Supercompost is a more potent version of compost and is used in conjunction with the Farming skill. Compost, supercompost, and ultracompost reduce the chance of a player’s crops becoming diseased whilst growing to rates of 1/4, 1/8, and 1/10 respectively, as well as increasing the minimum number of crops that will be received by the player upon harvest, even if those crops are protected.

One method to create supercompost is to place 15 suitable organic items (see list below) into any of the compost bins that are located next to the allotment patches found around RuneScape. Once the suitable items have been added, and the lid of the compost bin is closed, the contents will begin to rot, taking approximately 90 minutes until completion. During this time, the player may not open the compost bin or add any more items. Once the supercompost has finished rotting, the player may open the compost bin and extract all of the supercompost by using a bucket on it. 15 empty buckets are needed to empty all the supercompost from a compost bin. Each bucket of super compost collected by the player will grant that player 8.5 Farming experience. When used on a farming patch, each bucket will grant 26 Farming experience. Another method is to use one dose of compost potion on regular a regular compost. A player can also use one dose of compost potion on a filled compost bin containing regular compost, to turn all its content into supercompost.

As a rule of thumb, supercompost should only be used on farming patches that produce a valuable harvest (such as high-level herbs) and/or provide significant experience for each item harvested (such as watermelons). Supercompost cannot increase the yield of trees, fruit trees, or bush patches. Therefore, it is not recommended to treat those patches with supercompost if you plan to pay a gardener to watch over them, since there is no benefit other than the extra 26 experience granted.

Supercompost can also be purchased with reward points from the Tithe Farm minigame, costing 5 points per bucket.

The Lunar spell Fertile Soil can be used on a patch with the same effect as a supercompost. The spell can be upgraded to give the effect of ultracompost.

Players can add two volcanic ashes to a bucket of supercompost to upgrade it to ultracompost, or put 25 volcanic ash in a full compost bin that contains supercompost.