Onions are a kitchen staple that's surprisingly easy to grow—once you understand their unique day-length requirements. This guide covers everything from variety selection to long-term storage.
Understanding Day Length
Onions form bulbs based on day length. This is the most important factor in choosing varieties:
- Short-day onions: Bulb when days reach 10-12 hours (southern states)
- Intermediate-day: Bulb at 12-14 hours (middle states)
- Long-day onions: Bulb at 14-16 hours (northern states)
Growing the wrong type for your latitude = small bulbs or no bulbs!
Planting Options
From Sets (Easiest)
- Small bulbs planted directly in spring
- Fastest to harvest
- More prone to bolting
- Limited variety selection
- Best for beginners
From Transplants
- Pencil-thick seedlings
- Best combination of ease and quality
- Buy from local nurseries or order online
- Plant as soon as ground can be worked
From Seed (Best Selection)
- Most varieties available
- Start indoors 8-10 weeks before transplanting
- Trim tops to 4" to strengthen
- Best for experienced growers
🧅 Size Matters for Sets
Choose smaller sets (dime-sized). Larger sets are more likely to bolt. If sets have started sprouting, they're old—find fresher ones.
Planting and Growing
Site and Soil
- Full sun (6+ hours)
- Loose, well-drained soil
- pH 6.0-7.0
- Rich in organic matter
- Raised beds work great
Planting
- Space 4-6 inches apart (closer for scallions)
- Rows 12-18 inches apart
- Plant sets 1" deep, pointy end up
- Transplants at same depth as in pot
Care
- Keep consistently moist (shallow roots!)
- Weed carefully (fragile roots)
- Mulch to retain moisture
- Fertilize monthly with nitrogen-rich feed
- Stop watering when tops begin to fall
Harvest and Curing
When to Harvest
- Tops fall over and begin to dry
- Outer skins are papery
- Usually mid to late summer
- Don't wait too long—soft necks rot
Curing for Storage
- Pull onions and lay in single layer
- Cure in warm, dry, airy location
- Protect from direct sun and rain
- Cure 2-4 weeks until necks are completely dry
- Trim roots and tops to 1 inch
Storage
- Store in cool (35-50°F), dry, dark location
- Good airflow essential
- Mesh bags or braiding work well
- Check regularly, remove any soft ones
- Storage onions can last 6-12 months
Best Storage Varieties
- Yellow onions: Copra, Patterson, Stuttgarter
- Red onions: Red Zeppelin, Redwing
- White: Generally don't store as long
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