Ratio of carbon to nitrogen, typically in a compost heap.

C:N ratio or the Carbon:Nitrogen ratio (i.e. the ratio of carbon to nitrogen, by mass) is an important measure in composting. This ratio is an indicator of nitrogen limitation or over-supply.

Compost should ideally have a C:N ratio of about 20:1 to 30:1.

Add finely chopped woody material to increase the carbon content. Add leaves and composted manure to increase the nitrogen content.