Growing your own onion sets

[ameno]

Has anyone ever tried growing their own onion sets from seed, to be planted the following year?
I ask because I sort of accidentally grew some myself last year, when I forgot about a seed tray of spring onion seedlings (Lilia, which is a dual purpose variety which can also be left to grow full sized onions), and because of the cramped conditions they formed small bulbs and then went dormant, and then start growing again over the winter.
I planted these small onion plants out bare root in March, and the ones which haven't been eaten by slugs seem to be doing pretty well, so I'm wondering if I could do it on a large scale this year.
Growing onions from seed the normal way just isn't practical for me. They take up far too much space indoors and need far too much compost. A couple of seed trays filled with very closely spaced seedlings grown outdoors over the previous summer, though, would be no problem.

[Snoop Puss]

That's interesting, ameno. I've never done that, no. But I'm interested to hear how they do. My instinctive expectation is that they'll bolt. But by the sound of it, you've got a good variety for trying. And somebody has to grow sets somehow.

Will you keep us updated? I'm going to subscribe to this thread to keep track of other comments and your progress.

[ameno]

I'll try to keep you updated, yeah.
In theory, they shouldn't bolt. Something like this is how they grow onion sets in the first place: onions are grown from seed at very close spacing, and thus they go dormant whilst still too small to flower, and then instead of flowering the next year they just continue growing.

[Snoop Puss]

Sounds like you have your own answer, ameno.

Will follow with interest.

The closest I come to anything like this is growing calçots, but even then they're very different. A full-sized onion is grown and then lifted. It's kept out of the ground for a couple of months or more before being replanted any time from August onwards. What's eaten early or very late winter (depending on when the onion is put back in the ground) is the shoots that sprout up from the onion, which rots away.

[Mark Rand]

Don't forget that onion sets are often heat treated to reduce bolting.

[hamesy]

Onion sets are normally heat treated to stop bolting.

I planted some onions in a spare patch of ground down the allotment a few years ago and for some reason I forgot to harvest one of them. The following year, it started to grow but didn't bolt. I left it in the ground to see what would happen and since then, it's grown each year and last year was the first time it bolted. It's still in the ground and started to put on new growth.

[starloc]

I grow standard onions as spring onions, i left a few of them 3 years ago, the next year they all grew 2 inch wide onion each, i again didnt harvest them and then last year I got a bunch of onions forming from side growths on the bulbs 3 or so on each onion ,the center oldest one flowered and then shriveled after flowering, the extra side onions were big onions so i harvested them when they were ready.
Onion sets you buy, only some are heat treated, either the ones for winter planting or spring planting