So, the question is actually if onions will bulb in late summer? I've always said no but only based on what other oldtimers have always told me. Now I see it first-hand due to my involvement with a large community garden complex. It was just today that one gardener asked why his red and white onions barely had 1" bulbs when a neighboring plot had the same onions almost twice as big. Barely 3 plots away, there are 3" yellow onions. In yet another plot, there are plants with only 2 leaves and a big flower stalk! The only difference is the planting date. We weren't able to get into the garden complex until about 15 May. Those who planted their onion sets immediately are going to get good bulbs. Those who delayed only 2 weeks are not going to get any large bulbs. Thus I had to inform my friend that his three 25' rows of onions may be best used as scallions. He accepted his lot and made a mental note to plant the onions first next year.

Martin

It may also matter if you started from seed or bulb,I think it will take another 3-4 weeks for them to bulb if they were started from seed and not starts or bulb sets.
Bill