Mot basic plants will be just fine for gravel. Very few plants are what are known as 'root-feeders' (taking their nutrients from the substrate). Things like grasses and baby tears are root-feeders. Most plants (anacharis, lacefern, rotala, ludwigia, all that) are water-column feeders. If you do want to add fertiliser, go with liquid ferts, such as Seachem Flourish. :) All my plants grow fine in gravel (and floating above the gravel where my cories dislodge them) with just a little bit of fertiliser. :)
You can get water lettuce for tanks, too. I believe OldFishLady has some in her STUNNING NPT. :)