Onion sets or onion seeds? You do not say where you are in the UK... we planted onion sets a good month ago and would not expect to lift until late August, early September. Onion seed would be even later for us.

Hi Moon grower. These are onion sets they were planted out about 6 weeks ago. I am in West Yorkshire.

Probably mid to late August then... the neck should dry in on itself and the top start to die back. You can check by scraping the soil away carefully from he top of one of the bulbs.