If you want good soil, then make your own compost.
- 1x1x1 meter box. Fill it with garden waste, like leaves, flowers, roots, small branches, etc.
- Dig for, or buy earthworms online, and put them inside the box with all the other stuff.
- Stir it once in a while, so it don't rot.
Google more info on how to do it and what stuff to throw in there.