Rather than thinking in terms of strict “can” and “can’t” lists, it is often more helpful to think about composting as a diet for decomposer microbes. Different materials break down at very different rates and place different demands on air, moisture, and structure.
Easy or soft materials are rich in sugars, starches, and other readily available compounds. These include vegetable peelings, soft green waste, and fresh grass. They break down quickly but can cause problems if added in large amounts without structure.
Medium materials are dominated by plant fibres such as cellulose. Leaves, stems, and mixed garden trimmings sit in this category. They decompose steadily and form the bulk of most domestic compost heaps.
Hard or woody materials contain tougher fibres and lignin that only a smaller group of specialist microbes can break down. Twigs, wood chips, and woody prunings decompose slowly and tend to control the overall time horizon of the composting mass.
Most composting problems arise when one group dominates the mix, rather than from the presence of any single material.
Tip to improve: Aim for a mixed ‘diet’. Balance easy, fast‑rotting materials with enough fibrous and woody material to maintain air spaces and keep the composting process stable over time.
