Greens for Compost: The Complete List With C:N Values
Greens are the pile's nitrogen — fresh, moist, fast-rotting material that makes a heap heat up. They're also how piles go wrong: too many greens at once, especially wet ones, collapse into an airless, ammonia-scented mess. The list below pairs every common green with its typical C:N value and published range, drawing on Colorado State University Extension's GardenNotes #246 and Cornell Waste Management Institute tables.
Key takeaways
- Greens cluster at 10–25:1: grass clippings 12–25:1, veg scraps 12–20:1, coffee grounds 20:1.
- Manures are greens — poultry (10:1) is the strongest, always dose small.
- Wet greens are usually the cause of a stinking pile: drain, mix with bulky browns, restore air.
- Meat, bones, dairy and pet feces stay out of home piles (UMN Extension) — bokashi is the workaround.
- Weigh your greens — a "bucket of scraps" hides a lot of water weight.
The greens, ranked strong to mild
| Green | Typical C:N | Range | Best use & cautions |
|---|---|---|---|
| Poultry manure | 10:1 | 10:1 | Nitrogen bomb; thin layers, always with browns |
| Fruit & vegetable scraps | 16:1 | 12–20:1 | Chop small; bury under browns to deter flies |
| Poultry manure + litter | 16:1 | 13–18:1 | Litter's shavings soften the nitrogen hit |
| Coffee grounds (used) | 20:1 | 20:1 | Friendly green; filters count as a light brown |
| Cow manure | 20:1 | 20:1 | Classic activator; hot-compost before food gardens |
| Grass clippings (fresh) | 19:1 | 12–25:1 | Mix in — pure clumps mat and go anaerobic |
| Horse manure | 25:1 | ~25:1 (bedded ~38:1) | Bedding rides along as carbon |
| Fresh garden weeds | ~15–25:1 | varies | Seedless, non-diseased only; UMN lists weeds as acceptable |
(Weeds carry no single published value — moisture and species swing them — so they're shown as an approximate band rather than a sourced number. Treat them like other fresh, moist greens.)
Handling wet greens so they don't sabotage the pile
Most greens arrive loaded with water, and water is where trouble starts: Cornell's physics guidance puts optimum compost moisture at 50–60%, with odors and leaching beginning above about 65%. Kitchen fruit and vegetable scraps are often wetter than that on their own. Three habits keep a green-heavy addition safe:
- Balance at the moment of adding: for every tub of scraps, mix in shredded leaves, paper or cardboard immediately — verify amounts in the C/N calculator.
- Chop and scatter, don't dump: a whole bag of scraps in one corner becomes one anaerobic blob; UMN notes even grass clippings should be mixed with other waste so they don't mat and block oxygen.
- Bury near the hot core: the center of an active pile (130–160 °F, per UMN) decomposes scraps fastest and deters pests — bury fresh material in the interior rather than layering it on top.
Greens that are not welcome
- Meat, bones, grease, whole eggs, dairy: UMN Extension lists these as rodent magnets for home piles; they belong in bokashi (which handles even small bones) or municipal collection. See bokashi basics.
- Pet feces: disease risk; keep dog and cat waste out entirely.
- Diseased or heavily insect-infested plants, seedy weeds: a home pile may not heat enough to decontaminate them.
When greens run ahead of browns
Lawns outrun leaf supply: a mowing day can produce more green than the bin can safely absorb. Options: dry half the clippings in the sun for a day (they become a self-brown), feed thin layers into an active pile with plenty of browns, or hold scraps in a lidded bucket until brown material arrives. The strategy guide is browns-shortage solutions, and the failure mode to avoid is mapped in smelly-pile troubleshooting.
Ammonia is a nitrogen leak
A sharp ammonia smell means greens (nitrogen) exceed what microbes can use and the surplus is escaping as gas — lost fertilizer and a neighbor complaint. Fold in browns promptly; don't just re-turn a too-green, too-wet pile and expect the smell to leave.