Like always, I write about how I have been making gold, so on your realm they might sell for 1g instead. But these are time consuming to farm if you don't know where to do it, so it's often profitable to buy them and relist for a little bit more.
One Goldthorn node yields 1-8 Goldthorns. They do not respawn instantly so you often have to wait for more to spawn if you follow the routes found below. It's not a bad idea to pick every herb you run into so you don't have to stop and wait until more spawn. All herbs are valuable usually, except the lowest level flowers and some Cataclysm ones.
Stuff needed: 150 herbalism
Stuff recommended: Bountiful Bags guild perk
So where does one farm Goldthorn?
There are 3 places that are above other zones from my experience. If you don't like my suggestions, you can see where else it can be farmed by clicking here. Note that it can also be "skinned" from some monsters if you have herbalism, but it's often not worth the effort.
Addons used: Gathermate 2, Routes
Scarlet Monastery - Cathedral
There are 2 guaranteed Goldthorn spawn points within the instance. They are both near the fountain, one in the lower part of the instance and another one closer to the cathedral door.
It takes no more than a minute or two to grab them both and reset the instance. You can do this 5 times in a hour, so you quickly run into the instance cap. Still, this is the fastest way to farm these if you count how long it took to get a stack.
Once the limit is reached, you can have a pause or fly to Arathi Highlands which is not very far away. More goldthorn awaits there!
★ Check the Elite Gold Making page for the best gold making tricks ★
★ Use the automated gold making addon and make 30,000 gold a day ★
★ Read the Most Secret Gold Making Tricks that even I cannot mention! ★
★ Level alts & professions. 1-90 in 2½ days is the record with this addon ★