[AlaninCarlisle]

I notice that once again some of the onions I planted as sets in March are starting to set seed. Any thoughts on how to prevent this in future please?

[mumofstig]

Perhaps buy heat-treated onion sets?
Most of the seed suppliers stock them for example
https://www.marshalls-seeds.co.uk/onion-sets-collection-heat-prepared-pid9727.html

[Nobbie]

Were they reds? I alway get this with reds and have given up growing them from sets. If whites, maybe they didn't like the very cold spell we had? I planted mine in modules in an unheated greenhouse and planted out at the end of April. Seem ok so far.

[Aidy]

I noticed this over the years and those who planted sets this year are having the same problem. I decided to try from seed this year and so far so good.
Everyone on our site who grow from seed seem to have the best results hence why I swapped.

[sunshineband]

It is my Autumn planted sets that are bolting. I have used heat treated sets this Spring and so far they are OK. The ones grown from seed are fine

PS Has anyone grown Autumn planted onions from seed?

[mumofstig]

I bought a packet of Kosma for Autumn sowing, now I have more space

VEGETABLE SEED - Onions - Kosma White Skinned Onion - Medwyns Prize Vegetable Seeds

[victoria park]

My Autumn planted ones have bolted quite a lot, maybe 50%, but a good crop nevertheless. They are rather large.
I suspect more and more onion sets are not treated in the way they should be, especially Autumn planted ones. I have been swapping to seeds for the last 3 years and have quite a few in the ground this year. Still learning about onion seeds, not the easiest to grow given their timings, but just about there now. The increased possibility of importing white rot on sets is another reason I have been swapping to seed.

[jaydig]

I found that onion sets, particularly the red varieties, tended to be prone to bolting, which is why I switched to growing from seed. I still get the occasional one that bolters, but not many.

[theothermarg]

Some of my overwintering onions have bolted and they were grown from seed !  They have hardly begun to swell either. I reckon it  might be the odd weather we are having

[Mr Dog]

Some of my overwintering onions have bolted and they were grown from seed !  They have hardly begun to swell either. I reckon it  might be the odd weather we are having

Onions are biennials so if we get 2 spells of cold over winter separated by warmth it can trick them into thinking that they're into their 2nd year, even if from seed. Sets are more easily tricked by smaller temperature swings.

[theothermarg]

Some of my overwintering onions have bolted and they were grown from seed !  They have hardly begun to swell either. I reckon it  might be the odd weather we are having

Onions are biennials so if we get 2 spells of cold over winter separated by warmth it can trick them into thinking that they're into their 2nd year, even if from seed. Sets are more easily tricked by smaller temperature swings.

Yes always thought sets bolted more. The onions that are left are finally swelling so might get some after all