More by gut instinct than science; when onions are planted close together as yours are, mine have seemed to stay green and grow but produce poor yield (bulb size).
I plant in late spring, and if for some reason plant some close together (lack of spce, too many plants) they stay green well into fall but I get what is more the size of ones thumb inspite of how long they were in the ground.
I would thin out some of your onions, use those as green onions.
I now, although I plant what I consider most important varieties well spaced, where they are more crowed, remove and eat as spring onions till spacing looks good.
Garlic, out side of some Elephant , actually not garlic, I planted two years ago, and were disappointing, are in a different world and I lost interest years back.
