Each time you harvest this, there's a small chance a Wind Flower will spawn in its place. It takes roughly 2 minutes for a new plant to spawn after harvesting the Wind Grass.
http://archeagedatabase.net/us/item/14778/

The best spot to find this is on the little cliff next to Gladosh the Butcher.
http://archeagedatabase.net/us/npc/7914/