Compost Calculator

The Science of Rot: Mastering the C:N Ratio

Composting is biology, not magic. It is the process of aerobic bacteria breaking down organic matter. Like us, these bacteria need a balanced diet. Specifically, they need Carbon (C) for energy and Nitrogen (N) for protein synthesis. The ratio of these two elements determines whether your pile turns into rich "black gold" or a slimy, smelly mess.

The Magic Number: 30:1

The ideal Carbon-to-Nitrogen ratio for the fastest decomposition is roughly 30 parts Carbon to 1 part Nitrogen (30:1).
Too much Nitrogen (Low Ratio, e.g., 10:1): The bacteria cannot use all the nitrogen, so it is released as Ammonia gas. Result: A smelly, slimy pile that loses valuable nutrients.
Too much Carbon (High Ratio, e.g., 60:1): The bacteria run out of nitrogen (protein) and metabolism slows down. Result: A dry pile that sits there for years without changing.

Know Your Ingredients

The Greens (Nitrogen Sources)

• Grass Clippings: Very hot! C:N ~20:1. Use carefully; they can mat down and go anaerobic.
• Kitchen Scraps: Vegetable peels, coffee grounds, eggshells. C:N ~20:1.
• Manure (Cow/Horse): The classic activator. C:N ~15:1 to 25:1.
• Coffee Grounds: Surprisingly nitrogen-rich. C:N ~20:1.

The Browns (Carbon Sources)

• Dry Leaves: The staple of backyard composting. C:N ~60:1.
• Straw/Hay: Excellent structure builder. C:N ~75:1.
• Paper/Cardboard: Extremely high carbon. Shred it first. C:N ~170:1 to 350:1.
• Sawdust: Proceed with caution! Extremely high carbon. C:N ~300:1 to 500:1. A little goes a long way.

Troubleshooting Your Pile

Problem: Smells like rotten eggs.
Critique: Anaerobic condition (no air). Turn the pile and add coarse Browns (sticks, straw) to create air pockets.

Problem: Smells like ammonia.
Critique: Too much Nitrogen. Add carbon-rich materials like leaves or shredded paper immediately.

Problem: Pile is cold and nothing is happening.
Critique: Too much C, or too dry. Add water and Nitrogen (greens, manure, or even urine) to kickstart the heat.