I need a green thumb! Miracle-Gro, for one, makes a potting soil as well as a “garden soil”. Can they be used interchangeably? And if not, why not? Specifically, I am more concerned with using it as a garden soil. Also, is it safe on immature plants started from seeds being sown into a flowerbed? - Jinx
If you want to amend your garden soil to improve its water handling/nutritive/structural aspects, Miracle-Gro products are expensive and inefficient for the task. The ideal is a compost heap (leaves and other plant material break down into excellent stuff for improving soil).
Next best are commercially available composted manure/leaves/leafy material, then bulk soil from a reliable supplier.
The bagged garden soil/potting mixes differ somewhat in composition, but a lot of it is peat mixed with topsoil, forest scrapings, somewhat composted mulch and various other things including perlite and vermiculite (the stuff intended for containers should be lightweight with peat and perlite ingredients for good drainage).
Anything used to germinate seed indoors should be sterile. Outdoors, this isn’t too critical, but you do need a fine material without big lumps - and it should be easy to moisten and stay moist without getting soggy.