Slowing down onion sets

[Bex2012]

2-3 weeks ago I put my onion sets in a 8" pot shoulder to shoulder, rather than leave them in the bag... Well they've gone a bit crazy! The roots are now poking out the bottom of the pots, and the green growth has got to be 6" tall on some of them. I probably wont be in a position to plant them out for a another few weeks, so is there any way of slowing them down? Or do I just leave them well alone?
They are currently in a mostly unheated conservatory. We might switch the heating on out there for a couple of hours in the evening.

[WendyC]

No doubt it's the warmth encouraging them to grow quickly so if you could put them somewhere cooler, but still in good light that might help. Could they go out during the day?

[Bex2012]

I actually stuck them out the garden this afternoon! The sun has finally moved round enough that its started to come back into the garden, so i stuck the onions, blueberry bushes and raspberry canes in the only patch of sunshine. I could put them in the shed i suppose, but i think we have mice in there.

[Paulieb]

They might have been better left dry for a little longer as they would have stayed dormant until they were planted out direct in March/April.

The main problem you'll have now/soon is that the roots will be really tangled when it comes to planting out and I think major root disturbance won't help with bolting issues later in the season.

Overwintering sets will sit in the coldall winter but I'm guessing spring planting sets aren't great with the cold. Do you know what variety they are?

I'd be tempted to stick them outside and leave them (at the risk of them succumbing to the cold) and/or trying to plant them in their final position asap. The cold will stop them growing for a month or so.

[Bex2012]

The reason i potted them up was because there were a few in the bag that looked a bit mouldy, and i didnt want it spread. They were only out of the poundshop, so its no big loss if i lose them (but woukd rather not if i can help it!).
I'll stick them in the shed tomorrow and see if that helps at all.

[Gillykat]

I've got mine in the greenhouse (in individual modules) but think it may be a touch too warm in there so would they be better being moved in to the polytunnel which is cooler as the lower sections aren't plastic but are windbreak material.