How to Regrow Green Onions in Water: The Easiest Windowsill Food Project

If you’ve ever wondered whether you’re actually capable of growing any of your own food, this is the project that answers that question in under a week. You don’t need soil, a grow light, a balcony, or a single dollar you haven’t already spent — you need the root ends of green onions you were going to throw in the trash anyway. Put them in a glass of water on a sun-facing window and you’ll see new green growth within about five days. It’s the fastest, cheapest, lowest-risk way to find out that yes, you can grow something.

This article walks through exactly how to do it, how long it actually keeps producing (it isn’t forever, and you should know that going in), the mistakes that make people give up early, and a few other kitchen scraps worth trying once this one works.

What You Need

• Green onions (scallions) you’ve already bought for cooking — any bunch from the grocery store works.
• A small glass, jar, or cup. Anything that holds an inch or two of water and lets the roots sit in it.
• Water. Plain tap water is fine.
• A sun-facing window. Green onions aren’t fussy about light, but they’ll grow faster and sturdier with several hours of direct or bright indirect light a day.

That’s the entire list. No soil, no pot, no drainage tray, no equipment purchase of any kind.

Step-by-Step: How to Regrow Green Onions in Water

1. Save the root ends. Next time you use green onions in cooking, cut them about 5cm (2 inches) up from the white root base, where the white turns pale green. You want to keep the little cluster of roots at the bottom intact — that’s what regrows the plant. Use the green tops for cooking as normal.
2. Stand the roots in water. Place the root ends upright in a glass, with just the roots and the very bottom of the white part submerged — about 2–3cm (an inch) of water is enough. Don’t submerge the whole white stalk; sitting the cut top in water encourages rot rather than regrowth.
3. Set it in a sun-facing window. A spot that gets a few hours of light a day is enough. Green onions will grow in lower light too, just more slowly.
4. Change the water every 1–2 days. This is the step people skip, and it’s the one that matters most. Stagnant water grows bacteria and starts to smell; fresh water keeps the roots healthy and growing. Swap it out on a set schedule, like when you get up in the morning, so it isn’t left to your memory.
5. Watch for growth within 3–5 days. New green shoots appear from the center of the white base first. By day 5–7 you’ll typically have 5–8cm (2–3 inches) of new growth.
6. Harvest by snipping, not pulling. Once the new green tops reach a usable length — usually 10–15cm (4–6 inches), about a week or two in — snip what you need with scissors, leaving the white base and roots in the water. The plant keeps regrowing from that base for the next harvest.

How Many Harvests You’ll Actually Get

Here’s the part worth being straight about: this isn’t an infinite onion machine. One set of roots typically gives you 2 to 4 rounds of regrowth before the base is exhausted and stops producing usable new growth. Each round is a little slower and a little thinner than the last, since the root is drawing on stored energy rather than building new roots the way it would in soil.

That’s still real value — 2 to 4 free harvests from scraps you’d otherwise compost or bin — but it’s not a replacement for buying green onions long-term, and it’s worth knowing upfront so you’re not disappointed when growth slows in week three. When a base stops sending up new shoots, or the new growth comes in noticeably thin and pale, it’s done. Compost it and start a fresh set from your next bunch.

If you want a longer-running setup rather than repeating this cycle indefinitely, transplanting the rooted base into a small pot of soil after the first water-grown harvest extends its productive life further — the roots have something to keep building on instead of running down a fixed reserve.

Common Mistakes

• Submerging the whole stalk, not just the roots. Too much of the white part underwater invites rot instead of growth. Roots and the very base only.
• Letting the water go stale. Cloudy or smelly water means bacteria, not a failed plant — change it every 1–2 days without exception.
• Pulling the whole plant to harvest instead of snipping. Snipping the green tops leaves the base intact to regrow; pulling ends the cycle immediately.
• Expecting the roots to regrow forever. Two to four harvests is the realistic range. Treating a spent base as failed rather than finished leads people to think they did something wrong when they didn’t.
• Skipping the light entirely. Green onions will survive in a dim corner, but growth slows to a crawl. A sun-facing windowsill makes the difference between five days and two weeks.

Other Kitchen Scraps Worth Regrowing

Once green onions prove the concept, a few other common scraps work the same basic way — sitting a cut base in shallow water on a sun-facing windowsill:

• Romaine or leaf lettuce base: stand the root end in a shallow dish of water (just enough to cover the base, not submerge it) and new leaves sprout from the center within about a week. Good for a couple of small harvests before it’s spent.
• Celery: the same shallow-water method on the root end regrows a modest amount of new stalk over a few weeks — better for snipping into soups than for full stalks.
• Ginger: a piece of ginger root with at least one visible bud, left in water or planted directly into damp soil, will sprout new growth over several weeks — slower than the others, but useful if you cook with ginger often.

None of these are dramatic, and none replace buying fresh regularly — they’re small, free bonuses from food you already have, and a good way to keep testing what regrows and what doesn’t before committing time or money to anything bigger.

Where This Fits If You Want to Keep Going

Green onions in a cup of water is deliberately the smallest possible starting point — no equipment, no cost, no space commitment, which makes it worth trying even if you’re not sure you’ll stick with growing food at all. If it works for you (and for most people it does, within a week), it’s a reasonable signal that a slightly bigger step is worth trying next.

From here, growing lettuce indoors is the natural next step — same windowsill, similar light needs, but grown from seed rather than scraps, so it produces more and keeps going longer. If you’d rather stay in zero-equipment territory a bit longer, growing microgreens at home is another fast, cheap starting point that gives results in days rather than weeks. And once you’re ready to add a plant or two that doesn’t get eaten down to nothing, growing herbs indoors in an apartment is a good next layer.

If you’re renting and wondering whether any of this is realistic without a garden, a yard, or permission to modify anything, homesteading for renters and homesteading in an apartment both cover what’s actually achievable in a rented, no-land space — starting with exactly this kind of project.

For anyone who wants to keep a running list of small food wins like this one, our free starter guide is built around exactly this kind of low-commitment starting point — no pressure to build a full setup, just the next small thing worth trying.

Five days, one glass of water, and scraps you already had. That’s the whole barrier to entry.
Start with our free guide.