HelpfulGardener.com

It's common to plant leek seedlings (with roots trimmed) in open holes and leave them like that for 'nature' to fill in. I wonder, is it OK to do that with onions? Do they need to have the little proto-bulb up at/near surface level or is it OK to let them settle as deep as they want into the planting hole?

my understanding is onions should only be “nestled” — about 1/3 of the bottom. But sometimes, when soil is not “fluffy”, the roots push them up and they fall over, requiring them to be “tucked” back in.