Composter allows you to compost leaves, needles, saplings, grass and some other items.
Composting speed depends on composter fill and C:N ratio. Composter should be placed on soil, to work faster.
You can craft garden soil from dirt and compost lumps. Some plants (from mod farming, Farming Redo and hades_extrafarming) grows faster on garden soil.
See settingtypes.txt for check configuration posibilities.