Keep three to five centimetres of the white root end, stand it in a little water, and it regrows within a week. Move it into soil after the second harvest.
The water method
- Cut the onions about four centimetres above the roots, keeping the white base intact.
- Stand the bases upright in a glass with two centimetres of water, roots down.
- Put the glass on a bright windowsill.
- Change the water daily. This is the step people skip and it is why their second attempt smells.
- Harvest the green tops as needed, cutting rather than pulling.
You will see growth within two or three days. The first regrowth is usually as good as the original. The second is thinner. By the third, the plant has exhausted what was stored in the base and the flavour is noticeably weaker.
Why soil beats water after the first cycle
Water supplies no nutrients. The first regrowth runs on reserves in the white base, which is why it works so well and why it cannot continue indefinitely. Once those reserves are gone the plant needs feeding, and that means soil.
Pot the bases into ordinary compost with the white part buried and the join at soil level. From that point they behave like a normal crop and will produce for months, particularly if you keep cutting rather than letting them flower.
Getting more out of them
- Cut, do not pull. Pulling takes the growing point with it and ends that plant.
- Leave two centimetres of green. Cutting flush to the white slows regrowth considerably.
- Split clumps. Supermarket bunches often contain several plants held together. Separating them before potting gives each room to bulk up.
- Remove flower stalks. Once it bolts, the leaves toughen. Cutting the stalk out buys several more weeks.
The hygiene point
Regrowing in water on a kitchen counter is a warm, wet, nutrient-rich environment, which is exactly what bacteria like. Daily water changes and a rinse of the glass keep it fine. Slimy roots or a sour smell mean the batch has turned, and at that stage it belongs in the bin rather than on food.
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