haha, no it wont be a good idea. the miracle gro needs a cap to hold it down. usually the cap is made of fine gravel or sand.
I did a npt a while back, it was great :) I now do eco complete /floramax and it's equally low maintainance. so it's really up to you.
I'm doung two types of low tech carpets (without CO2). one is a dwarf hair grass carpet, and the the one is with pearl weed, or as some call it baby tear (hermianthus glomeratus).
I've also previously done a microsword carpet as well.
whilst the above ones do much better in high light, dwarf saggitaria will do very well under low light...
the pearl weed is by far my favorite
(I have a very small tank, but imagine the possibilities in a large tank!)