I used to work for Stan Thonson and he always made his own. Will phone them and he will give me his recipe.

The thing about potting soil is it's not soil. It's usually peat moss based, with some vermiculite &/or perlite mixed in to keep it from caking, and a bit of fertilizer. You can buy all these things separately but it doesn't save any money. Some potting soils contain municipal compost, which you can also make yourself.

For me the most economical way for potting lots of plants is to buy a big cube/bale of Pro Mix. It's good for seedlings and adult plants alike, and is better quality than most bagged soils.

I vote for Pro Mix also. Problem is, I have to go out of town to get it, so always pick up a bale if I'm in Wpg. whether I need it at the time or not.