Eeek!!! I left my onions far too long in the ground and they have grown HUGE!!! I must admit I did it as an experiment to see how large they would grow, however, it has meant I have lost a few due to rot. I have found the over-wintering varieties can rot from the base of the onion if they are left in the ground too long and I would normally harvest towards the end of June / early July depending on their size and whether the stalks have started to fall over.
This year the stalks have only recently started falling over, hence me leaving them in longer, but I think next year an early July harvest will be in order.
I have taken around 50% to deal with this week. I find if I take too many in one go it becomes a mammoth task to deal with them all. A little and often is a good motto as far as work on an allotment is concerned. Onions need drying out before my husband binds them into strings and hangs them for storage. I have placed mine in an old commercial bread basket – no idea where I got them from – raised on pots in the greenhouse.