I have small Egyptian onions that were here when I bought the house and no matter how hard I try, I can't kill the darned things. Where they are is now a flower bed, but I swear if I put a house on them they would lift up the house and keep growing. I have dug them up with a shovel and they keep coming back. I can't use them because they grow over into the lawn as well, and my lawn service is not organic. Would not eat anything growing in the lawn. If your onions are anything like these, I would be more worried about putting a house on top of them. And it would the house I would be worried about, not the onions.
