Seedlings need clean, unfertilized soil. You're stuck buying that- promix, seedling starting mix, sunshine mix, etc. are fine.
For older plants, you can be more creative. Look in the [organic' section and see what organic growers are using for a mix. If you grow indoors, bagged compost is better than backyard compost because of the risk of bugs and weed seeds. I grow in a compost + perlite mix and like it a lot. Blood, bone, and fish meal are good but you need to look up how much to use so you don't hurt the plants.