if you are just starting out with frogs and plants, then i HIGHLY recommend an ABG mix. you can make it yourself, or purchase it ready made. follow that up with a few inches of leaf litter, and you should have no problems whatsoever. i have used it in some of my emersed set ups, and it works perfectly fine. i don't even use regular aquarium gravel in my planted fish tanks. there are so many better, nutrient rich substrates out there. gravel is fine for a turtle tank, or a fish tank with plastic plants, but if you want real plants, you need to upgrade from that stuff.