Source: wikihow

A guide to make RS gold by collecting Limpwurt Root

Limpwurt roots can be dropped by many monsters and also you can buy them at Poletax’s Herblore Shop using RS gold. Players can also grow their own Limpwurt root as long as their Farming skill is level 26 using Limpwurt seeds. These roots can be used to make super strength potion and strength potion combined with Kwuarm.

Before collecting Limpwurt roots, the players must need level 20 Dungeoneering, level 25 Magic skills, and a brass key. You can buy brass key at the Grand Exchange as long as you have enough Rs gold in your pocket.

You can get Limpwurt roots by climbing down the ladder from the little house from the west of entrance of Grand Exchange. Once down, head south and go through the dungeon entrance. You will find Limpwurt roots inside the small dungeon. They spawn every 30 seconds, so collect all until your inventory is full. Once your inventory is full, sell them all in Grand exchange for RS gold.