I made this Deadnettle farming guide to help out players who want to farm the herbs instead of buying them from the Auction House. Deadnettle does not spawn in its own nodes, but instead is a random drop from picking other Northrend herbs, specifically Goldclover, Tiger Lily, and Talandra's Rose.
Grizzly Hills is the best place to farm Deadnettle because the zone is filled with Tiger Lily and Goldclover.
Howling Fjord is not much worse from Grizzly Hills, you get a tiny bit fewer herbs. Follow the yellow lines, only go to the red line if someone else is farming in the zone.