Learning how to grow onions from kitchen scraps offers an efficient, sustainable way to reduce waste while enjoying a continuous supply of fresh onions. The process is simple, requiring minimal space, basic materials, and little gardening experience. Whether you're working with green onions or bulb onions, you can regenerate them into new plants by reusing the leftover bases you usually discard.
This method appeals to gardeners and sustainability enthusiasts alike. It’s budget-friendly, educational, and rewarding, especially when fresh onion greens start sprouting on your windowsill or balcony. In this guide, you'll find practical, detailed instructions on how to grow onions from kitchen scraps using both water and soil, along with essential care tips, harvesting advice, and troubleshooting support.
Why Growing Onions from Kitchen Scraps Works
Onions are biennial plants that grow from bulbs. When you slice an onion and leave the root end intact, you're preserving the part of the plant that can regrow. The basal plate—the flat, root-bearing portion at the bottom of the bulb—contains the genetic material and energy stores needed for the plant to send out new shoots and roots.
When placed in the right conditions, that small disc of onion left from meal prep can regenerate, giving rise to green onion tops or even full bulbs over time.
Types of Onions That Can Be Grown from Scraps
When exploring how to grow onions from kitchen scraps, it’s helpful to understand which onion varieties lend themselves best to regeneration:
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Green onions (scallions) – These are the easiest and fastest to regrow from scraps. The roots readily reestablish in water or soil.
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Bulb onions (red, white, yellow) – These can regrow if the root end is intact. You may not always get a full bulb, but you can certainly harvest greens and possibly develop dividing bulbs.
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Shallots – Like bulb onions, shallots can regrow from scraps and form clusters over time.
Step-by-Step Guide: How to Grow Onions from Kitchen Scraps
Step 1: Save the Right Part of the Onion
The first step in learning how to grow onions from kitchen scraps is saving the part of the onion capable of regrowth.
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Cut the onion about 1 to 2 inches above the root base.
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Make sure the basal plate is intact and has visible root stubs.
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Discard any outer layers that appear slimy or damaged.
Set the base aside for immediate planting or store it in a cool, dry area for up to 2–3 days if needed.
Step 2: Choose a Growing Method – Water or Soil
There are two popular ways to regrow onions from scraps: in water or directly in soil. Each has its own benefits depending on your space and preference.
Method 1: Regrowing Onions in Water
This method is ideal for green onions or for getting a quick start before transferring to soil.
Materials:
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A small glass or jar
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Clean water
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Toothpicks (optional)
Instructions:
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Place the onion root end in a jar with the cut side facing upward.
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Add water until it just covers the roots. Avoid submerging the entire base.
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Optionally, insert toothpicks around the side of the base to suspend it above the water line if the jar is too narrow.
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Place the container in a sunny windowsill.
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Change the water every 2–3 days to prevent bacterial growth.
What to Expect:
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New green shoots will begin to emerge within 3–5 days.
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Roots will start extending downward, signaling successful regeneration.
Once the shoots reach 4–6 inches, you can harvest the green tops or transfer the base to soil for further development.
Method 2: Regrowing Onions in Soil
This is the preferred method if your goal is to regrow full bulbs or sustain long-term growth.
Materials:
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Onion root base
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Pot or garden bed with well-draining soil
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Watering can or spray bottle
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Compost or organic fertilizer (optional)
Instructions:
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Choose a container with drainage holes or select a sunny spot in your garden.
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Fill it with loose, well-draining soil rich in organic matter.
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Bury the onion base root-side down, about 1 inch deep. Leave the top exposed.
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Water thoroughly to settle the soil around the base.
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Place in full sun and keep the soil consistently moist, not soggy.
What to Expect:
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Shoots should appear within 1–2 weeks.
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Roots will anchor the plant within 7–10 days.
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Over time, the plant may divide into multiple bulbs.
You can grow onions this way indoors or outdoors depending on climate and space.
Step 3: Caring for Regrowing Onion Plants
Whether you start in water or soil, proper care ensures healthy regrowth.
Sunlight Needs:
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Onions prefer full sunlight—at least 6–8 hours daily.
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A bright windowsill, balcony, or patio works well for containers.
Watering:
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In water: Maintain the correct level, change it frequently.
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In soil: Keep the soil evenly moist but not waterlogged. Overwatering can lead to rot.
Temperature:
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Onions grow best between 55°F and 75°F.
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Avoid extreme cold or heat unless the variety is suited to such conditions.
Fertilizing:
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For better bulb development, apply a balanced organic fertilizer every few weeks.
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Compost or worm castings can be gently worked into the topsoil.
Pruning Green Tops:
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Once green shoots are 6–8 inches tall, you can trim them with clean scissors.
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Cut only what you need and leave at least 2 inches of shoot to allow regrowth.
How to Encourage Bulb Formation
If you’re interested in growing full-size onions, the process is more gradual and requires attention to spacing, feeding, and seasonal timing.
Tips to Encourage Bulb Growth:
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Space: If planting multiple onion scraps, ensure they are 4–6 inches apart.
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Day Length: Onion bulb formation depends on daylight hours. Use a variety suited to your region’s day length (short-day, intermediate, or long-day onions).
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Feeding: Add phosphorus-rich fertilizer to support root and bulb development.
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Thinning: As the plant divides, thin weaker shoots to allow stronger bulbs to develop.
Keep expectations realistic. While growing onions from kitchen scraps may not always produce supermarket-sized bulbs, you can certainly harvest usable bulbs and greens with care and time.
Common Problems and How to Fix Them
1. Rotting Onion Base
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Cause: Excess moisture, stagnant water, or poor drainage.
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Fix: Reduce watering frequency, improve drainage, and use fresh water in hydroponic setups.
2. Mold or Fungus
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Cause: High humidity or poor air circulation.
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Fix: Increase airflow around the plant, avoid crowding, and use sterile containers.
3. No New Growth
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Cause: The onion base may be too old or damaged.
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Fix: Try another base with visible root stubs and a firm, healthy texture.
4. Weak or Leggy Shoots
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Cause: Insufficient light.
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Fix: Move the plant to a sunnier location or supplement with grow lights.
Harvesting and Using Regrown Onions
Depending on your growing method and onion type, you’ll see results within days or weeks.
Green Onions:
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Snip the green shoots as needed once they’re a few inches tall.
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They will regrow multiple times from the same base.
Bulb Onions:
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Harvest when the leaves begin to yellow and fall over.
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Gently lift the bulb, cure it in a dry, ventilated area for 1–2 weeks, and store it in a cool, dark place.
Shallots or Dividing Bulbs:
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Separate the new bulbs from the original root and replant or use them in cooking.
Scaling Up: From Windowsill to Garden
Once you’ve mastered how to grow onions from kitchen scraps on a small scale, consider expanding. Collect multiple scraps from your cooking routine or local restaurants. Use egg cartons or seed trays to pre-root multiple bases before transferring them into garden beds or raised containers.
Over time, you can build a self-sustaining onion patch fueled entirely by kitchen waste.
Final Thoughts
Understanding how to grow onions from kitchen scraps opens the door to sustainable, low-cost gardening. With minimal effort, you can transform everyday kitchen waste into thriving green shoots and even full onion bulbs. Whether you're planting on a sunny windowsill, balcony, or backyard garden, the methods shared here will help you make the most of your onion remnants.
Through simple practices like saving root ends, choosing the right growing medium, and maintaining proper care, you can enjoy a renewable source of fresh onions year-round. It’s a practical, satisfying project that turns waste into nourishment—and a small way to reconnect with nature, right from your own home.