Onions (Allium cepa) are versatile and essential vegetables used worldwide for their unique flavor and numerous health benefits. They are biennial plants but are typically grown as annuals for their bulbs. Growing onions from seed can be a rewarding process, allowing you to choose from a wide variety of types not always available as sets or transplants. With the right conditions and care, you can enjoy a bountiful harvest of homegrown onions.
Ideal Weather Conditions for Growing Onions
Condition
Ideal Range
Temperature
55°F to 75°F (13°C to 24°C)
Soil pH
6.0 to 6.8
Sunlight
Full sun (6-8 hours daily)
Watering
Moderate, well-drained soil
Choosing the Right Seed
From the Shop
Variety Selection: Choose seeds based on the onion variety you prefer (e.g., sweet onions, red onions, storage onions).
Freshness: Check the packaging date and ensure seeds are not older than two years.
Certification: Opt for seeds that are certified organic or untreated to avoid chemical residues.
Collecting and Preserving Seeds
Seed Collection: Allow some onion plants to flower and form seed heads. Once the heads dry, collect the seeds.
Cleaning: Separate the seeds from the chaff and store them in a cool, dry place.
Storage: Keep seeds in airtight containers in a refrigerator to maintain viability.
Growing Seedlings from Seed
Seed Starting Time: Start seeds indoors 8-10 weeks before the last expected frost date.
Seedling Trays: Fill trays with a seed-starting mix.
Sowing Seeds: Sow seeds 1/4 inch deep and 1 inch apart.
Watering: Keep the soil consistently moist but not waterlogged.
Lighting: Place trays under grow lights or in a sunny window for 12-16 hours a day.
Thinning: Once seedlings are 2 inches tall, thin them to 2-3 inches apart.
Nutrition Requirements for Onions
Nutrient
Importance
Nitrogen (N)
Promotes leaf growth and overall vigor
Phosphorus (P)
Essential for root development
Potassium (K)
Improves disease resistance and bulb quality
Calcium (Ca)
Strengthens cell walls and prevents rot
Magnesium (Mg)
Vital for photosynthesis
Sulfur (S)
Enhances flavor and pungency
Organic Soil Mix for Onions
Ingredient
Amount
Ratio
Compost
2 parts
40%
Garden soil
2 parts
40%
Sand
1 part
20%
Bone meal
1 cup per 5 gallons of mix
N/A
Organic fertilizer (5-10-10)
1 cup per 5 gallons of mix
N/A
Preparing the Soil Mix
Mix Ingredients: Combine compost, garden soil, and sand in the indicated ratios.
Add Nutrients: Mix in bone meal and organic fertilizer thoroughly.
Preparation: Ensure the soil is well-draining and rich in organic matter before planting.
Transferring Seedlings to Garden or Raised Bed
Hardening Off: Gradually expose seedlings to outdoor conditions over 7-10 days.
Bed Preparation: Amend garden soil with compost and organic fertilizer.
Watering: Water thoroughly after planting and keep soil moist but not waterlogged.
Care Throughout Different Growth Stages
Initial Growth (Weeks 1-4)
Watering: Keep soil consistently moist.
Fertilizing: Apply a balanced, organic fertilizer at half strength.
Weeding: Keep beds weed-free to reduce competition.
Bulb Development (Weeks 5-10)
Watering: Water deeply once a week.
Fertilizing: Side-dress with compost or a high-phosphorus fertilizer.
Pruning: Remove any flower stalks to encourage bulb growth.
Maturity (Weeks 11-16)
Watering: Reduce watering as bulbs mature to prevent rot.
Fertilizing: Stop fertilizing 2-3 weeks before harvest.
Monitoring: Check for pests and diseases regularly.
Harvesting and Preserving Onions
Timing: Harvest onions when tops turn yellow and fall over.
Lifting: Carefully lift bulbs with a fork to avoid damage.
Curing: Cure onions by laying them out in a dry, shaded area with good air circulation for 2-3 weeks.
Storing: Store cured onions in a cool, dry place. Mesh bags or open crates work well for maintaining air circulation.
Preservation: Onions can also be frozen, dried, or pickled for longer storage.
By following these detailed steps, you can successfully grow onions from seed and enjoy a bountiful harvest. Each stage of growth requires careful attention, but the reward of homegrown onions is well worth the effort.
