The box I cobbled together from old pallets, dirt is a mix of potting soil and local dirt spiced with chicken poo.
For the more observant viewers, you may notice that the closest 'V' is slimmer than the upper square -- the pallets were a little short. I plan to plant smaller vegetables in those areas.
But it's not like there are no alternatives to using pallet wood. You can't tell from looking what chemicals spilled on it. You can't know by asking a store clerk where a pallet was sourced from.
I didn't say don't garden (don't cross the street). I said don't garden with something that has a remote chance of being dangerous (look both ways).