Kitchen-Counter Method
Can You Grow an Onion From an Onion? The Honest Answer
By Ada Jones · Updated October 2026 · Figures checked against extension and grower sources linked in the text
Yes, you can grow an onion from an onion that’s already sprouted, or from an onion base/scraps with the roots attached — but set your expectations honestly: you’ll usually get green shoots quickly and sometimes a cluster of small bulbs, rarely a full-size storage onion. Onions are biennials, so a bulb that has already sprouted is heading toward flowering, not toward making a bigger bulb.
Growing From an Onion at a Glance
| Quick Fact | What to Know |
|---|---|
| What you’ll get | Green shoots quickly; sometimes a cluster of small bulbs; rarely a full storage onion |
| Why | Onions are biennials — a sprouted bulb is heading toward flowering, not bulking up |
| Planting depth | At least 6 inches (15 cm) of loose, well-draining soil, roots covered |
| Light | Full sun |
| Time to shoots | Leaves within 1 to 2 weeks |
| Best use | Greens for the kitchen, or an experiment, not a reliable storage crop |
Sources: Grow Organic.
How to Grow an Onion From an Onion, Step by Step
- Choose your starting piece. Either a whole onion that has already sprouted a green shoot, or cut the bottom third off a fresh onion, keeping the roots attached. Use the remaining two-thirds in your cooking.
- Trim it up. Remove papery outer layers and any dried-up roots from the base.
- Root it in water first if you like. Many home growers set the onion base in a shallow dish or bottle with the root end just touching water. New roots and shoots typically appear within a few days, with visible growth by about nine days.
- Plant it. Once rooted (or straight away if using a sprouted whole onion), plant in a container with at least 6 inches (15 cm) of loose, well-draining soil. Cover the roots and the base; keep the shoot upright and don’t bury it too deep.
- Water evenly and give it full sun. Expect leaves within one to two weeks; you can clip these as green onions as they grow.
- Separate clusters once they have roots. If multiple shoots develop from one base, you can gently pull them apart once each has its own roots and replant them a few inches apart to let them size up individually.
Real example: a home grower documented on video planting a single onion bottom, separating the shoots at about day 40 and replanting them, then starting harvest around day 120 and finishing roughly 30 days later with 21 bulbs from that one base. The same grower found that an unseparated cluster produced much smaller onions than the separated shoots, and that a whole bulb planted alongside the experiment grew faster and bigger than either. This is one grower’s documented result, not a controlled trial, but it’s a useful benchmark for what separating shoots can do.
How Many Onions Will Grow From Planting One Onion?
Don’t expect a predictable number. A cluster of shoots from one sprouted base commonly separates into anywhere from a few to a dozen or more small bulbs, depending entirely on how many viable shoots form and how carefully they’re separated and spaced afterward. The 21-bulb result above is a strong outcome from careful separation and replanting, not a typical baseline.
Why Won’t It Form a Full-Size Bulb?
This is the single biggest misunderstanding in this whole topic, so it’s worth saying plainly: an onion is a biennial. In its first year it stores energy in the bulb; in its second year (which is what you’re planting when you use a sprouted grocery-store onion) its biological goal is to flower and set seed, not to build another large bulb. Grow Organic’s guide makes the same point — these plants can grow, but they don’t always reach full-size bulbs, and starting from seed or sets gives far more reliable results if a storage crop is your goal. Treat this method as a way to get free greens or run an experiment, not as your main onion-growing strategy. For a reliable storage crop, see growing from sets or growing from seed.
Frequently Asked Questions
Can you grow onions from grocery-store onions?
Yes, if it has sprouted, but expect greens or a few small bulbs rather than a full-size storage onion. Seed or sets give far more reliable results for a real crop.
Do you need seeds to grow onions from an onion?
No. Planting a sprouted onion, its root end, or a kitchen scrap with roots attached works without any seed, though results are less predictable than growing from seed or sets.
How deep do you plant an onion base?
At least 6 inches (15 cm) of loose soil, with the roots covered and the shoot kept upright above the surface.
Can you grow onions from scraps in water first?
Yes — rooting the base in water before potting it up is a common home technique and gives the roots a head start before the move to soil.
Final Thoughts
Growing an onion from an onion is a fun, free way to get kitchen greens or run a small experiment, and separating the shoots carefully can get you a real handful of small bulbs. Just don’t plant your whole season’s storage crop this way — the biennial biology works against you. When you’re ready for a dependable harvest, start from sets or seed instead.
How This Guide Was Checked
Written by Ada Jones. The biennial growth pattern and realistic outcomes are checked against Grow Organic’s growing guide; the 21-bulb result is drawn from one grower’s own documented video, presented as a single example, not a verified average. Spot a mistake? Contact us and we’ll correct it.
Related Onion-Growing Guides
- Multiplier (Potato) Onions: How to Grow and Divide Them
- How to Regrow Green Onions in a Glass of Water
- Growing Onions From Seed: The Complete Step-by-Step Method
- Onion Sets vs Transplants vs Seeds: Which Should You Choose?
See the full How to Grow Onions guide for the complete seed-to-harvest walkthrough.
