Sounds from post #1 like there may be a confusion over terms. Substrate is the material on the floor of the tank, be it sand, gravel, dirt, mixes of peat, etc. The plants grow in the substrate, and a host of important bacteria colonize it.
To grow plants you do not need any special substrate. Particle size can make a difference, if it is too large. But otherwise, almost any substrate will work.
I have used various gravels over the years, and sand, and an enriched substrate (one specially made for plants). The latter was not worth the money in my view. Sand works fine, I use play sand as it replicates the sand in Amazon streams. I have fine gravel in one tank, but the rest are now play sand.