hmm, I will have to try to find ProMix at Home Depot.. haven't seen anything other than the MG mix,
but LanMan, you can use the MG potting soil mix if that is all you have, that is what I used for most of my plants so far that are in solo cups, I will have a new mix for when I put them into 1 gallon containers, mainly because MG is too expensive to try to get them in 2 cubic foot bags.. which they don't have anything larger than the normal bags around here, at least nothing large until summer.. but anyways, at the very least add a lot of Perlite.. the more the better for the most part, if you want to use vermiculite, just make sure it is the course kind, not fine, I found that if it is 'fine" it will just soak up the water and make the soil really dense and not drain at all.. so once i finish using up the vermiculite I have around, I will just stick to soil with a compost mixed in, and about 30-50% Perlite, just make sure if feels light and airy I guess when you mix the soil around.. I also suggest wetting it a tiny bit just enough to get it moist so that when you water it the first time it doesn't sink down like crazy.. but not so that it is wet, just damp.. so you can keep it really loose still
I am also going to try some of the Mykos stuff from RTI once I get it in the mail friday and see how that goes.. hopefully that and the compost will help break down the bone meal I had in the soil.. .oh and also shredded pine bark has been talked about a lot lately and is good for aeration and other things (I haven't read into it too much but got the idea from Baker's Peppers and there are a bunch of people talking about it lately on here.. so I am going to give it a shot when I put the 60 plants into 1 gallon containers sometime early next week)
bottom line, just make sure it is lite and drains well and there are some nutrients in there (which potting soil usually comes with slow release in there anyways) you can always add fertilizer later if they need it