Jeff Favelle November 4th, 2022
The Carbon To Nitrogen Ratio. What is it exactly? If you’ve ever read an article or watched a video on composting, sooner or later you will come across the term “Carbon To Nitrogen Ratio”.
Also called the C/N Ratio, the term refers to the relative ratio of Carbon (C) to Nitrogen (N) in either your total compost or the individual components that make it up. Individual parts of your compost have differing C/N rations (ie. green grass is about 10:1, while dry leaves are upwards of 60:1), and your compost as a whole has its own C/N ratio based on all these parts combined.
Ideally, we are aiming for a ratio of about 30:1 Carbon to Nitrogen, by weight. We achieve this desired ratio by mixing and matching the individual inputs of the compost as the season progresses. Its fluid and always-changing, dictated purely by what and how much we add.
But why is the ratio so important? Its important because of what each of these elements do for a compost. The ratio influences, more than any other aspect, your compost’s speed, efficiency, and success at breaking down the raw materials we add to it.
Carbon is the base building block of life and all organic matter, including that of your compost. Its also the energy source for the microbes that do all the work of breaking the compost down. They need Carbon for their cells and they need it at a ratio of 25 to 30 times greater than they need Nitrogen. Carbon sources, often referred to as “brown sources”, would be things such as dry leaves and twigs, wood chips, paper, cardboard, hay, and straw.
While Nitrogen is needed in far less amounts than Carbon, it is still vital to the whole process. Nitrogen is used to build proteins, amino acids, and the enzymes used for growth. Nitrogen tends to control the speed of the compost and often referred to as “hot”. Considered a “green” input, sources of Nitrogen include raw kitchen waste, green grass clippings, spent crops, fresh pulled weeds, manure, and even coffee grounds.
But what happens when the ratio isn’t observed? What happens when either Carbon or Nitrogen is in excess?
Well, bad things. Nothing that can’t be fixed, but a ratio that creeps too far away from the ideal range of 30:1 will start to underperform at best, and stop altogether at worst. Too high in Carbon and the compost will slow down. You pile will likely become too dry and left to persist, it will grind to a complete halt. Too little Carbon however, and the excess Nitrogen will also stall the process. In addition to that though, the Nitrogen will be released as ammonia gas and your compost will become a stinky, soggy mess.
It can always be reversed and nothing is ever permanent. Think of your compost as thus fluid, dynamic, interconnected web of biology that is constantly working for you and your garden.
Because it is!