Browns and Greens: The Two Categories That Matter

Compostable material falls into two groups: browns (carbon-rich) and greens (nitrogen-rich). Browns are dry: leaves, shredded paper, cardboard, straw, wood chips. Greens are wet or fresh: grass clippings, vegetable scraps, coffee grounds, plant trimmings. A working pile needs both. Too many browns and decomposition slows; too many greens and the pile becomes a wet, smelly mess.

The ratio matters less than people think. Aim for roughly three parts brown to one part green by volume, but a pile that leans slightly one way will still break down—it just takes longer. The key is that you have some of each, layered or mixed together.

Key Takeaways

  • Vegetable and fruit scraps, coffee grounds, eggshells, and grass clippings are safe to compost and break down quickly.
  • Meat, fish, dairy, oils, and diseased plants should never go in a home compost pile because they attract pests or spread disease.
  • Cardboard, newspaper, leaves, and wood chips are excellent browns that balance the moisture in your pile.
  • Coated or glossy paper, treated wood, and pet waste will not break down properly and can contaminate finished compost.

Vegetable and Fruit Scraps You Should Compost

Nearly all vegetable and fruit scraps belong in the pile: carrot peels, apple cores, banana peels, lettuce leaves, broccoli stems, onion skins, potato peels, melon rinds. Citrus peels take longer to break down but will decompose. Avocado pits and shells also compost, though slowly. These are greens—they add nitrogen and moisture, and they break down within weeks to a few months depending on pile temperature and how finely you chop them.

Chop larger pieces into smaller chunks. A whole apple takes months; apple pieces take weeks. The smaller the surface area, the faster microbes can work. This is not required, but it speeds the process significantly.

What Never Goes in Home Compost

Meat, fish, bones, and seafood shells should never enter a home pile. They decompose very slowly, smell strongly during breakdown, and attract rats, raccoons, and flies. Commercial composting facilities reach high enough temperatures to kill pathogens and break down these materials safely; home piles do not.

Dairy products—milk, cheese, yogurt, butter—also attract pests and create odor problems. Oils and fats (cooking oil, grease, salad dressing) slow decomposition and can waterproof the pile, preventing air and moisture from moving through it. Pet waste (dog or cat feces) contains pathogens harmful to humans and should never be composted at home, even in a separate pile.

Diseased plants and weeds with seeds belong in the trash or yard waste bin, not your pile. Home compost rarely reaches the temperature needed to kill plant diseases or weed seeds. Composting them spreads the problem to your garden.

Paper, Cardboard, and Wood You Can Use

Newspaper, cardboard boxes, paper bags, and shredded office paper all compost. Remove tape, plastic windows, and stickers first. Cardboard breaks down faster if you tear or shred it. Wet cardboard before adding it so it does not blow away and so it absorbs moisture from the pile.

Wood chips, sawdust, and untreated wood scraps are excellent browns. Avoid pressure-treated wood, which contains arsenic and other chemicals that persist in finished compost. Plywood and particle board contain glues that do not break down. Plain wood—branches, logs, untreated lumber—is safe.

Glossy or coated paper (magazines, catalogs, takeout containers with plastic lining) should not go in. The coating does not compost and can contain chemicals. Wax-coated cardboard (milk cartons, juice boxes) is borderline; it will eventually break down, but the wax coating lingers for years.

Yard Waste and Garden Material

Grass clippings, leaves, plant trimmings, and flower stems all compost. Leaves are an excellent brown when dry; grass clippings are a green. If you have a large pile of fresh grass clippings, mix them with brown material or spread them out to dry first—a dense mat of wet grass can become anaerobic (oxygen-starved) and smell like ammonia.

Hay and straw compost, but straw is preferable because hay contains weed seeds. Pine needles and conifer needles take years to break down and make the pile acidic; use them sparingly or skip them. Sawdust from untreated wood is fine; sawdust from treated or painted wood is not.

Coffee, Tea, and Kitchen Odds and Ends

Coffee grounds and paper filters compost quickly. Tea bags compost too, but remove the staple first if there is one. Eggshells break down slowly but add calcium; crush them to speed the process. Nut shells (walnut, almond, peanut) compost but take a long time.

Bread, pasta, rice, and cooked grains can go in, but they attract pests more readily than raw vegetables. If you add them, bury them deep in the pile under brown material. Peanut butter and other nut butters are high in oil and should be avoided. Moldy food is fine—mold is part of decomposition.

What Slows Down or Contaminates Your Pile

Glossy or colored paper, treated wood, synthetic materials, and plastics do not belong in compost. Dryer lint contains synthetic fibers and should not go in. Charcoal ash (from a grill) contains chemicals; wood ash from a fireplace is acceptable in small amounts but can make the pile too alkaline if overused.

Sawdust from sanded or stained wood, wood treated with preservatives, and plywood all contain substances that persist in finished compost and can harm plants or soil. If you are unsure whether wood has been treated, leave it out.

Frequently Asked Questions

Can I compost onions and garlic?

Yes. Onion skins, garlic skins, and garlic cloves all compost. Some people worry they will repel worms, but they break down fine in a standard pile. If you are using a worm bin, add them in moderation since worms dislike strong-smelling materials.

What about bread and pasta?

Both compost, but they attract rodents and insects faster than vegetable scraps. Bury them under at least six inches of brown material (leaves, cardboard, wood chips) so they are not visible on the surface. This slows pest attraction significantly.

Can I compost pine needles and conifer branches?

They will eventually compost, but very slowly—often two to three years. They also acidify the pile. If you have a small amount, mix them in; if you have large quantities, consider yard waste pickup instead.

Is it safe to compost diseased plant material?

No. Home compost piles do not reach the temperature needed to kill plant pathogens. Composting diseased plants spreads the disease to your garden when you use the finished compost. Put diseased material in the trash or yard waste bin.

Can I compost paper with ink on it?

Yes. Newspaper and printed office paper compost safely. Modern inks are soy- or water-based and break down with the paper. Avoid glossy magazines and coated papers, which contain chemicals that do not decompose.