What Breaks Down and What Doesn't
Compost works because microbes and fungi eat organic matter and turn it into soil. They thrive on nitrogen-rich materials (grass clippings, food scraps) and carbon-rich materials (dry leaves, paper), but they cannot break down plastic, metal, glass, or treated wood. The rule is straightforward: if it came from a plant or animal and has no chemical coating, it probably composts. If it was manufactured, treated, or contains synthetic ingredients, it does not.
The materials that work fastest are soft and moist—fruit and vegetable scraps, fresh grass, coffee grounds. The materials that work slowly are tough and dry—branches, straw, shredded paper. Both types belong in a bin. The materials that never belong are anything that will still be sitting there in five years: bones, dairy, oils, and anything with a label that says "do not compost."
Key Takeaways
- Fruit and vegetable scraps, coffee grounds, eggshells, and grass clippings break down in weeks to months and speed up the whole pile.
- Meat, fish, dairy, oils, and fats attract rats and create odor problems that make composting unpleasant for you and your neighbors.
- Paper and cardboard compost if they have no plastic coating or colored ink, but glossy magazines and wax-coated takeout containers do not.
- Diseased plants, weeds with seeds, and pet waste should not go in home compost because the pile does not get hot enough to kill pathogens.
- Leaves, grass, and wood chips are free carbon sources that balance nitrogen-rich scraps and prevent the pile from smelling like ammonia.
Vegetables, Fruit, and Kitchen Scraps That Compost
Almost all raw fruit and vegetable scraps break down: apple cores, banana peels, carrot tops, lettuce leaves, onion skins, potato peels, squash rinds, and tomato stems. Coffee grounds and tea bags (remove the staple from tea bags first) are nitrogen-rich and compost quickly. Eggshells take longer but do break down. Crushed shells compost faster than whole ones.
Cooked vegetables can go in, but cooked grains and pasta should not—they attract rodents and can create a slimy, anaerobic mess. Nuts and seeds compost, but nut shells (especially black walnut) take years and can inhibit plant growth, so many people leave them out. Citrus peels compost but in large quantities can slow decomposition, so chop them small or add them gradually.
Meat, Fish, Dairy, and Oils to Keep Out
Meat, fish, bones, and any animal product besides eggshells and coffee grounds should not go in a home compost bin. These materials attract rats, raccoons, and flies. They also create a smell that will make neighbors complain. Even if you bury them deep in the pile, rodents will dig them out. If you want to compost animal scraps, you need a specialized hot-composting system or a commercial facility that reaches high enough temperatures to kill pathogens and deter pests.
Dairy products—milk, cheese, yogurt, butter—also attract rodents and create odor. Oils, grease, and fat do not break down in a home bin and can create a waterproof layer that stops air flow. Avoid cooking oil, salad dressing, mayonnaise, and fatty meat trimmings. If you have a small amount of oil on a plate, rinse it off before composting the plate scraps.
Paper, Cardboard, and Wood Products
Plain paper, cardboard, and corrugated boxes compost well and add carbon to balance nitrogen-rich scraps. Shred or tear them into small pieces so they break down faster. Newspaper, paper bags, and paper towels all work. Avoid glossy magazines, colored cardboard with heavy inks, and anything with a plastic or wax coating—pizza boxes have a grease-resistant coating on the inside, so compost only the plain outer box.
Wood chips, sawdust, and untreated wood shavings compost slowly but do break down. Avoid treated wood, plywood, and anything that has been painted or stained. Branches thicker than a pencil take years to decompose, so chip them first if you have a chipper, or leave them out and use them as mulch instead. Sawdust from pressure-treated lumber or composite wood contains chemicals and should never be composted.
Grass, Leaves, and Garden Waste
Fresh grass clippings, dry leaves, and plant trimmings are the backbone of most home compost piles. Grass is nitrogen-rich and heats up the pile quickly. Leaves are carbon-rich and balance the nitrogen. Mix them in layers—a few inches of grass, then a few inches of leaves, then scraps, then repeat. This layering speeds decomposition and prevents the pile from becoming a matted, smelly mess.
Do not compost diseased plants, plants infected with fungal or bacterial problems, or weeds that have gone to seed. Home compost piles do not reach the temperature needed to kill pathogens or destroy seeds. If you compost diseased tomato plants, you will spread the disease to next year's garden. Weeds with mature seed heads will germinate in your finished compost and spread throughout your yard. Bag these materials and put them in the trash or yard waste bin instead.
Synthetic Materials and Treated Products
Plastic, metal, glass, and rubber do not compost and should never go in the bin. This includes plastic bags (even "compostable" ones, unless your facility specifically accepts them), plastic wrap, rubber bands, and twist ties. Compostable packaging labeled for industrial facilities will not break down in a home pile—it needs the heat and conditions of a commercial composter. Read the label: if it says "industrial composting only," leave it out.
Treated wood, pressure-treated lumber, and composite wood products contain chemicals that do not break down and can contaminate your finished compost. Glossy or colored paper, stickers, and labels should be removed before composting. Synthetic fertilizers, pesticides, and herbicides do not belong in compost. If you want to add nutrients, use finished compost or aged manure from herbivores (horse, cow, chicken), not from pets or humans.
Pet Waste and Human Waste
Dog and cat feces should not go in home compost. They contain pathogens that can survive the composting process and contaminate vegetables you grow. Cat litter, even if it is labeled "flushable" or "compostable," should not be composted at home. Used cat litter can harbor toxoplasma, a parasite that poses a risk to pregnant people and immunocompromised individuals.
Human waste and soiled diapers do not belong in home compost for the same reason—the pile does not get hot enough to kill pathogens. If you want to compost human waste, you need a specialized system designed for that purpose. Urine can be added to compost in small amounts and actually speeds decomposition, but feces should not be.
Frequently Asked Questions
Can I compost bread, pasta, and rice?
Cooked bread, pasta, and rice should not go in a home bin because they attract rodents and can create a slimy, anaerobic layer. Raw grains and seeds compost, but slowly. If you have leftover cooked food, throw it in the trash or use a commercial composting service that accepts cooked food.
What about sawdust from my workshop?
Sawdust from untreated wood composts fine and adds carbon to the pile. Sawdust from pressure-treated lumber, plywood, or composite materials contains chemicals and should not be composted. If you are unsure whether the wood was treated, leave the sawdust out.
Can I compost weeds if I remove the seeds?
Weeds compost, but removing every seed is nearly impossible. If the weeds have not flowered yet, you can compost them. If they have gone to seed, bag them instead. The risk is not worth it—one missed seed head can spread weeds throughout your garden next year.
Is it okay to put a small amount of meat in the compost?
No. Even a small amount of meat, fish, or bone will attract rodents. Home compost piles are not hot enough to kill the bacteria that grow on animal products. If you have meat scraps, throw them in the trash or use a commercial composting service.
Can I compost coffee filters and tea bags?
Yes, both compost well. Remove the staple from tea bags first—it does not compost. Some tea bags have a plastic component, so check the packaging. If the bag is labeled as compostable, it will break down in your pile.