
  • Short-day variety selection
  • Frost protection strategies

Southern Regions

  • Fall/winter planting recommended
  • Heat-tolerant variety selection
  • Afternoon shade protection

Final Pro Tips

  • Experiment with multiple planting methods
  • Keep detailed garden journal
  • Save seeds from best-performing plants
  • Continuously learn and adapt

Happy Growing, Onion Enthusiasts! 🧅🌱

⚠️ Note: Some plant information on this site is AI-generated. While we strive for accuracy, we recommend verifying critical growing information with local extension services or horticultural experts before planting.