Mulch is created at a 40% rate when processing an Apple into Apple Juice in a Squeezer. Another way to get Mulch is to use the Moistener. It will process Wheat to Mouldy Wheat to Decaying Wheat and then into Mulch.
It is used for either making Humus or Bog Earth in a Carpenter . It can also be used as a catalyst in a Fermenter to create Biomass.