Help! Onions are forming offsets. Why?

I've never encountered this before, my onions have all formed offsets. Most have formed 3 and a couple 4. They are Sturon planted from sets and were started in my polytunnel in February.
They have been outside now for a while and are growing in a polystyrene fish box (can't grow them in the ground due to white rot).
I thought at first that maybe I'd been sold shallots in error but the leaves are much bigger than shallots and shallots form more offsets.

Anyone have any idea what may have caused this?

 

I dont think you have sturon Dave, surely they must be something different?

Your right they dont look like shallots either.

Will be interesting to see how they turn out.

 

It's really weird. They must be some form of onion I'm sure. They seemed to be growing normally until a few weeks ago and apart from the offsets they seem pretty healthy plants. Oh well looks like I'll not be stringing nice big onions this autumn!:(

 

From what I have read, in the Hessayon books, it could be down to planting at the wrong time, too much dry weather, or poor soil?

 

You may well be right regarding dry weather, we went away for a few days and the box they are growing in was pretty dry and they were starting to go a bit limp when we got back due to junior gardener forgetting to water them!

 

They look like tree onions to me, you'll soon know if they start forming bulbs where the flowers should be.

 

Yep, they look exactly like my tree onions (apparently also known as lazy onions as they grow to knee high then you can just pick them) which my neighbour gave me (although she said they were welsh onions which I think are similar ?)
As Ziggy says I guess you'll soon know if they form bulbs - they look nice and healthy though !

 

:tnp:Ahh, could be the weather, or a problem at the sett production stage then. Look forward to the outcome of this one.

 

interesting .... yeah some sort of shock/damage to the young growing tip may cause several new growing buds to form I suppose, or perhaps as you say a problem with set production.....