Compost Materials C:N Table
| Material | Type | C:N ratio | Handling note |
|---|---|---|---|
| Dry leaves | Brown | 40–80:1 | The backbone brown - shred to speed it up |
| Grass clippings | Green | 12–20:1 | Mats when wet - mix in, don't layer thick |
| Fruit & veg scraps | Green | 12–20:1 | Bury under a brown layer to hide the smell |
| Coffee grounds | Green | ~20:1 | Brown in colour, green in chemistry |
| Cardboard, shredded | Brown | ~350:1 | Wet it first or it sheds water in sheets |
| Sawdust | Brown | ~325:1 | Thin layers only - mats and locks out air |
| Straw | Brown | ~75:1 | Chopped lengths break down far faster |
| Pine needles | Brown | 60–110:1 | Waxy and slow - use sparingly |
| Corn stalks | Brown | ~60:1 | Chop first, they are woody |
| Horse manure | Green | ~25:1 | Nearly pile-ready on its own |
| Poultry manure | Green | ~10:1 | Nitrogen bomb - balance with heavy browns |
| Eggshells | Neutral | n/a | Minerals only, no effect on C:N |
A compost pile is a diet, and the carbon-to-nitrogen ratio is its macro balance: microbes building soil want roughly 25 to 30 parts carbon for every 1 part nitrogen by weight, and every ingredient on this chart is either a carbon-heavy brown or a nitrogen-heavy green. Pile up only browns - leaves, cardboard, sawdust - and the pile sits cold for a year, waiting for nitrogen that never arrives; pile up only greens - grass clippings, kitchen scraps - and it turns into a slimy, ammonia-smelling swamp before it ever becomes soil.
The ratios explain the recipes: dry leaves at 40-to-80-to-1 need about two shovel-fulls of greens per bag to land near 30:1, while grass clippings at 12-to-20-to-1 are already nitrogen-rich enough to be balanced by nothing more than the leaves they fell next to. That coincidence - autumn delivers the perfect brown exactly when the last mowing delivers the perfect green - is why fall is compost-making season and why the classic advice is to alternate layers of the two rather than weigh anything.
How to use
- Classify before you collect: browns are dry, woody or papery (leaves, cardboard, straw, sawdust, pine needles); greens are fresh, moist or nitrogen-rich (clippings, kitchen scraps, coffee grounds, manures). Colour is a trap - coffee grounds and fresh green leaves behave as greens regardless of appearance, because the nitrogen is in the chemistry, not the pigment.
- Aim the whole pile at 25-to-30-to-1, not each ingredient: mix roughly two to three parts browns by volume for every one part greens, adjust by what the pile does. Smells of ammonia means too much nitrogen - fold in cardboard or dry leaves. No heat after a week means too much carbon - add greens or water and turn.
- Check the table's notes before adding anything borderline: sawdust needs thin layers because it mats and locks air out; pine needles are slow even for a brown; eggshells add minerals without affecting C:N at all. Anything with oil, meat or dairy stays off the standard pile entirely - the chart covers the plant-and-manure side of the kitchen, not the grease.
Frequently asked questions
What is the ideal carbon to nitrogen ratio for compost?
About 25 to 30 parts carbon for every 1 part nitrogen by weight - the point where decomposer microbes run at full speed without starving for either nutrient. The chart's ingredient ratios are single-material numbers; the pile's ratio is the blend of everything in it, which is why the practical rule of thumb is two to three buckets of browns per bucket of greens, not lab arithmetic at the bin.
Are coffee grounds green or brown in compost?
Green, despite looking brown - spent coffee grounds run about 20 parts carbon to 1 part nitrogen, right in the greens band, and they heat a pile noticeably when added fresh. The common mistake is compensating for them as if they were leaves; treat them like grass clippings and balance with cardboard or dry leaves instead.
Why is my compost slimy and smelly?
Too much nitrogen with too little air - almost always a pile heavy on grass clippings or kitchen scraps that mats into airless layers. The fix is structural, not chemical: fold in a couple of armfuls of torn cardboard or dry leaves, turn the pile to reopen airflow, and bury future kitchen scraps under a brown layer so they are never exposed on the surface where the smell escapes.
Can I compost cardboard and paper?
Yes - shredded cardboard is one of the best browns at roughly 350-to-1, and plain paper runs similar, but both must be torn or shredded and moistened or they mat into dry sheets that shed water and air. Skip the waxed, plastic-coated and heavily-inked glossy stock; plain brown cardboard from boxes is the workhorse, and it is the fastest way to balance a pile that has just taken in a big batch of greens.
Which manure is best for compost?
Horse and poultry manures are the classic pair for opposite reasons: horse manure at about 25-to-1 is nearly pile-ready on its own, while poultry manure at about 10-to-1 is a nitrogen bomb that must be balanced heavily with browns or it turns ammonia-hot enough to burn plants. Cow manure sits between. Whatever the source, composting it first - not applying it raw - is what kills weed seeds and pathogens while keeping the nutrients.
How many leaves equal how much grass for good compost?
The autumn default works out near two bags of dry leaves per bag of fresh clippings: leaves at 40-to-80-to-1 average about 60, clippings near 15, and blending them roughly 2-to-1 by volume lands the pile near the 30:1 target once moisture is right. Exactness is unnecessary - the pile self-corrects if you watch its signals, heat and smell, and adjust the next layer rather than digging everything back out.