The best results are going to come from using addatives/water feeding along with a good soil mix. See, your plant will have different stages in its life and will be able to use things at 5 weeks that it couldn't use at 2 weeks so if you know the plants life cycle you can feed it the appropriate nutes at the right time. You could mix a soil full of all kinds of goodies, but it would be like giving a baby a plate with baby food, hotdogs, steaks and corn on the cob, though all the foods are edable, not all of the foods are usable by the baby at that point.
Adieu