All organic matter is made up of a large amount of carbon (C) combined with smaller amounts of nitrogen (N). This balance in an organism is called the Carbon to Nitrogen ratio (C:N ratio). Compost scientists have determined that the fastest way to produce good quality compost is to maintain a C:N ratio somewhere around 25 to 30 parts carbon to 1 part nitrogen, or 25-30:1. If the C:N ratio is too high (too much carbon), the decomposition slows right down. If the C:N ratio is too low (too much nitrogen) you will end up with a very smelly compost pile.
In this table we have the average C:N ratios for the most commonly found organic materials. We consider high carbon content materials as "browns" and high nitrogen content as "greens".
Estimated Carbon to Nitrogen Ratios | |
Browns = High Carbon | C:N |
Ashes, wood | 25:1 |
Cardboard, shredded | 350:1 |
Corn stalks | 75:1 |
Fruit waste | 35:1 |
Leaves | 60:1 |
Newspaper, shredded | 175:1 |
Peanut shells | 35:1 |
Pine needles | 80:1 |
Sawdust | 325:1 |
Straw | 75:1 |
Wood chips | 400:1 |
Greens = High Nitrogen | C:N |
Alfalfa | 12:1 |
Clover | 23:1 |
Coffee grounds | 20:1 |
Food waste | 20:1 |
Garden waste | 30:1 |
Grass clippings | 20:1 |
Hay | 25:1 |
Manures | 15:1 |
Seaweed | 19:1 |
Vegetable scraps | 25:1 |
Weeds | 30:1 |