As an added precaution, we lined the bottom of our beds with cardboard, then added the soil and compost mix. It’s worked great in any of the beds we’re built through the years.
We always have cardboard from ‘Chewy’ orders and machine parts, etc. You can easily find cardboard in a grocery or liquor store dumpster if you don’t have any. Any business would probably be happy to give you all you need. :)
Put the cardboard on top of the grass? I’m not sure if I can get hubby to till it up, he’s kind of a whiner. He will only do his projects first.
Although part of the deal for him getting a big tractor is that he could dig holes for trees and he got a rototill attachment. Well, There’s no point having it if he’s not going to use it!