This was the first significant change i made years ago,, compared to old bags of topsoil that most new guys use ( i have used this sh&$t). Promix bx is awesome but expensive @ 37$/ bale. Here ,, If your tight on cash you could find a landscape depot where they sell soil and bark & all that stuff and make your own "promix type soil" for a fraction of the price,,,,,, but if you can swing it ,,, by all means , promix with micorhizae is fool proof. ,