• Level 20 Tailoring.
  
• 'Horsy' the Pack Mule to bank materials.
  
• (Recommended) Scissors and Thimble for +5% exp boost each, both purchased from Tailoring trainer.

At level 20 Tailoring, you unlock the ability to harvest Northwind cotton. With the +10% exp boost from scissors and thimble, you get 83.8 exp per harvest averaging 2.5 yield per node.

There is an area northeast of Baronsgreene Village with Two clusters of Northwind cotton. Averaging around 60 total cotton that respawns after ~5 minutes. This method yields upwards of ~60k exp/hr.

The cotton picked is the primary ingredient used to craft Sorcery robes from lvl 20-35. This means you are also banking even more experience when you craft these robes later on if you choose to do so.