What You Can and Can't Compost
A master list of greens, browns, the "it depends" materials, and the things to keep out — each with its carbon-to-nitrogen ratio and the actual reason behind the rule, not just a yes or no.
Most "what can I compost" lists just sort things into yes and no. That's not quite how composting works. Nearly every organic material will decompose; the useful questions are how it affects your pile's carbon-to-nitrogen balance, whether it invites pests, and whether it carries seeds or pathogens your pile is hot enough to kill. This reference sorts materials by that logic. The C:N figures come from the same feedstock database behind the C:N Ratio Calculator,[1][2] and they're representative ranges — actual values shift with freshness, species, and moisture.
Greens — the nitrogen-rich materials
Greens are wet, fast-rotting, and nitrogen-rich (low C:N). They're the fuel that heats a pile, but on their own they mat down, go anaerobic, and smell. Balance them with browns.
| Material | Typical C:N | Notes |
|---|---|---|
| Vegetable scraps | ~15:1 | Ideal green; bury in the pile |
| Mixed food scraps | ~20:1 | Kitchen waste; keep out meat/dairy |
| Fruit waste & peels | ~28:1 | Citrus fine in moderation |
| Coffee grounds | ~20:1 | A "green" despite the brown color |
| Fresh grass clippings | 9–25:1 | Spread thin so they don't mat |
| Fresh green leaves & trimmings | ~25:1 | Garden prunings, deadheads |
| Green weeds (not seeding) | ~18:1 | Fine before they set seed |
| Herbivore manure (cow, horse, chicken, rabbit) | 6–30:1 | Age or hot-compost it first |
| Seaweed (fresh) | ~12:1 | Rinse off salt first |
Browns — the carbon-rich materials
Browns are dry, slow-rotting, and carbon-rich (high C:N). They provide structure and air spaces, absorb excess moisture, and are what most people are short on. Stockpile them — dry leaves in autumn keep for months.
| Material | Typical C:N | Notes |
|---|---|---|
| Dry autumn leaves | 40–80:1 | The home composter's workhorse brown |
| Straw (wheat, oat) | ~100:1 | Great structure; wets slowly |
| Cardboard (corrugated, plain) | 150–500:1 | Shred and wet so it doesn't mat |
| Newspaper & office paper | 150–200:1 | Plain, non-glossy only |
| Paper towels & brown bags | ~140:1 | Unbleached; no greasy paper |
| Wood chips (fresh / aged) | 150–400:1 | Slow; best for structure or mulch |
| Sawdust (untreated) | 200–750:1 | Very high carbon — use in thin layers |
| Corn stalks, woody stems | 50–100:1 | Chop for faster breakdown |
| Pine needles | 60–110:1 | Waxy and slow; use sparingly (see below) |
The "it depends" materials
These are compostable, but with a caveat worth knowing:
- Eggshells — compostable and a good source of calcium, but they don't really break down so much as fragment. Their C:N is essentially all mineral. Crush them first so they disperse.
- Bread, grains, and cooked starches — fine chemically (C:N ~50:1), but they attract pests and can go moldy on the surface. Bury them in the center of a hot pile.
- Citrus and onions — perfectly compostable in a backyard pile in moderation. Add sparingly to a worm bin, where the acidity bothers the worms.
- Pine needles and oak leaves — acidic and waxy, so they decompose slowly; use them as a minority component rather than the bulk of a pile. Their finished compost is not meaningfully acidic once broken down.
- Wood ash — small amounts add potassium and lime a pile, but it's alkaline, so go light and skip it entirely if your soil is already alkaline.
- Weeds and diseased plants — safe only in a pile that sustains 131°F (55°C) for three days, the benchmark for pathogen reduction;[12] the hotter upper end of that heat also kills most weed seeds. In a cold pile, keep them out — see the heating guide.
- "Compostable" plastics and PLA tableware — these are engineered to break down at industrial-composting temperatures, not in a backyard pile. Send them to municipal composting, not your heap.
Keep these out of a home pile
A few materials cause more trouble than they're worth in a backyard system:
| Keep out | Why |
|---|---|
| Meat, fish, bones | Slow, smelly, and a magnet for rats and raccoons; possible pathogens |
| Dairy, grease, oils, fatty food | Turn rancid, smell strongly, and attract pests |
| Dog and cat waste | Pathogens and parasites home piles don't reliably kill — never on food crops |
| Coal / charcoal-grill ash | Contains sulfur and heavy-metal residues harmful to plants |
| Treated, painted, or stained wood | Chemical preservatives and finishes leach into the compost |
| Glossy / coated / heavily inked paper | Coatings and some inks aren't things you want in soil |
| Persistent-herbicide-treated clippings or manure | Aminopyralid-type herbicides survive composting and damage garden plants |
The meat, dairy, and pet-waste rules are really about two risks: pests and pathogens. A home pile rarely runs hot enough, long enough, and evenly enough to guarantee it destroys the pathogens in animal products and pet waste,[12] which is exactly why regulated composting has strict time-and-temperature rules. When in doubt, leave it out.
Once you know what goes in, the next questions are getting the balance right — covered in how to start a compost pile — and fixing it when something's off, in the troubleshooting guide.
Frequently Asked Questions
Can you compost meat and dairy?
Not in a typical home pile. They're very high in nitrogen, break down slowly with strong odors that attract rats and raccoons, and can harbor pathogens a home pile may not kill. Keep them out of backyard and worm-bin composting.
Can you compost citrus, onions, and coffee grounds?
Yes to all three in a backyard pile — just avoid dumping large amounts of citrus or onion at once. Coffee grounds are a good nitrogen-rich green (~20:1). In a worm bin, add all three sparingly because worms dislike acidity.
Can you compost paper and cardboard?
Yes. Plain newspaper, office paper, paper towels, brown bags, and corrugated cardboard are excellent high-carbon browns — shred and moisten them so they don't mat. Avoid glossy, waxed, or heavily colored paper.
Can you compost weeds and diseased plants?
Only in a hot pile. A pile that sustains above 131°F (55°C) for three days reduces pathogens, and its hotter upper end kills most weed seeds. In a cold pile both survive, so keep seeding weeds and diseased plants out unless you compost hot.
Can you compost pet waste?
Not in compost for vegetable gardens. Dog and cat waste can carry pathogens and parasites home composting doesn't reliably destroy. Keep it out of any compost used on food crops.