Were they from seeds, from sets, when were they planted out?

Red onions from sets are prone to bolting. I only grow from seed and don't have a problem with bolting. Seeds were sown mid January, strong plants planted out end of April.

When I used to grow from sets many years ago, I started them off in cell trays in the greenhouse before planting out, as opposed to planting straight into open soil where the extremes of temperature fool the young sets into thinking summer is over, hence the production of seed heads. More chance that way of avoiding bolting.

they were planted as sets, il try seeds next year. thanks for that

At least they bolted. Mine mysteriously all went missing last year!!!!