Compost that breaks down slowly often lacks nitrogen, the most common limiting nutrient in the compost pile. Compost activators jump-start the composting process by providing a missing nutrient, usually nitrogen, needed by the microbes in the pile. Compost activators help break down materials high in carbon but low in nitrogen, like the large amounts of fallen leaves collected in the autumn. Compost activators should be layered alternately with the compost materials. In compost bins, compost accelerator should be mixed with the waste materials as the bin is filled.