Most food scraps and yard waste break down in a compost pile, but not everything

You can compost fruit and vegetable scraps, coffee grounds, tea bags, crushed eggshells, grass clippings, leaves, small branches, and shredded paper or cardboard. You cannot compost meat, fish, dairy, oils, pet waste, diseased plants, or glossy paper. The difference comes down to what attracts pests, what takes years to break down, and what introduces pathogens that home composting temperatures cannot kill.

Your compost pile works because bacteria and fungi eat organic matter and generate heat. That process works fast on soft materials like vegetable peels and grass. It stalls or fails on materials that are too dense, too oily, or too toxic for those microorganisms to handle. Some items, like meat and dairy, will technically break down eventually — but they will smell terrible and draw rats and flies long before they do.

Key Takeaways

  • Fruit and vegetable scraps, coffee grounds, crushed eggshells, grass clippings, and leaves are safe to compost and break down quickly.
  • Meat, fish, dairy, oils, fats, and pet waste should never go in a home compost pile because they attract pests and create odor problems.
  • Diseased plants and weeds with seeds will spread problems to your garden instead of preventing them.
  • Glossy or coated paper, treated wood, and synthetic materials do not break down and can introduce chemicals into your finished compost.

What breaks down fast and safely

Vegetable and fruit scraps are the foundation of most home compost piles. Carrot peels, apple cores, lettuce leaves, onion skins, and banana peels all break down within weeks to a few months. Coffee grounds and tea bags (remove the staple from tea bags first) add nitrogen and break down easily. Crushed eggshells take longer but add calcium and do not cause problems.

Yard waste makes up the bulk of many piles. Grass clippings, leaves, small twigs, and plant stems all decompose. Shredded newspaper and plain cardboard (no tape or labels) add carbon and help balance nitrogen-heavy food scraps. The key is mixing: a pile of only grass will mat down and smell; a pile of only leaves will take years. Alternate layers of "green" materials (food scraps, fresh grass) with "brown" materials (dried leaves, shredded paper) to keep air moving through.

What attracts pests and creates odor

Meat, fish, bones, and any animal product will decompose, but not in a way that works for home composting. These materials attract rats, raccoons, and flies. They also smell strongly as they break down — a sour, rotten smell that can upset neighbors and make your yard unpleasant. The bacteria that eat meat produce different byproducts than the bacteria that eat plants.

Dairy products, oils, fats, and grease have the same problem. Cheese, milk, butter, and cooking oil will eventually break down, but they create odor and attract pests first. They also slow decomposition because they coat other materials and block air from reaching the bacteria that do the work. If you have a lot of cooking oil, it belongs in the trash or a grease disposal, not the pile.

Pet waste — dog or cat feces — should never be composted at home. It contains pathogens that home piles do not get hot enough to kill. Even if the pile reaches 140°F (which most home piles do not), pet waste needs sustained heat above 165°F for weeks. Use a separate pet waste composter if you want to handle it, or throw it in the trash.

Plants and seeds that cause problems

Do not compost plants that are visibly diseased — those with mold, fungal spots, wilting from disease, or pest damage. Home compost piles do not get hot enough to kill most plant diseases. If you compost a diseased tomato plant, you may spread that disease to your garden when you use the finished compost. The same applies to weeds that have gone to seed. Composting kills some seeds, but not all, and you may end up spreading weeds instead of preventing them.

Diseased or seedy material belongs in the trash or a yard waste bin that gets taken to a commercial facility. Commercial composting reaches higher temperatures and longer timescales than home piles, so it can handle these materials safely.

Paper, cardboard, and treated materials

Plain cardboard and newspaper break down and add carbon to your pile. Shred them into strips so they decompose faster. Avoid glossy paper, coated cardboard, and anything with colored ink or plastic coating. Glossy magazines, takeout containers with plastic lining, and wax-coated boxes do not break down in a home pile and can introduce chemicals into your finished compost.

Never compost treated wood, plywood, or sawdust from treated lumber. These materials are coated with chemicals to resist rot and insects, and those chemicals will end up in your compost and then in your soil. Untreated wood chips and sawdust from untreated wood are fine, but treated wood is not.

Synthetic materials and other items to avoid

Plastic, rubber, synthetic fabrics, and metal do not belong in compost. They do not break down in a home pile and will remain in your finished compost as fragments. Even "compostable" bags and utensils marked for industrial composting will not break down in a home pile — they need the higher heat and longer timescale of a commercial facility.

Coal and charcoal ash should not go in compost. Wood ash from a fireplace or wood stove is fine in small amounts, but coal ash contains substances that can harm plants. Sawdust from pressure-treated wood, as mentioned above, also belongs in the trash.

How to handle items you are unsure about

If you are not sure whether something will compost, the safest rule is: if it came from an animal or was made by a person, think twice. Plant material almost always works. Anything that smells strong, is oily, or is synthetic probably does not. When in doubt, throw it in the trash rather than risk attracting pests or slowing your pile.

Keep a small container near your kitchen for compost scraps so you do not have to think about each item as you cook. Most households find that fruit and vegetable scraps, coffee grounds, and eggshells make up the bulk of what they compost. That alone will build a working pile over time.

Frequently Asked Questions

Can I compost citrus peels and onions?

Yes, citrus peels and onion skins compost fine. They take a bit longer than softer scraps, but they break down. Some people worry that citrus slows decomposition, but the effect is small unless you add huge amounts. Chop them into smaller pieces to speed things up.

What about bread, pasta, and cooked food?

Plain bread and cooked pasta can go in compost, but they attract pests the same way meat does. If you want to compost them, bury them deep in the pile under leaves or grass so they are not visible. Cooked food with oil, sauce, or meat should go in the trash.

Can I compost weeds if I pull them before they seed?

Yes, if the weeds have not flowered or set seed, they are safe to compost. Once a weed has flowers or visible seed heads, do not compost it. If you are not sure whether seeds are present, throw the weeds in the trash instead.

Is it okay to compost glossy junk mail?

No. Glossy paper is coated with plastic and chemicals that do not break down in a home pile. Stick to plain newspaper and uncoated cardboard. Shred them to speed decomposition.

What if I accidentally put meat in my compost?

Remove it if you can see it. If it is already mixed in, bury it deep under several inches of leaves or grass and watch for pest activity over the next week or two. If you see rats or flies, you may need to remove that section of the pile and put it in the trash.