Greens vs Browns: The Compost Materials Table With C:N Values
Every compost guide tells you to balance "greens" and "browns." Greens are nitrogen-rich, moist materials; browns are carbon-rich, dry ones. What most guides skip is the actual number attached to each material — the carbon-to-nitrogen ratio — and the fact that those numbers are estimates that move around between labs and seasons. This table gives you both: a typical value and the published range behind it.
Key takeaways
- Greens (nitrogen) typically sit at 10–25:1; browns (carbon) range from 30:1 to over 500:1.
- Composting science targets a blend of roughly 25–30:1 at build time.
- Published C:N values are lab-variable estimates — the same cardboard measures ~107:1 in one Cornell dataset and up to 560:1 in another.
- By volume, Colorado State University Extension suggests about two parts green to one part brown as a starting mix.
- Weigh, don't scoop, when accuracy matters — run your mix through our C/N calculator.
Why the two groups exist
Compost microbes are built from roughly half carbon and need nitrogen for proteins and enzymes. Feed them nothing but nitrogen (a bin of pure grass clippings) and the excess escapes as smelly ammonia. Feed them almost pure carbon (a heap of dry straw) and the population stays small, cold and slow. The 25–30:1 blend keeps the microbes fed without waste — Cornell's Waste Management Institute calls about 30:1 the usual recommended starting range, and notes the finished compost settles near 10–15:1 as microbes exhale surplus carbon as CO₂. The full backstory is in the carbon-nitrogen ratio explained.
The greens: nitrogen-rich materials
| Green material | Typical C:N | Published range | Watch-outs |
|---|---|---|---|
| Grass clippings (fresh) | 19:1 | 12–25:1 | Wet; mats into airless layers |
| Fruit & vegetable scraps | 16:1 | 12–20:1 | Very wet; bury under browns |
| Coffee grounds (used) | 20:1 | 20:1 | Mild; most bins handle plenty |
| Cow manure | 20:1 | 20:1 | Hot-compost before food-garden use |
| Horse manure | 25:1 | ~25:1 (bedded: ~38:1) | Bedding counts as carbon |
| Poultry manure | 10:1 | 10:1 | Strong green; dose lightly |
| Poultry manure + litter | 16:1 | 13–18:1 | Shavings soften the punch |
Deeper detail on each one, including what "typical" hides: see the full greens list.
The browns: carbon-rich materials
| Brown material | Typical C:N | Published range | Watch-outs |
|---|---|---|---|
| Autumn leaves (dry) | 55:1 | 30–80:1 | The staple brown — stockpile them |
| Straw | 70:1 | 40–100:1 | Hollow stems add air |
| Corn stalks | 60:1 | 60:1 | Chop coarse stems |
| Bark / woody prunings | 115:1 | 100–130:1 | Slow; screen out later |
| Paper (shredded) | 175:1 | 150–200:1 | Skip glossy pages |
| Cardboard (shredded) | ~334:1 | 107–560:1 | Huge source disagreement; remove tape |
| Newspaper (shredded) | ~338:1 | 115–560:1 | Ditto — values vary wildly |
| Sawdust | 300:1 | 100–500:1 | Dense; thin layers only |
| Wood chips | 300:1 | 100–500:1 | Screen out before use |
| Peat moss | 38:1 | 38:1 | Mild brown; holds water |
Storage tactics (dry leaf hoards, cardboard pipelines) live in the full browns list and browns-shortage solutions.
Where these numbers come from
The table merges two families of sources. Colorado State University Extension's GardenNotes #246, Making Compost publishes the clean per-material ranges; the Cornell Waste Management Institute's Compost Chemistry and Raw Materials pages corroborate them and add lab-measured single values. Where the two disagree — cardboard and newspaper being the flamboyant cases — we show the whole span instead of pretending certainty. "Typical" is simply the midpoint of the published range, rounded.
Putting the table to work
A number is only useful if it changes what you do. Three moves cover most situations:
- Building a pile: layer alternating greens and browns, moisten as you go, then verify the blend in the C/N calculator — 2 kg of grass plus 3 kg of leaves, for instance, blends to about 40.6:1, which is still carbon-heavy and wants more greens.
- Correcting a live pile: ammonia smell = too green (add browns); slow and cool = too brown (add greens). The smelly-pile diagnostic flow walks through the wet-vs-green distinction.
- Replacing missing browns: CSU notes a browns-only pile can be rescued with about half a cup of nitrogen fertilizer per bushel — the same logic applies in reverse when greens run short in winter.