Planting onions from seed is a rewarding venture for home gardeners and commercial growers alike. Onions (Allium cepa) are classified by the amount of daylight they need to form bulbs, generally divided into short-day, intermediate-day, and long-day varieties. Before you begin, it’s vital to understand your region’s latitude and daylight hours, as these factors are key to successfully growing healthy onion bulbs. Short-day varieties are typically best for southern latitudes, long-day types thrive in the north, and intermediate-day onions can suit those in between or who want to experiment at nearby latitudes.

1. Seed Starting and Soil Preparation
If you plan to grow onions from seed, timing is everything. Most growers start seeds indoors about 8–10 weeks before the last spring frost date. Use a high-quality seed starting mix and provide ample light—ideally, 12–14 hours per day under grow lights. Keep the soil consistently moist but never waterlogged. Once seedlings reach about three inches tall, trim the tops slightly to encourage stronger root growth. Outdoors, prepare a well-draining bed rich in organic matter—onions thrive in loose, fertile soil with a pH between 6.0 and 6.8. Work in compost or aged manure to boost soil nutrients and structure.

2. Transplanting and Spacing
When the soil temperature rises above 50°F (10°C), you can harden off and transplant your onion seedlings outdoors. Gradually introduce them to direct sunlight and outdoor conditions over a week. Space onion plants 4–6 inches apart in rows 12–18 inches apart, ensuring they have enough room to form large bulbs. Onions have shallow root systems, so consistent irrigation—about 1 inch of water per week—is crucial, especially in hot weather. Mulching can help conserve moisture and suppress weeds, which compete for the onions’ limited root space.

3. Fertilization and Care
Onions are relatively heavy feeders, requiring steady access to nitrogen and other nutrients throughout the growing season. An all-purpose fertilizer or a balanced organic blend works well; consider side-dressing with compost or nitrogen fertilizer every few weeks if growth stalls. Monitor for pests like thrips and diseases like fungal rot, and practice crop rotation to avoid soil-borne issues. As bulbs mature and tops begin to flop over, it’s a signal that they are nearing harvest. Cure harvested onions in a dry, well-ventilated area for a couple of weeks to prolong storage life.

4. Day-Length Categories and Variety Selection

• Short-Day Onions (latitudes roughly 25°–35°) form bulbs when they receive about 10–12 hours of daylight. They typically mature earlier and are well-suited for warm southern regions. Some short-day onions can be grown successfully in slightly higher latitudes if started early or provided with optimal growing conditions.
• Intermediate-Day Onions (latitudes roughly 32°–40°) need about 12–14 hours of daylight to bulb. They are highly adaptable, making them a good choice for many mid-latitude gardeners or those who want overlap with nearby latitude zones.
• Long-Day Onions (latitudes roughly 37°–47° and above) initiate bulbing with 14–16 hours of daylight. They excel in northern climates with extended summer days, producing large, sweet bulbs in cooler conditions.

Below are 20 recommended varieties for each day-length category, including some that can adapt to nearby latitudes:

20 Top Short-Day Onion Varieties

(Best for southern regions or latitudes around 25°–35°, with some adaptable slightly north if conditions allow)

1. Texas 1015Y – Classic sweet, mild flavor
2. Granex Yellow (Vidalia Type) – Famous for sweet taste
3. White Bermuda – Early-maturing white onion
4. Red Creole – Spicy, good for Cajun cooking
5. Texas Early White – Crisp, white flesh
6. Savannah Sweet – Large, sweet bulbs
7. Crystal Wax (White Wax) – Mild, great for salads
8. Yellow Granex – Juicy, mild flavor
9. Red Burgundy – Vibrant red skin, mild taste
10. Rio Grande – Medium-large, good keeper
11. Southern Belle Red – Attractive red globe
12. White Granex – Sweet white onion, good for fresh use
13. Texas Legend – Improved Texas-type variety
14. Grano 502 – Classic short-day variety, good yield
15. Bella Vista – Uniform bulbs, mild flavor
16. Early Red Sweet – Sweet, matures quickly
17. Red Granex – Sweet red onion, good fresh
18. Carzalia Sweet – Known for large, mild bulbs
19. Yellow Creole – Good storage, robust flavor
20. Tropicana – Heat-tolerant, mild sweet onion

20 Top Intermediate-Day Onion Varieties

(Typically suited for latitudes around 32°–40°, can adapt to some adjacent regions)

1. Candy – Popular, large bulbs, sweet flavor
2. Red Candy Apple – Sweet red onion, good fresh
3. Super Star (Supa Star) – White, mild, excellent yields
4. Sierra Blanca – White, crisp, mild
5. Sterling – Pure white skin, great flavor
6. Expression – Uniform bulbs, disease-resistant
7. Cimarron – Strong red variety, stores well
8. Candy Ann – Early, high yields, sweet taste
9. Candy Rubies – Dark red color, sweet
10. Scout – Yellow onion, uniform size
11. Blush – Unique pinkish hue, mild flavor
12. Sedona – Good storage onion, firm texture
13. Red Torpedo (Tropea type) – Elongated, sweet red
14. Cabernet – Dark red globe, well-adapted
15. Candy White – Sister variety to Candy, mild
16. Candy Apple – Another sweet red selection
17. Stockton Yellow – Good for fresh markets
18. Stockton Red – Firm red onion, good storing
19. Bella Rosa – Pinkish-red onion, mild taste
20. Redwing – Often classed as intermediate to long-day, reliable performer

20 Top Long-Day Onion Varieties

(Ideal for northern latitudes around 37°–47°+, but some can perform in lower latitudes with the right conditions)

1. Walla Walla – Renowned sweet onion, large bulbs
2. Ailsa Craig – Giant onion, mild flavor
3. Copra – Excellent storage, yellow onion
4. Patterson – Similar to Copra, stores well
5. Yellow Sweet Spanish – Large, mildly sweet bulbs
6. Ringmaster – Classic white bulb, used for onion rings
7. Red Zeppelin – Deep red, stores well
8. White Sweet Spanish – Mild, large white onion
9. Stuttgarter – Popular heirloom, good keeper
10. New York Early – Hardy, reliable yields
11. Dakota Tears – Very flavorful, stores excellently
12. Redwing – Can also fit intermediate-day zones, robust red color
13. Brunswick – Flat-shaped, traditional European variety
14. Highlander – Early maturing, good storage
15. Southport Red Globe – Classic red onion, strong flavor
16. Southport White Globe – Firm, white onion, stores well
17. Southport Yellow Globe – Heirloom with good storage
18. Yellow of Parma – Italian variety, large bulbs
19. Alisa F1 – Hybrid with huge bulbs, mild flavor
20. Candy (in northern trials) – Some growers find success at higher latitudes.

Successful onion growing hinges on matching varieties to your climate’s day length, plus diligent care from seed to harvest. By starting seeds indoors, transplanting them into well-prepared soil, and consistently providing water and nutrients, you can reap a bountiful harvest of crisp, flavorful bulbs. Keep an eye on the unique qualities of each variety—some excel in sweetness, others in storage life—and don’t be afraid to experiment with onions that can straddle nearby day-length boundaries. With thoughtful planning and proper cultivation, you’ll enjoy homegrown onions that elevate every dish and reward your gardening efforts.