The 3 components in the soil ‘recipe’ are:
1/3 Blended Compost
This should include a minimum of 5 types of compost that you buy separately and mix together. Examples are aged cow manure, aged chicken manure, kelp meal, bat guano and worm castings. Perhaps you have your own compost you can also use.
1/3 Peat Moss
Coconut Coir fiber is an eco-friendly alternative to peat moss and can be substituted for the peat moss in this ‘recipe’.
1/3 Coarse Vermiculite
Mix equal parts of each, measured by volume, not by weight.
The 4'x4'x6" square foot garden box requires 8 cubic feet of soil mix made up of equal parts of the above 3 components.Try mixing the components on a large tarp in an area sheltered from wind as the ingredients are lightweight and blow easily until moistened. Wear a painter's mask and have a hose ready with a very fine spray. Do your math so you have sufficient amounts of each component ready. Roughly mix the three ingredients as best you can as you pour it on the tarp. By dragging two corners of the tarp to the opposite two corners, the material rolls over, mixing itself. It helps to have 2 people doing this. Keep repeating opposite corners until it's uniformly mixed and you don't see any single material or one color. Mist to wet down any dust, but don't spray so much you make puddles as the mixture will become too heavy to move easily. As you fill your square foot garden box, wet down the mixed-in layers as you fill it. Once the box is full and the top leveled off, don't pack it down. It will settle just right by itself. If you have any mix left over, bag it and set it aside for future use in pots or to top off the box when the soil level settles.