The Complete Guide to Growing Onions
From Planting to Harvest: Everything You Need to Know
Introduction to Onion Growing
Onions are a versatile and rewarding crop for home gardeners. With proper planning and care, you can grow flavorful onions that store well and provide the foundation for countless dishes. This guide will walk you through the entire process, from selecting the right varieties to harvesting and storing your crop.
Did You Know? Onions have been cultivated for over 5,000 years and were worshipped by ancient Egyptians who believed their concentric rings symbolized eternal life.
Popular Onion Varieties
Onions come in various types, each with distinct flavors, colors, and growing requirements. Consider your climate and culinary preferences when choosing varieties.
Onion Types by Day Length
Onions are categorized by how they respond to daylight hours, which determines when they form bulbs:
- Long-day varieties: Form bulbs when daylight reaches 14-16 hours (best for northern regions)
- Short-day varieties: Form bulbs when daylight reaches 10-12 hours (best for southern regions)
- Intermediate-day varieties: Form bulbs when daylight reaches 12-14 hours (versatile for middle regions)
Yellow Onions
All-purpose cooking onions with strong flavor that mellows when cooked.
Popular varieties: Yellow Globe, Copra, Patterson
Red Onions
Milder and slightly sweet, excellent for raw uses in salads and sandwiches.
Popular varieties: Red Wing, Red Zeppelin, Redwing
White Onions
Crisp and mild flavor, commonly used in Mexican cuisine and salads.
Popular varieties: Snowball, White Sweet Spanish
Sweet Onions
Mild and sweet with high water content, great for eating raw or lightly cooked.
Popular varieties: Vidalia, Walla Walla, Maui
Shallots
Delicate, sweet flavor with hints of garlic, excellent for gourmet cooking.
Popular varieties: French Grey, Zebrune
Bunching/Green Onions
Harvested young for their green tops and small white portions.
Popular varieties: Evergreen Hardy White, Tokyo Long White
Growing Methods: Seeds vs. Sets vs. Transplants
There are three primary ways to start growing onions. Each method has advantages and challenges:
| Method | Description | Advantages | Disadvantages |
|---|---|---|---|
| Seeds | Starting onions directly from seed |
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| Sets | Small, dormant bulbs from previous season |
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| Transplants | Young onion seedlings, usually 8-10 weeks old |
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Expert Tip: For beginners, start with sets for an easier experience. As you gain confidence, try transplants or seeds for larger bulbs and more variety options.
Ideal Growing Conditions
Soil Requirements
- Soil type: Loose, well-drained, fertile soil with sandy-loam to silt-loam texture
- pH level: 6.0 to 6.8 (slightly acidic)
- Preparation: Add compost or well-rotted manure to improve fertility
- Depth: Soil should be worked to at least 6-8 inches deep
- Nutrients: Adequate nitrogen early in growth cycle; phosphorus and potassium for bulb formation
Sunlight Needs
- Requirement: Full sun (minimum 6 hours direct sunlight)
- Optimal: 8-10 hours of direct sunlight daily
- Location: Choose a spot with no shade from other plants
- Importance: Insufficient light results in poor bulb formation
Water Requirements
- Early stage: Consistent moisture for establishment
- Growing season: 1 inch of water per week (including rainfall)
- Bulbing stage: Reduce watering when bulbs begin to form
- Pre-harvest: Stop watering 2-3 weeks before harvest
- Method: Drip irrigation preferred to keep foliage dry
Spacing Guidelines
- Between plants: 3-4 inches for average bulbs; 4-6 inches for larger varieties
- Between rows: 12-16 inches
- Planting depth: 1/2 inch deep for seeds; 1-2 inches for sets
- Bed configuration: Raised beds work well for better drainage
Climate Note: Onions are cool-season crops that can tolerate light frosts but grow best when temperatures are between 55-75°F (13-24°C). Extremely hot weather can affect bulb development.
Planting Calendar and Seasons
Timing is critical when planting onions. Follow these guidelines based on your region and chosen planting method:
Planting Timeline
| Method | Northern Regions | Southern Regions |
|---|---|---|
| Seeds (indoor start) | January to February (10-12 weeks before last frost) |
September to October (for winter growing) |
| Seeds (direct sow) | April to May (after danger of hard freeze) |
October to January |
| Sets/Transplants | March to April (4-6 weeks before last frost) |
October to January |
| Harvest Period | July to September | April to June |
Regional Tip: Plant your onions 4-6 weeks before the last estimated spring freeze in your area. Your local agricultural extension service can provide specific timing for your region.
Seasonal Considerations
- Temperature triggers: Plant when soil temperatures reach at least 50°F (10°C)
- Day length awareness: Match your onion variety (short-day, long-day, or intermediate) to your region’s daylight patterns
- Fall planting option: In mild winter areas, plant in fall for spring harvest
- Succession planting: Stagger plantings 2-3 weeks apart for extended harvest
- Companion planting: Plant with compatible companions like carrots, beets, or lettuce, but avoid beans and peas
Step-by-Step Planting Guide
Prepare Your Soil
Remove weeds and debris. Work in 2-3 inches of compost or aged manure. For clay soils, add sand to improve drainage. Level the area and create raised rows if desired.
Add Fertilizer
Incorporate a balanced fertilizer (10-10-10) at a rate of 2-3 pounds per 100 square feet, or follow soil test recommendations. Onions are heavy feeders, especially of nitrogen.
Create Planting Furrows
For seeds: Make shallow furrows ¼ to ½ inch deep.
For sets: Make furrows 1-2 inches deep.
Space rows 12-16 inches apart.
Plant According to Method
For Seeds:
Sow seeds thinly in the furrow and cover with ¼ inch of fine soil. Water gently to avoid displacing seeds. When seedlings reach 3-4 inches tall, thin to 3-4 inches apart.
For Sets:
Place sets in the furrow 3-4 inches apart, with the pointed end facing up. Cover with soil, leaving just the tip exposed. Press soil firmly around each set.
For Transplants:
Plant seedlings 3-4 inches apart without bending the roots. Plant at the same depth they were growing previously. Water thoroughly after planting.
Mulch the Bed
After planting, add a thin layer of mulch (straw, dried grass clippings, or compost) to conserve moisture and suppress weeds. Keep mulch away from the developing bulbs.
Water Thoroughly
Water deeply after planting. Keep soil consistently moist but not soggy during the growing period. Use a soaker hose or drip irrigation if possible.
Pro Tip: To grow scallions (green onions), plant regular onion sets more densely (1-2 inches apart) and harvest when the green tops are 6-8 inches tall, before the bulbs fully form.
Care During Growing Season
Watering Schedule
- Provide 1 inch of water weekly
- Water deeply but infrequently
- Reduce watering when tops begin to yellow
- Stop watering completely 2-3 weeks before harvest
Weeding
- Keep area weed-free, especially during early growth
- Weed carefully to avoid damaging shallow roots
- Consider using a hoe for weeding between rows
- Apply additional mulch as needed to suppress weeds
Fertilizing
- Side-dress with nitrogen fertilizer when plants are 6 inches tall
- Apply additional nitrogen 3-4 weeks later
- Stop fertilizing when bulbs begin to form
- Avoid high-nitrogen fertilizers late in the season
Special Care
- Remove flower stalks (scapes) if they appear
- Gently brush soil away from bulb tops as they grow
- Avoid piling soil on developing bulbs
- Provide support for large-variety tops if needed
Bolting Prevention: If onions develop a flower stalk (bolt), they’re focusing energy on seed production rather than bulb growth. Remove these stalks immediately. To prevent bolting, avoid early planting in cold soil and choose bolt-resistant varieties.
Common Problems and Solutions
Pests
| Pest | Signs | Solution |
|---|---|---|
| Onion Thrips | Silvery specks on leaves, distorted growth | Insecticidal soap, neem oil, introduce beneficial insects |
| Onion Maggots | Wilting plants, rotting at base | Crop rotation, row covers, avoid planting where onions grew previously |
| Bulb Mites | Stunted growth, rotting bulbs | Avoid planting in overly wet areas, practice crop rotation |
Diseases
| Disease | Signs | Solution |
|---|---|---|
| Downy Mildew | Violet-gray fuzzy growth on leaves | Improve air circulation, avoid overhead watering, fungicide application |
| Neck Rot | Softening around neck during storage | Proper curing, avoid harvesting in wet conditions |
| White Rot | White fungal growth, yellowing leaves | Crop rotation, remove infected plants, solarize soil |
Growing Issues
| Problem | Possible Cause | Solution |
|---|---|---|
| Small Bulbs | Improper spacing, insufficient nutrients, wrong variety for region | Proper spacing, adequate fertilization, choose day-length appropriate varieties |
| Splitting Bulbs | Inconsistent watering, late-season nitrogen | Maintain even soil moisture, reduce nitrogen late in growth cycle |
| Bolting (Flowering) | Temperature fluctuations, early planting, mature sets | Plant at appropriate time, use fresh sets, remove flower stalks promptly |
| Thick Necks | Excessive nitrogen, improper variety, late planting | Reduce nitrogen, choose appropriate varieties, plant at recommended times |
Prevention Tip: Practice crop rotation, avoiding planting onions in the same location more than once every 3-4 years to reduce disease and pest pressure.
Harvesting Tips
When to Harvest
- For green onions/scallions: Harvest when stems are 6-8 inches tall
- For mature bulbs: Wait until 75-80% of the tops have fallen over naturally
- Timing indicators: Necks soften, foliage yellows and dries
- Weather considerations: Harvest during dry weather if possible
- Typical timeline: 90-120 days after planting for bulb onions (variety dependent)
Harvesting Process
Loosen the Soil
Use a garden fork to gently loosen soil around bulbs without damaging them.
Pull Carefully
Grasp the tops near the bulb and pull straight up with steady pressure. For stubborn bulbs, loosen more soil rather than pulling harder.
Shake Off Excess Soil
Gently remove loose soil, but don’t wash the bulbs if you plan to store them.
Leave Tops Attached
Keep the tops attached during the initial curing process. They contain nutrients that will be drawn into the bulb.
Harvest Tip: Don’t wait until all tops have fallen over, as some bulbs may begin to decay. When 75-80% have fallen, it’s time to harvest the entire crop.
Curing and Storage
Curing Process
Curing is essential for long-term storage. It dries the outer layers and seals the neck, preventing disease and rot.
Spread Out Onions
Lay harvested onions in a single layer in a warm, dry, well-ventilated location. Options include:
- On screens or racks under cover
- Hanging in mesh bags
- Braiding tops together and hanging (for soft-neck varieties)
Provide Air Circulation
Ensure good airflow around all bulbs. Don’t pile them up or store in closed containers during curing.
Maintain Proper Conditions
Ideal curing conditions:
- Temperature: 75-85°F (24-29°C)
- Humidity: 60-70%
- Duration: 2-3 weeks until necks are completely dry
Trim for Storage
After curing, trim tops to 1 inch above the bulb. Trim roots close to the base. Remove any loose, flaky outer skin, but don’t peel too much as this protects the bulb.
Storage Methods
Ideal Storage Conditions
- Temperature: 32-40°F (0-4°C)
- Humidity: 65-70%
- Air circulation: Good airflow around bulbs
- Light: Dark or minimal light
- Avoid freezing: Temperatures below 32°F can damage bulbs
Storage Options
- Mesh bags: Hang in a cool, dry location
- Shallow crates: Line with newspaper and don’t stack too deep
- Pantyhose method: Place individual onions in pantyhose with knots between each one
- Braiding: Traditional method for soft-neck varieties
- Repurposed egg cartons: Good for separating individual bulbs
Storage Duration: Properly cured and stored onions can last 3-6 months or even longer, depending on the variety. Sweet onions generally have shorter storage lives (1-2 months) than pungent varieties (up to 8 months).
Checking Stored Onions
- Inspect stored onions regularly for signs of sprouting or rot
- Remove any onions that show signs of decay immediately
- Use softer or sprouting onions first
- Consider freezing, dehydrating, or pickling onions that won’t store well
Conclusion
Growing onions can be a rewarding experience for any gardener. With proper planning, care, and patience, you can harvest flavorful onions that will enhance your cooking for months to come. Remember that each garden is different, and you may need to adjust techniques based on your specific climate and soil conditions.
Keep a garden journal to track your onion-growing experience, noting which varieties performed best in your area and any challenges you encountered. This information will be invaluable for future growing seasons.
Final Tip: Save some of your best onions for replanting to start a self-sustaining cycle of onion production. With each season, you’ll become more attuned to the needs of your onion crop and develop a deeper understanding of what works best in your garden. Happy Gardening…
