You would either get a plant dragon or another moss dragon.
You get a plant dragon.
Cactus and Ash Dragons.
90% moss
The only thing you could get it is a tree dragon, because the only elements involved are earth and plant. Or, if you get SUPER lucky, you just MIGHT get a Rainbow Dragon.
A Plant dragon.
Plant Dragon and Cold Dragon
To date, there is no grass dragon in DragonVale. You may be thinking of the plant dragon. See the related question.
By Breeding Earth and Plant Dragon, you can also have Tropical Dragon with Earth and Plant.
You have to breed a plant and a fire dragon.
Plant and Cold
Metal & Plant
An evergreen (plant/cold), lichen (cold/plant), tree (plant/earth), moss (earth/plant), or mountain (cold/earth) could result from that combo.