I have found lots of former postings regarding planting walking onions, but no one mentions how deep they are buried, or are they buried?

I just put mine in a week ago, but as I was doing it, I realized I didn't know how deep a trench I should dig or how much dirt to put over them. Or are they more laid on top of the soil than planted down in? I'm sure I can get some of the soil off them if I have them planted deeper than they should be.

Thanks. Carmellia