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.