Hasia is a herb that is used in mid level Alchemy and Cooking recipes. Hasia is more commonly used in Alchemy then Cooking. There are two great areas for players to farm for Hasia, one of these areas is right outside Beluslan Fortress and the other is in Salintinus Desert in Morheim. The area right outside Beluslan is easier to get to but will usually be much more crowded then the area in Morheim.
The reason the Beluslan area will be more crowded is for the obvious, it is right near a town. If you're looking for pure quanity of Hasia Morheim is your best bet. If you're looking to Extract this and other goodies for some cash Beluslan has Adamantium and Platinum nearby which will make you more money.