Well damn just used a soil volume calculator, the box I made is 66 US gallons as it sits, so digging down 15” would make it equivalent to 132 gallon planters or just under 18 cu ft, but we need to add in an additional 9, native soil
Will be added back into the mix
So far I’m thinking
1/2 bale of promix (near 2 cu ft)
1 10lb bag worm castings (1/2 cu ft)
1 bag of good potting soil (probably coast of Maine potting mix peat / coco / forest moss etc) (2 cu ft)
An additional 10lb bag of perlite (1.5 cu ft? I’ll check my bag later)
1 bag composted manure (1 cu ft)
That’s around 7 cu ft of material,
Still considering more
Maybe additional peat moss? Might not even use promix, might use a cheaper one, we’ll see then maybe some more top soil?