To make a long story short, we had a massive weed in the backyard that required a fair amount of poisoning (non selective) before it could be removed. It turned out it was also the home to tens of thousands of ants, so they had to be poisoned too, using both ant powder and some pesticides sprayed by a professional. This was a couple months ago, and now we would like to turn that area into a veggie garden. We have had lots of rain but what can we do to make sure that the poisons are gone? Would laying some plastic sheeting and then fresh soil on top of that work? Or is that land just going to be permanently ruined?