Yes you can use strictly gravel, although finer sized substrate like Pool Filter Sand can better anchor roots of certain plants ... then add gravel to the surface. With Sand and or gravel, it's best to dose ferts buy root tabs or liquid.
You could look to buy plant specific substrate like Eco-complete as it does provide nutrients that gravel doesn't ... however eventually those nutrients are used up so you'd have to add nutrients any way.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.