Nan's Soil Mix
I am mixing one part from each bag. The first bag on the left is a "3/8" Minus" grade of crushed limestone for about $3.00. The center bag is generic bagged topsoil for about $2.50 The bag on the right is cow compost/manure
for about $3.00. The basic formula is one part of each. I use one bag of each, you can add a little more crushed limestone (the landscape rock has slightly less volume than the manure or topsoil per bag). I just mix one bag of each and throw in 4-6 cups of powdered limestone or dolomite rock per batch. Mix well and break up lumps with a shovel or trowel.
The correct limestone gravel can be a little hard to find, and is by far the best for this purpose. I checked at the national chain hardware stores and did not find what I thought was a small enough grade of rock, they have crushed limestone and crushed marble in like a 1 inch size, that's too large. I went to a landscape supplier and found the right stuff cheap
For more info on my soil mix and other
cultivation tips : Growing San Pedro