What You Can and Can't Compost
Every material here gets sorted by more than a yes or no — greens, browns, the "it depends" items, and the stuff to leave out, each with its carbon-to-nitrogen ratio and the actual reason behind the call.
Most "what can I compost" lists just sort things into yes and no, but that's not really how composting works. Nearly everything organic will decompose eventually; what matters is how it affects your pile's carbon-to-nitrogen balance, whether it draws in pests, and whether it's carrying seeds or pathogens your pile can actually kill. That's the logic this list is sorted by. The C:N figures come from the same feedstock database behind the C:N Ratio Calculator,[1][2] and they're representative ranges — real values move around with freshness, species, and moisture.
Greens — the nitrogen-rich materials
Greens are wet, fast-rotting, and nitrogen-rich (low C:N). They're what actually heats a pile up, but left on their own they mat down, go anaerobic, and start to smell. Balance them out 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 give the pile structure and air pockets, soak up extra moisture, and they're what most people never have enough of. Stockpile them when you can — dry autumn leaves will 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 all compostable — you just want to know the catch:
- Eggshells — compostable, and a solid source of calcium, but they don't so much break down as fragment. Their C:N is essentially all mineral. Crush them first so they spread through the pile instead of sitting whole.
- Bread, grains, and cooked starches — fine chemically (C:N ~50:1), but they'll pull in pests and can go moldy sitting on the surface. Bury them in the center of a hot pile.
- Citrus and onions — perfectly fine in a backyard pile, in moderation. Go easy on them in a worm bin though, since the acidity bothers the worms.
- Pine needles and oak leaves — acidic and waxy, so they break down slowly; use them as a minor ingredient, not the bulk of the pile. Once fully broken down, the finished compost isn't meaningfully acidic.
- Wood ash — a little adds potassium and limes the pile, but it's alkaline, so go light on it, and skip it altogether if your soil already leans alkaline.
- Weeds and diseased plants — safe only in a pile that holds 131°F (55°C) for three days, the benchmark for pathogen reduction;[12] the hotter end of that range also kills off most weed seeds. In a cold pile, they survive — keep them out unless you're composting hot; see the heating guide.
- "Compostable" plastics and PLA tableware — engineered to break down at industrial-composting temperatures, not in your backyard pile. Send them to municipal composting instead.
Keep these out of a home pile
A handful of materials just aren't worth the trouble 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 rules around meat, dairy, and pet waste really come down to two risks: pests and pathogens. A home pile rarely gets hot enough, for long enough, evenly enough, to guarantee it kills the pathogens in animal products and pet waste,[12] which is exactly why regulated composting facilities run on strict time-and-temperature rules. When you're not sure, 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 — fixing things when they go sideways, in the troubleshooting guide, and knowing how much compost to use once it's ready.
Frequently Asked Questions
Can you compost meat and dairy?
Not in a typical home pile. They're very high in nitrogen, break down slowly, throw off strong odors that draw rats and raccoons, and can carry 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 don't dump large amounts of citrus or onion in at once. Coffee grounds are a good nitrogen-rich green (~20:1). In a worm bin, add all three sparingly, since worms don't like acidity.
Can you compost paper and cardboard?
Yes. Plain newspaper, office paper, paper towels, brown bags, and corrugated cardboard are all excellent high-carbon browns — shred and moisten them so they don't mat down. Avoid glossy, waxed, or heavily colored paper.
Can you compost weeds and diseased plants?
Only in a hot pile. One that holds above 131°F (55°C) for three days reduces pathogens, and the hotter end of that range kills most weed seeds too. In a cold pile, both survive just fine, so keep seeding weeds and diseased plants out unless you're composting hot.
Can you compost pet waste?
Not in compost meant for vegetable gardens. Dog and cat waste can carry pathogens and parasites home composting doesn't reliably kill off. Keep it out of anything you'll put on food crops.