The Basic Rule: Browns and Greens, Nothing Else

Your compost pile breaks down two types of material: greens (nitrogen-rich, wet things like food scraps and grass clippings) and browns (carbon-rich, dry things like leaves and shredded paper). Anything that fits one of those categories and will rot without creating smell, pests, or toxic fumes can go in. Everything else stays out — and that's a shorter list than most people think.

The reason is straightforward: compost works through decomposition, and decomposition has limits. Meat, dairy, and oils don't decompose the way plant matter does — they attract rats and flies, create odors that upset neighbors, and can harbor pathogens. Treated wood, glossy paper, and synthetic materials don't decompose at all. Diseased plants and weeds with seeds spread problems instead of solving them. Knowing what belongs in your bin keeps the pile healthy and your compost actually usable.

Key Takeaways

  • Greens include fruit and vegetable scraps, coffee grounds, grass clippings, and plant trimmings; browns include dry leaves, shredded newspaper, cardboard, and wood chips.
  • Never add meat, fish, dairy, oils, fats, or cooked food — these attract pests and create odor problems that make neighbors complain.
  • Keep out diseased plants, weeds with seeds, pet waste, glossy or colored paper, treated wood, and anything synthetic.
  • The ratio matters: aim for roughly three parts brown to one part green by volume, adjusting if your pile smells or stays too wet.

Greens You Can Add

Greens are the wet, nitrogen-rich materials that heat up your pile and feed the microbes doing the work. Raw fruit and vegetable scraps are the most common: apple cores, banana peels, carrot tops, lettuce, broccoli stems, onion skins, and potato peels all break down quickly. Coffee grounds and tea bags (remove the staple if there is one) add nitrogen and moisture. Grass clippings work, but only if your lawn has not been treated with herbicide or pesticide — check with whoever maintains it if you are not sure.

Plant trimmings from your garden go in as long as the plant was healthy. Crushed eggshells add calcium and break down slowly, which is fine — they just take longer. Fresh manure from herbivores (horses, cows, rabbits, chickens) is a strong green, but aged manure is safer because fresh manure can harbor pathogens. Never use cat or dog waste; it carries parasites that compost temperatures do not reliably kill.

Browns You Can Add

Browns are the dry, carbon-rich materials that give your pile structure and prevent it from becoming a soggy mat. Dry leaves are the easiest source — shred them first if you can, because whole leaves mat down and slow decomposition. Shredded newspaper and cardboard (remove tape and labels) break down well; plain newsprint is fine, but avoid glossy inserts and colored sections. Straw and hay work, though hay may contain weed seeds — straw is safer.

Wood chips and sawdust from untreated wood are acceptable, but use them sparingly because they decompose slowly and can tie up nitrogen. Shredded paper from a paper shredder is fine as long as it is not colored or coated. Paper bags, paper towels, and napkins (unsoiled) can go in. Avoid anything treated with chemicals: pressure-treated wood, plywood, particle board, and anything that has been stained or sealed will not break down and may leach toxins into your finished compost.

What Never Goes In

Meat, fish, bones, and any animal product except manure and eggshells will rot in ways that attract rats, raccoons, and flies. Dairy products (milk, cheese, yogurt, butter) do the same. Oils, fats, and grease coat other materials and slow decomposition while creating odor. Cooked food of any kind is risky because it can harbor pathogens and attracts pests more than raw scraps do.

Diseased plants and weeds with mature seeds should not go in unless your pile reaches and holds 140°F (60°C) for at least two weeks — most home piles do not. Diseased material spreads the problem to your garden when you use the finished compost. Pet waste (cat litter, dog feces) carries parasites that survive typical compost temperatures. Glossy or colored paper, treated wood, plywood, and anything synthetic (plastic, rubber, metal) will not decompose and contaminates your finished product.

The Smell and Pest Problem

If your pile smells like rotting meat or ammonia, something wrong is in there or your ratio is off. Ammonia smell means too many greens and not enough browns — add dry leaves or shredded paper. Rotting meat smell means meat or dairy got in; remove what you can and bury it under a thick layer of browns. If rats or flies appear, the same rule applies: remove the attractant and cover everything with at least 6 inches of brown material.

The easiest way to avoid this is to keep a small container in your kitchen for scraps and empty it into the bin regularly rather than leaving it exposed. Bury food scraps under browns when you add them. If you live in a place with bears or aggressive wildlife, a closed bin or tumbler is safer than an open pile.

Getting the Ratio Right

The ideal ratio is roughly three parts brown to one part green by volume — that is, three buckets of dry leaves to one bucket of grass clippings. This ratio keeps the pile from becoming waterlogged while providing enough nitrogen to heat up and decompose. If your pile stays wet and smells, add more browns. If it dries out and stops breaking down, add more greens or water it lightly.

You do not need to measure precisely. Just aim for a pile that looks like it has more brown material than green, and adjust based on what you see. A healthy pile should feel like a wrung-out sponge — moist but not dripping — and should not smell bad. If it does, the fix is usually more browns or better mixing.

Frequently Asked Questions

Can I compost citrus peels and onions?

Yes, both break down fine. Citrus peels take longer than softer scraps, and some people worry they slow decomposition, but they do not — they just sit there longer before breaking down. Onions and garlic are safe too, though some gardeners say they can repel worms if you are vermicomposting.

What about bread, pasta, and rice?

Cooked bread, pasta, and rice can attract pests the same way meat does, so it is safer to avoid them. Raw flour and uncooked grains are fine in small amounts, but they also attract rodents. If you add them, bury them deep under browns.

Can I put weeds in if I pull them before they seed?

Yes, as long as they have not flowered or set seed. Once a weed flowers, seeds may already be developing inside even if you cannot see them yet. When in doubt, leave it out — it is not worth spreading weeds through your garden.

Is it okay to add sawdust from my workshop?

Only if the wood is untreated. Sawdust from pressure-treated lumber, plywood, or anything stained or sealed will contaminate your compost. If you are not certain what the wood was treated with, do not use it.

Can I compost paper with ink on it?

Plain newsprint and black ink are fine. Glossy paper, colored inks, and anything with a plastic coating should stay out. When in doubt, shred it and smell it — if it smells chemical, leave it out.