You know that half-sprouted onion sitting in your kitchen right now? I used to toss those without a second thought. Then I tried something crazy - stuck one in dirt just to see what’d happen. Three months later, I harvested eight fresh onions from that single bulb. Mind blowing, right? Let's cut through the garden myths and talk real dirt about how do onions grow from an onion.
Exactly What Happens When You Plant an Onion Bulb
It starts with that little green shoot poking out. See, onions are biennial plants. What we eat is actually Year 1 growth. When you plant a mature bulb, it thinks: "Season two! Time to flower!" But here’s the clever part - we interrupt that cycle to make new bulbs.
From that sprout, new roots explode downward (about 2-3 inches deep) while leaves shoot upward. Each leaf layer wraps around the developing bulb underground. I’ve found grocery store onions work 60% of the time, but nursery sets give near 100% success.
Key Insight: The outer layers of your original onion don’t become new onions - they decay to feed the sprouts. New bulbs form around the base plate where roots emerge. That plate is the command center.
Step-by-Step: How Onions Grow From an Onion
- Prep your bulb: Use firm onions with visible sprouts. Peel papery skin until you see root buds
- Root awakening: Soak base plate in water 2-3 days until white roots appear (don’t submerge whole onion!)
- Planting depth: Bury only the roots and base plate. Leave sprout completely exposed
- The split: After 2 weeks, the original bulb softens as sprouts multiply
- Bulb formation: Each sprout develops its own layered bulb underground
- Harvest signs: When tops yellow and flop over, new onions are ready
Last spring I got impatient and dug one up early. Big mistake - ended up with scallions instead of bulbs. Timing is everything when learning how onions grow from an onion.
Soil Secrets for Maximum Bulb Production
Onions are picky eaters. Mine completely stalled in clay soil until I amended it. The magic formula:
| Soil Component | Why It Matters | My Recommended Mix |
|---|---|---|
| Nitrogen | Leaf growth = bigger bulbs | Blood meal or composted manure |
| Phosphorus | Root development | Bone meal at planting time |
| Sandy Loam | Drainage prevents rot | 30% sand, 60% soil, 10% compost |
| pH Level | Affects nutrient uptake | 6.0-6.8 (test kit costs $12) |
Space bulbs 4-6 inches apart. Crowding caused half my crop to stay marble-sized last season. Watering tip: Give them 1 inch weekly, but stop when tops yellow to prevent rot. I killed a whole row by overwatering during bulb maturation - smelled like a compost disaster.
Which Onion Types Regrow Best?
Not all onions play nice. Through trial and error (mostly errors):
| Onion Type | Regrow Success Rate | Taste Notes | My Verdict |
|---|---|---|---|
| Yellow Storage Onions | 85% | Classic pungent flavor | Winner for reliability |
| Red Onions | 70% | Milder, great raw | Good but slower |
| White Sweet Onions | 40% | Mild, low sulfur | Finicky - needs perfect conditions |
| Shallots | 95% | Subtle garlic notes | Easiest multiplier! |
| Green Onion (Scallion) | 100% in water | Mild onion flavor | Great for beginners |
Fun fact: Those sprouting grocery store onions are usually long-day varieties. If you live below 35° latitude, try short-day types like Georgia Sweet instead. I learned this after my New Mexico onions bolted immediately.
Your Month-by-Month Growth Timeline
Patience pays off. From my garden journal:
| Timeline | What's Happening Underground | Your Action Items |
|---|---|---|
| Week 1-2 | Root establishment (no visible growth) | Water lightly daily |
| Week 3-4 | Sprouts grow 2-3 inches | Apply nitrogen fertilizer |
| Month 2 | Original bulb softens and decomposes | Weed carefully - shallow roots! |
| Month 3 | New bulbs form (marble size) | Reduce watering frequency |
| Month 4 | Bulbs enlarge rapidly | Push soil away from shoulders |
| Month 5 | Tops yellow and fall over | Stop watering completely |
Harvest on a dry morning. Cure onions in shaded breeze for 2 weeks before storage. My first batch molded because I skipped curing - don't be like me.
Troubleshooting Your Onion Crop
When things go wrong (they will):
Why are my onions all tops no bulbs?
Likely causes: Too much nitrogen after bulb formation began, overcrowding, or insufficient sunlight. Onions need 6+ hours of direct sun.
White fuzz on roots?
Root rot from soggy soil. Improve drainage immediately. I lost 60% of my crop to this during a rainy spell.
Flowers appearing?
Bolting! Caused by temperature swings. Snip flower stalks immediately. Bolted onions won't store well but can be used fresh.
Water vs Soil: Unexpected Results
You can regrow onions in water - but should you? My comparison test:
| Method | Growth Speed | Bulb Size | Longevity |
|---|---|---|---|
| Water Only | Faster initial sprouting | Small (scallion size) | Dies after 8 weeks |
| Soil Planting | Slower start | Full-sized bulbs | Produces for months |
Water works for quick green tops, but soil is essential for real bulbs. That Instagram post showing giant onions growing in a jar? Total myth. Real bulb formation requires soil nutrients.
Advanced Tips From My Failures
- The neck rot disaster: Water trapped between leaves invites fungus. Water at soil level only
- Bolted batch: Plant when temps stay consistently above 40°F (4°C)
- Stunted bulbs: Thin to 4-inch spacing - crowded onions compete
- Pungent instead of sweet: Stress increases sulfur compounds. Consistent watering = milder flavor
Companion planting helps too. I grow carrots between onions - their roots occupy different depths and deter each other's pests. Avoid planting near beans or peas though.
Harvesting Secrets Most Guides Miss
Timing is delicate. Harvest too early = small bulbs. Too late = split or rotten centers:
- When half the tops have fallen over naturally
- Gently lift bulbs with a garden fork (never pull!)
- Cure in single layer for 14 days in ventilated shade
- Trim roots to 1/2 inch and cut tops to 1 inch
Store in mesh bags in a cool dark place. My garage shelf keeps them 6+ months. Refrigeration causes starch conversion = mushy texture.
Your Burning Questions Answered
Can you regrow onions indefinitely?
Technically yes, but vigor declines after 3 generations. I refresh my stock every two years.
Do I need special organic onions?
Conventional store onions often have growth inhibitors. Organic works better, but nursery sets are most reliable.
Why did my onion grow flowers instead of bulbs?
Temperature fluctuations tricked it into thinking it completed Year 1. Maintain consistent conditions.
How many onions grow from one bulb?
Typically 6-8 new bulbs around the original base plate spacing.
Can this work indoors?
Possible with grow lights. But bulbs will be smaller without natural temperature cycles.
Final Reality Check
Is this actually worth it? Financially - barely. You'll spend $3 on soil to grow $2 worth of onions. But the satisfaction? Priceless. Seeing that first cluster of new bulbs forming taught me more about plant life cycles than any textbook.
The real magic happens underground. When you understand how do onions grow from an onion, you realize every bulb is a biological time capsule. Those layers contain an entire growth season - and the potential for dozens more. Now if you'll excuse me, I've got some sprouting shallots begging for dirt.
Comment