The four main ingredients needed to compost are nitrogen, carbon, oxygen, and water. Nitrogen-rich materials include kitchen scraps (like vegetable peels and fruit rinds) and green grass clippings. Carbon sources include leaves, straw, sawdust, newspaper, cardboard, and wood chips. Oxygen is necessary for decomposition so it’s important to make sure your compost pile is aerated. Finally, water helps break down the materials and keep them from drying out; you want your compost to be as damp as a wrung-out sponge.