Sunshine :)

If beds were well prepared then really no need for any supplementary fertilisers.

However, some people use Nitrate of Soda as a top dressing round about now.
Then, mid July onwards you can use Chempak No 8 Low nitrogen/high potassium soluble fertliser to help with ripening, or straight sulphate of potash as a top dressing. depending on how they are bulbing up.

But as I say, I've never fertilised mine.

We've never fertilised ours either just made sure there was plenty of our home produced compost in the soil.

This is just a thought ... I think a feed high in nitrogen might help. Potassium is good for making things flower, and you don't want your onions to bolt.

Onions need a fair amount of potash to bulb up, though. Not much danger of them bolting until the bulb is fully formed.

Thanks every one for the help