Binding of Isaac: Rebirth Wiki

Added in Afterbirth †

Compost is an activated item added in The Binding of Isaac: Afterbirth †.


  • Upon use, converts pickups within the current room to Blue Flies or Blue Spiders.
  • Doubles Isaac's current amount of Blue Flies and Spiders.
    • If Isaac has no Blue Flies or Spiders, spawns one Blue Fly or Spider.


  • Does not work on Troll Bomb Troll Bombs or Mega Troll Bomb Mega Troll Bombs.
  • One character using it does not seem to double the spiders/flies for other characters. It only seems to double the ones following the character using the item.


  • Added in RepentanceBook of Virtues Book of Virtues: A wisp will only be summoned if Compost destroys at least one pickup, and the wisp's health will be equal to the number of pickups converted to Blue Flies/Spiders. If Isaac hits the blue fly cap of 64 as a result of using Compost, all but one of Isaac's wisps will despawn.
  • Car Battery Car Battery: Spawns 2 Blue Flies or Blue Spiders for each pickup removed, quadruples the current amount and spawns two if there is none.

In-game Footage[]


  • Compost is organic matter that has been decomposed and recycled as fertilizer.


Bug Bug! PC When using the item and obtaining an item (cards/pills/items) at the same time it will make the picked-up item disappear.