Composting
What is the C:N Ratio and Why is it Important?
The carbon to nitrogen ratio (C:N ratio) is the relative percentage of
carbon to that of nitrogen in various organic materials. Decomposing
microbes are the most active and efficient when the C:N ratio is 30:1.
The more carbon in the pile relative to nitrogen, the longer the
decomposition process. Excess nitrogen causes the pile to lose nitrogen
to the atmosphere as ammonia gas.
Carbon materials are usually dry and brown (examples: straw, paper,
fall leaves, & hay)
Nitrogen materials are usually green and wet (examples: grass
clippings, freshly pulled plants, fruit & vegetable kitchen scraps, and
coffee grounds.) When no nitrogen materials are available, fertilizer
can be used to provide the nitrogen if desired. Apply one cup of
fertilizer, such as 13-13-13, for every 10 square feet of pile surface
area. This could be applied again each time you add another 6 inches of
high carbon material.
A rule of thumb on C:N ratio is about ¼ - ½ of the pile volume nitrogen
materials and ½ - ¾ carbon materials.
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