Organic wastes vary widely in pH without greatly affecting their suitability for composting. The optimum pH range for composting is somewhere in the range of 5.5 to 8.5. Odours from ammonia production are often a problem when the pH exceeds 9.

Apart from C and N, compost microorganisms need an adequate supply of other nutrients, such as phosphorus, sulphur, potassium and trace elements. These nutrients are usually present in ample concentrations in compost, though phosphorus (P) can sometimes be limiting. A C:P ratio of 75–150:1 is required.