Browns and Greens: The Two Categories That Matter
A working compost bin needs two types of material: browns (carbon-rich) and greens (nitrogen-rich). Browns are dry: shredded paper, cardboard, dried leaves, straw, and wood chips. Greens are wet or fresh: grass clippings, vegetable scraps, coffee grounds, and plant trimmings. The pile breaks down fastest when you layer them roughly equally — aim for about one part green to two parts brown by volume, though exact ratios are forgiving.
Browns decompose slowly but give the pile structure and air pockets. Greens decompose quickly and heat the pile. Without enough browns, your bin becomes a wet, smelly mess. Without enough greens, nothing much happens. Most home composters struggle because they add too many greens and not enough browns — if your bin smells like ammonia or rotten eggs, you need more dry material.
Key Takeaways
- Vegetable and fruit scraps, coffee grounds, and crushed eggshells are safe greens; meat, fish, dairy, and oils will attract pests and should stay out.
- Shredded paper, cardboard, dried leaves, and wood chips are the browns that balance greens and keep the pile from becoming waterlogged.
- Diseased plants, weeds with seeds, and pet waste do not belong in a home compost bin because they survive the decomposition process.
- Glossy paper, treated wood, and synthetic materials do not break down and will contaminate your finished compost.
- Grass clippings are green material, but only if they have not been treated with herbicide or pesticide.
Vegetable and Fruit Scraps You Can Add
Vegetable peels, cores, stems, and trimmings all go in. Fruit scraps — apple cores, banana peels, citrus rinds, melon rinds — break down well. Onion and garlic skins are fine. Stale bread, cooked rice, and pasta (in small amounts) will compost, though they can attract rodents if not buried under browns. Coffee grounds and tea bags (remove the staple if it has one) are nitrogen-rich and decompose quickly.
Crushed eggshells add calcium and take months to break down fully, but they do not harm the pile. Avoid adding them whole — crush them first so they decompose faster. Nut shells (except walnut shells, which contain a substance that inhibits plant growth) are fine but decompose very slowly, so expect them to still be visible in finished compost.
What to Keep Out: Meat, Dairy, and Oils
Do not add meat, fish, bones, or any animal product except eggshells and manure from herbivores. These attract rats, raccoons, and flies and create odor problems that take weeks to resolve. Dairy products — milk, cheese, yogurt, butter — also attract pests and can create a foul smell. Cooking oils and grease do the same and slow decomposition by coating other materials.
If you have a sealed, rodent-proof bin and live somewhere without wildlife pressure, you might get away with small amounts of cooked food scraps buried deep under browns. Most home composters should not attempt this. The smell and pest problems are not worth the small amount of finished compost you gain.
Paper, Cardboard, and Wood Materials
Shredded newspaper, cardboard boxes (remove tape and staples), paper bags, and paper towels are all acceptable browns. Cardboard breaks down faster if you wet it first and tear it into smaller pieces. Avoid glossy or coated paper — the coating does not decompose and will remain in your finished compost. Newspaper printed with soy-based ink is fine; older papers with heavy metal inks are rare now but worth avoiding if you know the source.
Wood chips, sawdust, and untreated wood shavings work well, though they decompose slowly — expect them to still be visible after six months. Never add treated wood, plywood, or particle board, which contain glues and chemicals that do not break down. Pine needles are acidic and decompose very slowly; use them sparingly if at all.
Yard Waste: Leaves, Grass, and Plant Trimmings
Dried leaves are one of the best browns you can add — shred them if possible so they pack down less. Fresh grass clippings are green material and heat the pile quickly, but only use them if they have not been treated with herbicide or pesticide. If you are unsure about the lawn's history, leave the grass out. Plant trimmings and prunings from ornamental plants are fine as long as they are not diseased.
Do not add diseased plant material — fungal infections, mildew, and bacterial wilts survive the composting process and will spread to your garden when you use the finished compost. If a plant had powdery mildew, blight, or root rot, throw it in the trash instead. Weeds are acceptable only if they have not yet set seed; if the seed heads are visible, leave them out because most home compost piles do not get hot enough to kill seeds.
Materials That Do Not Belong
Pet waste (dog or cat feces) should never go in a home compost bin. It can harbor parasites and pathogens that survive composting and contaminate vegetables you grow. Horse, chicken, and cow manure are safe and actually beneficial — they add nitrogen and microbes. Sawdust from treated lumber, pressure-treated wood, and anything painted or stained will leach chemicals into your compost.
Synthetic materials — plastic, rubber, nylon, polyester — do not decompose and will remain in your finished compost forever. This includes tea bags with plastic mesh, coffee pods, and compostable-labeled items that require industrial composting (not home bins). Charcoal and coal ash contain substances that inhibit plant growth; wood ash in small amounts is acceptable, but do not add more than a thin layer at a time.
How to Layer for Faster Breakdown
The fastest way to compost is to layer: a few inches of browns, then a few inches of greens, then browns again. Water each green layer lightly as you go — the pile should feel like a wrung-out sponge, not soggy. Turn the pile every week or two if you want finished compost in two to three months. If you do not turn it, expect four to six months or longer.
Shred or chop materials before adding them — smaller pieces have more surface area and decompose faster. A pile that is at least 3 feet by 3 feet by 3 feet will heat up and decompose faster than a smaller one. If your bin is smaller, be patient and do not expect the speed of a large pile.
Frequently Asked Questions
Can I compost citrus peels and onion skins?
Yes. Citrus peels and onion skins break down normally. Some gardeners avoid large amounts of citrus because the acidity can slow decomposition slightly, but small quantities are fine. Bury them under browns so they do not attract fruit flies.
What about sawdust from my workshop?
Only if it is from untreated wood. Sawdust from pressure-treated lumber, plywood, or finished wood contains glues and chemicals that do not decompose. If you are unsure whether the wood was treated, leave the sawdust out.
Can I add weeds to my compost?
Only if they have not flowered or set seed. Once a weed has visible seed heads, the seeds usually survive home composting and spread when you use the finished compost. If you are not certain, throw the weeds in the trash instead.
Is it okay to add a little bit of meat or fish?
No. Even small amounts attract rodents and create odor problems that take weeks to resolve. Stick to plant material and herbivore manure.
What if my compost smells bad?
A rotten-egg or ammonia smell means too much green material and not enough brown. Add shredded paper, cardboard, or dried leaves and mix the pile. A foul, meaty smell means you added something that should not be there — dig it out if you can identify it.