the easiest and cheapest way Ive found is go to where u plan to plant.overturn the native soil and break it up get rid of grass roots such.then take in ur premade soil mix and mix it in with the native soil.this is easier then digging holes and plants get used to native soil as well.raised bed work good as well if you make a square fill it with mix then roots can go into topsoil.If your usein promix mix in some soil like medium for water retention Do u want ? RECIPIE FOR SOIL?