Compost potions (also known as supercompost potions) are used to make supercompost. Players may use a dose on compost to make it into supercompost, or use a dose on a full compost bin to obtain 15 supercomposts.
Players are advised to use these potions for their own compost bins instead of selling them away, as they will earn more by making buckets of supercompost. Note that the player cannot add a dose of compost potion to compost bins containing a combination of normal compost and supercompost vegetation (in any combination).
A player using a compost potion, making all the Compost in the bin Supercompost.
This potion cannot be made with the Herbloreskill. Because of this, the item almost never is purchasable on the Grand Exchange in any number of doses, as they are never readily available, and people make more money by making supercompost without them. It is much simpler and cheaper to simply use pineapples on the compost bin than using these potions. These can be grown by the player, or picked from the plants around the Karamja Lodestone (hopping worlds to gather more quickly does work).
This potion is one of the few un-drinkable potions in the game. This may explain why it cannot be made using Herblore.