Some things decay faster than others. For example, kitchen waste, such as fruit and vegetable peelings, break down quickly. Cardboard pieces and tree branches rot very slowly. Waste products that are high-nitrogen include, fruit and vegetable peelings, seeds and grass clippings. Nitrogen-rich materials are usually green vegetation.
Animal waste is also high in nitrogen.
High-carbon materials are usually dry and tough plant parts, such as leaves, paper, tree branches and straw. The ideal balance for composting is 20 parts carbon to one part nitrogen. The two other necessary elements of composting are moisture and oxygen. The pile should be kept damp, but not wet. If the compost pile smells bad, it is probably too wet and it may not be getting enough oxygen.