I soloed 1-225 at level 12, here's how:
1-100 w/e starting area you are in
then you go to Hillsbrad, this is where you farm it all the way to 225.
South of southshore, head back and forth between the small islands (east-west) far out in the ocean, outside murloc/naga reach. Collect stranglekelp from 100 to 160.
Then you collect Liferoot from 160 ro 225. You go north, and head back and forth along the river to western plaguelands. All the liferoots are on the riverbanks. Your turning points should be the north part of chillwind camp to the north, and the waterfall to the south. Sometimes there is a node at the bottom part of the waterfall, so turn exactly at the waterfall.
Along the river there are turtles (non aggressive), and bears, spiders, lions (aggressive). None of the aggressive ones can swim, so whenever you aggro one just find some deep water and wait for him to unaggro.
The last points are quite painful (the whole liferoot grind took me approximately 4-6 hours).