nah dragon resists grass so grass is neutral on garchomp, you just get the stab.
Interesting you said that... because I did a lets play of Pokémon Platnium... and while using Leafeon and her Leaf Blade it played the Super Effective sound.. Hrrm... maybe I wasn't paying attention.
Yep, Cressel you're right. Pardon my mistake.
"Defensively, Dragon types have resistances to Electric, Grass, Water and Fire. However, many fully-evolved Dragon-type Pokémon have a double weakness to Ice-type moves, due to their secondary types.Dragon is the only type resistant to all types of starter Pokémon, including Electric." -Bulbapedia