Brown and Green Materials: The Basic Split
Compost works because it mixes two types of material: browns (carbon-rich) and greens (nitrogen-rich). Browns break down slowly and create air pockets. Greens break down fast and heat the pile. You need both, roughly three parts brown to one part green by volume, though the exact ratio is forgiving.
Browns include dry leaves, shredded paper, cardboard, straw, wood chips, and sawdust from untreated wood. Greens include grass clippings, vegetable scraps, coffee grounds, tea bags, and plant trimmings. A pile that smells like ammonia has too much green; a pile that does not heat up or break down has too much brown.
Key Takeaways
- Vegetables, fruit, coffee grounds, and grass clippings are safe greens; meat, dairy, oils, and diseased plants are not.
- Dry leaves, shredded paper, and untreated wood sawdust are safe browns; glossy paper, treated wood, and coal ash are not.
- Cooked food, pet waste, and diseased plant material attract pests or spread pathogens and should never go in.
- Citrus peels, onions, and garlic slow decomposition but are safe in small amounts mixed throughout the pile.
- Shred or chop large items before adding them so they break down faster and heat the pile more evenly.
Vegetables, Fruit, and Kitchen Scraps That Work
Raw vegetable and fruit scraps are ideal compost material. Carrot peels, apple cores, lettuce leaves, broccoli stems, banana peels, melon rinds, and potato skins all break down quickly and add nitrogen. Bury them under a layer of brown material so they do not attract flies or smell.
Coffee grounds and tea bags (remove the staple if there is one) are nitrogen-rich and welcome. Eggshells take longer to break down but add calcium and will eventually decompose. Crushed eggshells break down faster than whole ones.
Avoid cooked food, meat, fish, bones, dairy, oils, and fats. These attract rats, raccoons, and flies. They also create odor problems and can introduce pathogens. If you have a hot compost pile that reaches 140°F or higher and you turn it regularly, some sources say cooked vegetables are safe, but most home piles do not get hot enough, so the safer rule is to leave all cooked food out.
Garden and Yard Materials
Grass clippings, leaves, plant trimmings, and weeds are all safe if they come from plants that are not diseased. Diseased leaves or stems—those showing mold, spots, wilting, or unusual discoloration—should go in the trash or burned, not composted, because home piles often do not reach the temperature needed to kill pathogens.
Weeds are safe only if they have not gone to seed. If the weed has flowers or seed heads, leave it out or make sure your pile reaches 140°F and stays there for several days. Grass clippings from lawns treated with herbicide or pesticide should not go in if you plan to use the finished compost on a vegetable garden; clippings from untreated lawns are fine.
Wood chips and sawdust from untreated wood are excellent browns. Sawdust from pressure-treated lumber, plywood, or painted wood contains chemicals and should not be composted. Pine needles and conifer leaves are acidic and slow to break down but safe in small amounts; do not make them the bulk of your pile.
Paper, Cardboard, and Yard Waste
Shredded newspaper, plain cardboard (no tape or plastic windows), and kraft paper bags are all safe browns. Tear or shred them into pieces so they do not mat down and block air flow. Glossy paper, colored paper with heavy inks, and paper with plastic coating should not go in.
Straw and hay are safe if they are weed-free; hay often contains seeds, so straw is the safer choice. Wood ash from a wood stove or fireplace can go in, but only in small amounts—no more than 10 percent of the pile by volume—because it raises pH and can make the pile too alkaline. Coal ash should never be used.
What to Keep Out
Pet waste (dog or cat feces) should never be composted in a home pile because it can carry pathogens harmful to humans. Diseased plants, as mentioned, should be kept out. Invasive weeds like bindweed or Japanese knotweed should be burned or bagged for disposal, not composted, because even hot piles may not kill them completely.
Synthetic materials—plastic, rubber, metal, glass—do not belong in compost. Treated wood, plywood, and particle board contain glues and chemicals. Charcoal briquettes and coal ash are not safe. Glossy magazines, paper with heavy printing, and cardboard with plastic liners should be recycled or thrown away instead.
Citrus peels, onions, garlic, and hot peppers are technically safe but slow decomposition and can repel worms if you are vermicomposting. Use them sparingly, mixed throughout the pile rather than in clumps. Bread, pasta, and grains are safe but attract rodents, so bury them deep or leave them out if you have a pest problem.
How to Prepare Materials Before Adding Them
Chop or shred large items so they break down faster and heat the pile more evenly. Whole apple cores and large cardboard sheets take months; chopped apple pieces and shredded cardboard take weeks. A kitchen scrap chopper, food processor, or even a knife works for soft materials. A shredder handles leaves and paper quickly.
Wet materials like grass clippings should be spread out to dry slightly before adding, or mixed with brown material as you layer, so they do not compact into a soggy mat. Dry leaves can go in as-is but break down faster if shredded. Cardboard should be torn into pieces roughly 2 to 4 inches across.
Layering and Moisture Balance
Build your pile in layers: a few inches of brown, then a layer of green, then brown again. This creates air pockets and ensures the greens are surrounded by carbon-rich material, which speeds decomposition and reduces odor. Water each layer lightly as you go so the pile is as moist as a wrung-out sponge, not soggy.
If your pile smells like rotten eggs or ammonia, it is too wet or has too much green. Turn it and add more brown material. If it is not heating up or breaking down, it is too dry or has too much brown. Add water or more green material and turn it again.
Frequently Asked Questions
Can I put moldy food in compost?
Yes. Mold is part of decomposition, and moldy food breaks down faster than fresh food. Bury it under brown material so it does not attract flies.
What about nuts, seeds, and nut shells?
Nut shells take a very long time to break down—often a year or more—so they are not ideal for a home pile. Seeds and nuts themselves are safe but may sprout or attract rodents. Bury them deep or leave them out if pests are a problem.
Can I compost hair, nail clippings, or feathers?
Yes, all three are safe. They are high in nitrogen and will eventually decompose, though hair and feathers take longer than food scraps. Chop hair into short pieces so it does not mat.
Is it okay to put weeds with seeds in compost?
Only if your pile reaches and holds 140°F for several days, which most home piles do not. To be safe, remove seed heads before composting or throw seeded weeds in the trash.
Can I compost sawdust from my workshop?
Only if it is from untreated wood. Sawdust from pressure-treated lumber, plywood, MDF, or painted wood contains chemicals and should not be composted.