I’ve been regrowing shop-bought spring onions / salad onions for about 10 years. If you buy a pack that has those spindly little white roots still attached (most of them have them) you can place them in water and regrow them.
It occurred to me today that at this particular time, this can be done very easily even if you are self-isolating, to make your spring onions go further. Kids would probably love to do it. Best of all, after you cut your first crop, they will grow back! You should get several crops in a single season. They will be dormant in winter but will come back in spring.
Note that these will not grow into the same solid spring onion that you originally purchased, but they will produce giant, hollow chives, which are utterly delicious in salads, mashed into spud, or fine-chopped and sprinkled over stews and casseroles. You can see mine in the photo to the left. I first planted them last year and they are still going strong in their pot this year.
I don’t actually have any shop-bought spring onions at the moment, or I would photograph the process, but it’s dead simple and here’s how I’ve been doing it for years:
Buy spring onions that have their little white hair-like roots still attached, such as the ones in the picture on the right (which I’ve borrowed from the Ocado website). If they have been cut off, this won’t work.
As soon as you have your spring onions home, cut off the last 3-4cm (a bit over an inch) that have the roots still attached. Place these in glass or jar of cold water (a glass or jar is better than a cup so that you can watch what’s happening). You only need enough water to cover the roots and a bit of the stem.
In a couple of days new, healthy white roots will appear and start growing. When the new roots reach a good size (I find that anything over 3-4cms / an inch long works) you can plant them out into your garden or into pots (or the bottoms of used plastic bottles, with holes made in the bottom for drainage).
When you plant them, make sure that whilst the roots are under the surface, a bit of green remains, sticking up. Water well, and keep moist, but don’t drown. In only a couple of weeks they will begin to grow and when they reach a good height you can cut them and eat them. Best of all, they will regrow! The photograph at the top of the page shows the ones I planted last year and am still eating today (quite literally – they are going to be sprinkled over tonight’s home-made curry to give it a bit of zing in the absence of any coriander).