The Composter in Minecraft is a block that will convert crops, plants, and other compostable materials into bone meal. This is great, as anyone with a decent farm in Minecraft will attest to how much bone meal you will need to help fertilize your plants. Composters allow you to rapidly get rid of excess plant material, including poisonous potatoes, and turn it into something that will be very useful.
How To Make A Composter
To make a Composter, you will need to place seven of any type of wooden slabs in a U shape on your Crafting Table, leaving the top and middle squares open. You can make wooden slabs by placing three wooden planks in the Crafting Table, along the bottom row. Composters can also spawn in all villages.
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The Composter is used to created Bone Meal by merely adding the plant materials to the composter. By adding an item to the composter, you have a chance to add a layer of compost. Various items in the game have a different change of adding compost. For a full list of the items, and their chance of adding compost, I would suggest checking out the Minecraft Gamepedia.
Once you have collected seven layers of compost in the Composter, you can then use it a final time to collect the Bone Meal. You can also use Composters in conjunction with Hoppers to have the Hopper automatically collect the Bone Meal. To do this, place the composter on the upper side of the Hopper.