Icethorn is one of the high-end herbs of Wrath Classic, and it only spawns in the Storm Peaks, Icecrown and Wintergrasp. Most of the time, Lichbloom and Icethron share spawn points, and one of the two can spawn in the same location. Icethorn needs a Herbalism Skill of 435 to pick it. The herb is used in many high-end crafting recipes like Flask of the Frost Wyrm, Flask of Pure Mojo and Indestructible Potion.
Farming Icethorn in Storm Peaks
Many areas in the Storm Peaks are only reachable with a flying mount. In addition, many areas have high level monsters guarding the spawns. While challenging, this makes the zone great for herbalism farming, as many low-level players cannot farm here. Below is a map of the Icethorn spawns, though keep in mind that they share nodes with Lichbloom.
Icecrown Icethorn Farming
Icecrown has a few more spawn locations, that Storm Peaks. Though there might be some more competition from other people here, since Icecrown is also great for mining. This means that people with both mining and herbalism will go to Icecrown more often.