Illustration: Permaplans
C/N ratio
Carbon to nitrogen: the right mix decides whether compost rots, goes foul or just sits there.
Microorganisms need about 25–30 parts carbon (C) to 1 part nitrogen (N) while breaking things down. Carbon is their energy, nitrogen what they need to multiply.
| Material | C/N roughly |
|---|---|
| Urine, compost toilet matter | 6–10 |
| Fruit, vegetables, kitchen scraps | 15–20 |
| Grass clippings | 15–20 |
| Dry fruit, grain | 25 |
| Leaf litter | 40–60 |
| Straw | 80 |
| Wood chips | 100–500 |
- Too much nitrogen (below 20): the heap gets wet, smells of ammonia and goes foul.
- Too much carbon (above 35): little life, decay stalls.
- Good (20–35): warm, crumbly, smells of forest soil.
Rule of thumb: about two buckets of greens to one bucket of browns.
In Garden Survival a bar at the compost bin shows the ratio of the current batch. In the green band you get the full yield, outside it down to half the compost.