The major difference between topsoil and potting soil is that topsoil virtually never contains a soil lightener, whereas potting soil comes pre-mixed with perlite.

Kush referred to that stuff as being 'hot'- that means too high levels of nutrients.

I've grown successfully in a 50/50 mix of composted manure and perlite, that's it. I got some burn at first, but nothing outrageous.

The last time I mixed soil, I used a bag of topsoil a friend had left over from her lawn, a bag of composted manure, and a bag of perlite.

So to make any soil into potting soil, you need to add perlite or vermiculite.