How to Regrow Spring Onions in Water (and What Really Happens)

Stand the white root ends in a little water and green shoots appear within days. It is a genuinely satisfying kitchen-scrap project — as long as you know what you do and do not get.

A bunch of spring onions costs very little, and the part most people throw away — the white base with the roots still attached — can be coaxed back into growth on a windowsill. It is one of the easiest kitchen-scrap projects there is. It is also one where the internet oversells the result, so let us be clear about what actually regrows.

What you get: fresh green tops you can snip for flavour, again and again for a while. What you do not get: a full, fat spring onion bulb the size of the one you bought. The white bases lengthen only slightly; the show is all in the leaves.

Step by step

Cut, don't pull. Use the green tops in cooking and keep the bottom 2–3 cm (about an inch) of the white base, with the roots left intact. A clean cut is fine; a ragged one still works.
Find a small glass. A narrow glass or jar holds the ends upright better than a wide bowl. A shot glass works well for a few onions at once.
Add a little water. Pour in just enough to cover the roots and the very bottom of the base — roughly 1 cm. Do not submerge the whole piece; the part above the water is what sprouts.
Stand them on a bright sill. A kitchen windowsill with good light is ideal. No light means pale, weak shoots; strong light means sturdier, greener ones.
Change the water every day or two. Stale water smells and encourages rot. Tip it out, rinse the roots and the glass, and refill. This one habit makes the difference between healthy green tops and a slimy mess.
Snip what you need. New green shoots appear within a few days and are ready to cut in one to two weeks. Cut them above the white base and the plant will usually send up more.

Roughly what to expect

In a warm kitchen the first green tips show in three to five days. By the end of the first week or two you have enough to snip. The plants keep producing for a while — often a few rounds of cutting — but the growth gets thinner each time as the stored energy in the base runs down.

Expect the project to fade after three or four cuttings, or sooner in low light. At that point the base has given what it had.

If you want more than green tops

Water alone cannot supply the nutrients a plant needs to build a proper bulb. If you want the onion to keep going, transfer the rooted base to a pot of compost once it has a few healthy shoots. Press it in so the white base sits just below the surface, keep it damp and give it light. In soil the plant can take up nutrients, so the shoots stay productive for longer and the base thickens.

Even in soil, though, these regrown onions rarely match a shop-bought one in size. Think of them as a supply of fresh green onion, not a replacement for buying bulbs.

When it goes wrong

Slimy, brown base. Too much water, or water left too long. Trim away the soft part and start again with fresh water daily.
Pale, floppy shoots. Not enough light. Move the glass to a brighter spot.
No growth after a week. The base was cut too short, or the roots were damaged. Leave at least 2 cm of white and keep the roots intact next time.

Why it works

A spring onion, like other alliums, stores energy in its base. When you keep that base and its roots alive, the plant can spend that stored energy on new leaves even with no soil. Water keeps the tissue from drying out and the roots functioning; light lets the new leaves photosynthesise. Once the stored energy is used up, growth depends on what the plant can draw from its surroundings — which is why soil gives a longer run than water alone.

Sources and research notes

Growth behaviour reflects general allium physiology; timings are typical home results in a warm kitchen and will vary with light and temperature.

RHS — growing onions

Written and edited by the Seedledge Editorial. Every guide answers one real growing question, is checked against the sources listed above, and is updated when guidance changes. We are an independent editorial desk, not horticultural professionals — read how we research and update our guides.