They can be obtained as drops from monsters (or reward chests/minigames), or farmed using the Farming skill.
An easy way to store large amounts of (grimy) herbs (while on a Slayer task or farming), especially as an Ultimate Ironman, is by using the Herbsack obtainable through the Skill points shop.
Before they can be used in the Herblore skill, the Grimy toadflax needs to be cleaned, which requires a herblore level of 30 and earning the player 400 Herblore experience (or 80 if they are playing an Extremegamemode, excluding any experience boosts)
The player may also choose to let the Herbalist clean all of their herbs for them for a small, this will not require a herblore level but also will not provide any experience, however it will instantly clean any amount of (noted) herbs you may have.
^"Last average price". RuneRealm. "This price is a weighted average based on actual purchases on the in-game auction, however the wiki's prices only get updated from in-game changes every few days."
Herblore
