The Basic Rule: Browns and Greens, Nothing Else
Compost works because microorganisms break down organic matter. They need two things: nitrogen-rich materials (greens) and carbon-rich materials (browns). Greens are wet and fresh—grass clippings, vegetable scraps, coffee grounds. Browns are dry and woody—leaves, shredded paper, straw. The pile heats up and breaks everything down when you have both in roughly equal amounts.
The rule that stops most people from making mistakes is straightforward: if it came from a plant or animal and will rot, it probably belongs in compost. If it won't rot, or if it will rot but leave behind something toxic or indigestible, it does not. Meat, dairy, oils, and diseased plants are the main things to keep out.
Key Takeaways
- Vegetable and fruit scraps, coffee grounds, tea bags, grass clippings, leaves, and shredded paper are safe to compost and break down quickly.
- Meat, fish, dairy, oils, fats, and pet waste should never go in a home compost bin because they attract pests or create odor problems.
- Diseased plants, weeds with seeds, and plants treated with pesticides can spread problems to your garden instead of preventing them.
- Glossy or colored paper, treated wood, and synthetic materials do not break down and will sit in your finished compost as trash.
Vegetable and Fruit Scraps You Can Compost
Almost all vegetable and fruit scraps break down well. Carrot peels, onion skins, apple cores, banana peels, lettuce leaves, broccoli stems, squash rinds, and citrus peels all belong in the bin. Chop larger pieces into smaller ones so they break down faster—a whole apple takes longer than apple chunks.
Citrus peels and onion skins are safe despite their strong smell; the smell fades as they decompose. Avocado pits and peach pits take much longer to break down than softer fruit, but they will eventually decompose. If you want faster results, skip the pits or crush them first.
Cooked vegetables are also fine to compost, though raw scraps break down slightly faster. Avoid composting cooked food that has oil, butter, or sauce on it—those are fats, which attract pests and slow decomposition.
Coffee, Tea, and Other Beverage Waste
Coffee grounds and tea bags are among the best things to add to compost. Coffee grounds are nitrogen-rich (a green), so they heat the pile and speed decomposition. Tea bags break down easily, though you should remove any staples or plastic tags first—some tea bags are sealed with plastic instead of glue.
If you use a coffee maker with paper filters, the filters go in too. If you use a metal or mesh filter, just empty the grounds into the bin and compost those. Loose tea leaves go straight in without any container.
Yard Waste: Leaves, Grass, and Wood
Leaves are the backbone of most home compost piles. Shredded leaves break down faster than whole leaves, so run a lawn mower over them if you have time. Grass clippings are nitrogen-rich and heat the pile quickly, but use them in thin layers mixed with browns—a thick mat of grass alone will compact and smell.
Small twigs, wood chips, and sawdust from untreated wood are fine to compost, though they take longer to break down than softer materials. Shredded bark and straw (not hay, which contains seeds) also work well. Avoid treated wood, pressure-treated lumber, and plywood, which contain glues and chemicals that do not break down.
Diseased leaves and diseased plants should not go in a home compost bin. If your tomato plant had blight or your rose had powdery mildew, throw it in the trash instead. Home compost piles do not get hot enough to kill all plant diseases, so you risk spreading the problem to next year's garden.
Paper, Cardboard, and Natural Fibers
Plain paper and cardboard break down well and add carbon to the pile. Shredded newspaper, cardboard boxes (remove tape and staples), paper bags, and plain kraft paper all compost. Tear or shred cardboard into smaller pieces so it breaks down faster.
Do not compost glossy paper, colored paper with heavy inks, or paper coated with plastic or wax. Magazines, junk mail with colored printing, and takeout containers with plastic or wax linings will not break down and will sit in your finished compost as debris. Paper with bleach or heavy chemical inks also stays behind.
Natural fiber items like untreated cotton, wool, and linen can go in, though they take a while. Avoid synthetic fabrics, elastic, and anything with plastic components.
What Never Goes in the Compost Bin
Meat, fish, bones, and any animal product except eggshells will attract rats, raccoons, and flies. Dairy products like milk, yogurt, and cheese also attract pests and create odor. Oils, butter, grease, and fatty foods slow decomposition and smell bad as they break down.
Pet waste—dog or cat feces—should never be composted in a home bin. It can contain pathogens that survive the composting process and contaminate your soil. Use a separate pet waste composter if you want to compost pet waste, or throw it in the trash.
Diseased plants, weeds with mature seeds, and plants treated with pesticides or herbicides do not belong in home compost. The pile does not get hot enough to kill seeds or break down chemical residues. Glossy or colored paper, plastic, synthetic materials, treated wood, and metal also stay in the pile as trash.
Eggshells, Nuts, and Seeds
Eggshells are safe and add calcium to your compost. Rinse them first to remove any egg residue, then crush them into smaller pieces so they break down faster. Whole eggshells take months to decompose, but crushed ones integrate into the pile much quicker.
Nutshells (walnut, almond, peanut) are very hard and take a long time to break down. If you have patience, they will eventually compost, but many people skip them and use them for mulch instead. Seed shells from sunflowers and pumpkins also take a long time.
Do not compost seeds from weeds or diseased plants. Seeds from vegetables you grew are fine if you want them to break down, but many gardeners remove tomato seeds, squash seeds, and bean seeds to save them for next year instead.
Frequently Asked Questions
Can I compost bread, rice, and pasta?
Yes, but sparingly. Bread, rice, pasta, and other grains break down, but they can attract pests and create odor if you add too much at once. Chop them into small pieces and bury them under browns. Use them occasionally rather than as a regular addition.
What about moldy food or rotten produce?
Moldy and rotten food is actually ideal for compost—the mold and bacteria are doing the decomposition work for you. Throw it in without hesitation. The mold will not spread to your garden; it will break down as part of the composting process.
Can I compost weeds from my garden?
Yes, if the weeds have not gone to seed. If they have seed heads or mature seeds, throw them in the trash instead. A home compost pile does not get hot enough to kill all seeds, so you risk spreading weeds through your finished compost.
Is it okay to compost sawdust from my workshop?
Only if the wood is untreated. Sawdust from pressure-treated lumber, plywood, or painted wood contains chemicals that do not break down. Sawdust from untreated pine, oak, or other natural wood is fine and adds carbon to the pile.
Can I put glossy magazines or newspaper in compost?
Plain newspaper yes, glossy magazines no. Glossy paper has a plastic or wax coating that does not break down. It will sit in your finished compost as trash. Colored newspaper with heavy inks is also best avoided.