Originally posted by Luward:

@DeMasked I have found seeds in chests that are in stone ruins with draugr or skeletons and also in a ruined cabin with skeletons. All in mountains. I found one stone ruin that had draugr but the chest didn't have onion seeds.

Good to know. I found 2 stone towers with nothing and then some random stone platform jutting from the side of a cliff that was kinda odd - maybe a place to build on or throw up a bonfire.