Grow Onions from Sprouted Onions: Complete Step-by-Step Guide

Yes, you can successfully grow a new onion from a sprouted onion by cutting off the root end with 1-2 inches of onion remaining, allowing it to dry for 24 hours, then planting it 1 inch deep in well-draining soil with the green sprouts facing upward. Water regularly and harvest green onion shoots in 7-10 days, with full bulb development taking 3-4 months.

Have you discovered sprouted onions languishing in your pantry? Instead of tossing them, you've got a golden opportunity to grow fresh onions at home with minimal effort. This practical guide reveals exactly how to transform those seemingly wasted sprouted onions into a continuous supply of fresh green onions and eventually full-sized bulbs—saving you money while reducing food waste.

Why Sprouted Onions Make Perfect Candidates for Regrowing

When onions begin sprouting, they're actually activating their natural growth cycle. That green shoot emerging from the top isn't a sign of spoilage—it's the onion's survival mechanism kicking in. According to research from the University of California Agriculture and Natural Resources, onions store energy in their bulb specifically to support new growth when conditions become favorable.

Unlike many vegetables that require seeds or cuttings, sprouted onions come pre-packaged with everything needed for successful regrowth. The existing root base provides immediate anchoring, while the stored nutrients in the bulb give your new plant a significant head start compared to growing from seed.

Selecting the Right Sprouted Onion for Regrowth

Not all sprouted onions will successfully regrow. Follow these selection criteria to ensure success:

• Firm bulb base - Avoid onions with soft, mushy, or moldy spots at the root end
• Healthy green shoots - Look for vibrant green sprouts (yellowing indicates stress)
• Minimal sprouting - Best candidates have sprouts under 3 inches tall
• Intact root plate - The bottom where roots emerge should be undamaged

Discard any onions showing signs of rot, mold, or excessive softness. Remember that sweet onions typically have shorter storage lives and may not regrow as successfully as storage varieties like yellow onions or red onions.

Step-by-Step: Preparing Your Sprouted Onion for Planting

Proper preparation significantly increases your success rate. Follow these precise steps:

1. Cut off the root end with 1-2 inches of onion remaining (discard the top portion)
2. Place the cut sections on a paper towel in a well-ventilated area
3. Allow to dry for 24 hours to form a protective callus over the cut surface
4. Optional: Dip the cut side in rooting hormone powder for faster establishment
5. Inspect before planting—discard any showing signs of rot during drying

This drying period is crucial—it prevents immediate rotting when planted in moist soil. Research from the USDA National Institute of Food and Agriculture confirms that proper curing of cut surfaces significantly improves success rates for regrowing bulb vegetables.

Planting Methods: Soil vs. Water Regrowth

You have two effective options for growing your sprouted onion. Each has advantages depending on your goals:

Method	Best For	Time to First Harvest	Long-Term Potential
Soil Planting	Full bulb development	3-4 months for bulbs	Complete life cycle possible
Water Regrowth	Continuous green onion harvest	7-10 days for greens	Limited to green shoots only

Soil Planting Instructions

For complete bulb development:

• Use well-draining potting mix in containers with drainage holes
• Plant with the green sprouts facing upward, 1 inch deep
• Space plants 4-6 inches apart in garden beds
• Water thoroughly after planting, then maintain consistent moisture
• Place in location receiving 6-8 hours of direct sunlight daily

Water Regrowth Method

For continuous green onion production:

• Place prepared onion base in shallow dish with ½ inch of water
• Ensure water covers the root end but not the green sprouts
• Change water every 2-3 days to prevent bacterial growth
• Position in bright indirect light (south-facing windows work well)
• Harvest green shoots when 6-8 inches tall, leaving 2 inches to regrow

Onion Growth Timeline: What to Expect Week by Week

Understanding the growth progression helps set realistic expectations. Based on data from Cornell University's gardening extension, here's the typical development pattern:

• Days 1-7: Root development begins; green shoots grow 1-2 inches
• Weeks 2-3: Established root system; green shoots reach 4-6 inches
• Weeks 4-6: First harvest of green onions possible; bulb begins forming
• Months 2-3: Bulb development accelerates; requires consistent watering
• Months 3-4: Bulb reaches full size; tops begin to yellow and fall over

Temperature significantly affects growth speed. Onions grow most rapidly between 55-75°F (13-24°C). Below 50°F (10°C), growth slows considerably, while temperatures above 80°F (27°C) can cause premature bolting.

Care Requirements for Thriving Onion Plants

Proper care ensures healthy growth and maximum yield:

Watering Schedule

Onions need consistent moisture but hate soggy conditions. Water when the top inch of soil feels dry, providing about 1 inch of water weekly. During bulb formation (weeks 6-10), increase to 1.5 inches weekly. Reduce watering as harvest approaches to prevent rot.

Fertilization Needs

Apply balanced fertilizer (10-10-10) every 3-4 weeks. Onions particularly benefit from nitrogen during early growth, then need more phosphorus and potassium as bulbs develop. Avoid high-nitrogen fertilizers late in the season, which can delay bulb formation.

Sunlight Requirements

Onions require 6-8 hours of direct sunlight daily for optimal growth. In extremely hot climates, afternoon shade can prevent stress. Rotate containers regularly if growing indoors to ensure even light exposure.

Harvesting Your Homegrown Onions

Knowing when and how to harvest makes all the difference in flavor and storage potential:

• Green onions: Harvest when shoots reach 6-8 inches tall, cutting 2 inches above the bulb
• Scallions: Harvest when stems are pencil-thick, typically 60-80 days after planting
• Full bulbs: Wait until tops yellow and fall over naturally (usually 100-120 days)

For full bulbs, carefully lift plants from soil and cure them in a warm, dry, well-ventilated area for 2-3 weeks before storing. Properly cured onions can store for 3-5 months in cool, dry conditions.

Troubleshooting Common Growing Problems

Even with proper care, issues may arise. Here's how to address them:

Yellowing Leaves

Possible causes: Overwatering, nitrogen deficiency, or natural maturation
Solution: Check soil moisture; if excessive, reduce watering. If uniform yellowing occurs early, apply nitrogen-rich fertilizer.

Soft or Rotting Bulbs

Possible causes: Poor drainage, fungal infection, or planting too deep
Solution: Ensure proper drainage; plant at correct depth (1 inch); avoid overhead watering.

Stunted Growth

Possible causes: Crowded plants, nutrient deficiency, or insufficient light
Solution: Thin plants to proper spacing; apply balanced fertilizer; increase light exposure.

Maximizing Your Onion Harvest: Pro Tips

Implement these advanced techniques to boost your yield:

• Plant multiple batches 2-3 weeks apart for continuous harvest
• Add crushed eggshells to planting holes for calcium and pest deterrence
• Use mulch to maintain consistent soil moisture and temperature
• Rotate planting locations annually to prevent disease buildup
• Harvest green shoots in the morning when flavor compounds are most concentrated

Remember that onions grown from sprouted bulbs may not develop as large as those grown from seed or sets, but they provide excellent green onions and respectable bulbs with proper care. The University of Minnesota Extension confirms that regrown onions maintain comparable nutritional value to store-bought varieties.

Frequently Asked Questions

Can I grow onions from grocery store sprouted onions?
Yes, most grocery store onions will successfully regrow. However, some commercial onions are treated with sprout inhibitors. Organic onions typically sprout more readily and make better candidates for regrowth.

How many times can I regrow the same onion?
You can typically harvest green shoots 3-4 times from the same onion base before the bulb's energy reserves deplete. For continuous production, plant multiple onions in succession.

Why are my regrown onions smaller than store-bought ones?
Homegrown onions often develop smaller bulbs because they lack the ideal growing conditions of commercial farms. Focus on harvesting the flavorful green shoots, which develop quickly regardless of bulb size.

Can I grow onions indoors year-round?
Yes, onions grow well indoors with proper light. Use a south-facing window or supplement with grow lights providing 14-16 hours of light daily. Indoor temperatures between 60-75°F (15-24°C) are ideal.

By following these detailed steps, you'll transform what would have been food waste into a continuous supply of fresh onions. Whether you're harvesting green shoots for salads and garnishes or growing full bulbs for cooking, this simple technique puts you in control of your food supply while reducing kitchen waste. Start with just one sprouted onion today and enjoy the satisfaction of watching your pantry staple come back to life.