Understanding the Carbon to Nitrogen Ratio (C:N)
Fungal-dominated composts begin with materials that have a higher carbon to nitrogen ratio, and bacterial-dominated composts contain materials with a lower C:N ratio. This ratio is sometimes referred to as the “brown to green ratio” because generally materials that are high in carbon are brown, woody, and/or dried and materials that are high in nitrogen are green and/or fresh. Therefore, fungal-dominated composts generally contain more brown materials, and bacterial-dominated composts generally contain more green materials.
Note: The most efficient decomposition occurs when the C:N ratio is between 25-30:1. Too much carbon (a high C:N ratio) causes decomposition to slow down and too much nitrogen (a low C:N ratio) can cause foul odors.
Common Sources of Carbon and Nitrogen in Compost
|Carbon-Containing Ingredients (Brown)||Nitrogen-Containing Ingredients (Green)|
|Dried Grass Clippings||Fresh Grass Clippings|
|Straw, Old Hay||Alfalfa, Fresh Hay|
|Wood Chips, Wood Ashes, Sawdust||Seaweed|
|Dried Leaves & Pine Needles||Kitchen Scraps, Coffee Grounds, Tea Bags|
|Black & White Newspaper||Blood Meal|
|Paper Towels, Tissue Paper||Manure|
|Shredded Cardboard||Garden Waste|
Materials to AVOID using in your compost pile include: large amounts of dried leaves and pine needles because they break down slowly and can affect pH levels, human and pet waste, waxed cardboard, colored newspaper, grease & oil, meat, dairy, weed seeds, and plastic.
Compost Mix Calculator – Determine the C:N ratio of up to four materials in a mix, from Klickitat County, Washington.
List of C:N Ratios for Compostable Materials – View this extensive list generated by the Oregon Biodynamics Group.