Grass is a source to work on your Living Stones. Make sure to merge level 1 Grass Tufts otherwise they will turn into Necromancer Grass. Level 2 to 4 Grass can be harvested for Fresh Stones. Level 5 to 8 can be harvested for Moss Covered Stones. 

The Grass Wonder is the Ensnared Virtue, Wonder #3 of the Dragon World.