Never compost meat, fish, dairy, or oils
Meat, fish, bones, and dairy products break down slowly and attract rats, raccoons, and flies to your compost bin. They create odor problems that spread beyond your yard. Even small amounts — a chicken bone, a spoonful of yogurt, a pat of butter — will draw pests and make your pile smell like rotting garbage instead of earth.
Oils and grease coat other materials and slow decomposition. They also create a waterproof layer that prevents air from reaching the center of your pile, which kills the microbes that do the actual composting work. Avoid cooking oils, salad dressings, mayonnaise, and fatty meat scraps.
If you want to compost food scraps, stick to fruit and vegetable peels, coffee grounds, eggshells, and plant trimmings. These break down quickly and do not attract large animals.
Key Takeaways
- Meat, fish, bones, and dairy products attract rodents and create strong odors that spread to your neighbors' yards.
- Oils and grease slow decomposition and create waterproof barriers that prevent air circulation in your pile.
- Diseased plants, weeds with seeds, and treated wood introduce problems that survive the composting process and spread to your garden.
- Glossy or colored paper, plastic, and synthetic materials do not break down and will remain in your finished compost as fragments.
- Pet waste and human feces carry pathogens that survive home composting temperatures and pose health risks.
Do not add diseased plants or weeds with mature seeds
If a plant in your garden had powdery mildew, blight, or fungal disease, do not put it in your compost pile. Home compost piles do not reach temperatures high enough to kill plant diseases. When you spread that finished compost on your garden beds next year, you will reintroduce the same disease to your soil.
Weeds that have already gone to seed are another problem. Composting does not reliably destroy weed seeds. You may think you are composting a pile of dead weeds, but when you spread that compost, you are actually spreading thousands of seeds that will germinate in your beds. Pull weeds before they flower, or throw mature weeds in the trash instead.
Diseased leaves, stems, and roots should go in your yard waste bin if your municipality collects it, or in the trash. Your compost pile is for healthy plant material only.
Keep out treated wood, glossy paper, and synthetic materials
Pressure-treated wood, plywood, and composite lumber contain chemicals designed to resist rot and insects. These chemicals do not break down in a home compost pile — they persist in the finished compost and eventually end up in your soil and plants. Do not add sawdust from treated wood, wood chips from construction waste, or old wooden pallets unless you know they were never treated.
Glossy or colored paper, cardboard with plastic coating, and paper with ink printed directly on it should not go in your pile. The inks and coatings do not decompose. Shredded newspaper and plain cardboard are fine, but avoid anything that feels waxy or has a plastic-like finish.
Plastic, synthetic fabrics, rubber, and foam never break down in a home compost pile. Even "compostable" bags labeled for industrial composting will not decompose in your backyard bin — they require the high heat of a commercial facility. Stick to natural materials: paper, cardboard, leaves, grass, and plant scraps.
Never add pet waste or human feces
Dog and cat feces contain parasites and pathogens that survive home composting temperatures. Even if your pile reaches 140°F, which most backyard piles do not, that temperature must be maintained for several weeks to kill these organisms. When you spread that compost on vegetables or herbs, you risk contaminating your food with harmful bacteria and parasites.
Human feces and urine should never go into a standard compost pile for the same reason. If you have a composting toilet, it requires a separate system designed specifically to handle human waste safely — not a regular compost bin.
Pet waste from litter boxes, poop bags, and soiled bedding all belong in the trash. Your compost pile is for plant material and food scraps only.
Avoid coal ash, charcoal, and glossy magazines
Wood ash from a fireplace or wood stove is fine in small amounts, but coal ash and charcoal ash contain substances that harm soil and plants. If you are not certain what fuel was burned, do not add the ash to your pile.
Glossy magazines, junk mail with colored inks, and paper with plastic windows do not belong in compost. The inks and coatings persist through decomposition. Stick to plain newsprint and uncoated cardboard.
Sawdust from pressure-treated lumber, MDF, or particle board should be kept out. Sawdust from untreated hardwood is acceptable in small quantities, but if you are buying it, verify the source first.
Do not compost synthetic fertilizers or pesticide-treated materials
Grass clippings from a lawn that was recently treated with herbicide or pesticide should not go into your compost pile. These chemicals persist through decomposition and will end up in your finished compost. Wait at least two weeks after a pesticide process before adding grass clippings to your pile, and check the product label for specific guidance.
Synthetic fertilizers do not belong in compost — they are already processed and do not need to break down further. Adding them serves no purpose and can create nutrient imbalances in your finished compost.
If you are unsure whether a material was treated, ask the source or leave it out. It is better to throw something away than to contaminate your entire compost pile.
What happens if you add the wrong materials
Adding meat or dairy creates an when ready pest problem and odor that can last for weeks. Your neighbors will notice, and you may find yourself dealing with rats or raccoons in your yard.
Adding diseased plants or weed seeds means you are spreading problems to your garden beds when you use the finished compost. You will spend next season fighting the same diseases and weeds you thought you had composted.
Adding plastic, treated wood, or synthetic materials means your finished compost will contain fragments that do not break down. You will be spreading these fragments into your garden beds, where they persist indefinitely. Plastic fragments can harm soil structure and plant roots over time.
The safest approach is to compost only what you are certain about: fruit and vegetable scraps, coffee grounds, eggshells, leaves, grass clippings from untreated lawns, and shredded plain cardboard. If you are not sure, throw it in the trash.
Frequently Asked Questions
Can I compost bread, pasta, or cooked food?
Cooked food, bread, and pasta attract pests the same way meat and dairy do. Stick to raw fruit and vegetable scraps. If you want to compost bread or pasta, bury it deep in the center of a very large pile where pests cannot easily reach it, but this is not recommended for small backyard bins.
What about citrus peels and onion scraps?
Citrus peels and onion scraps are fine in compost, though some gardeners report that large amounts of citrus can slow decomposition slightly. Add them in moderation mixed with other materials, and they will break down without problems.
Is it safe to compost leaves from a diseased tree?
No. Leaves from trees with fungal diseases, blight, or pest infestations should go in the trash or yard waste bin. The disease will survive in your compost pile and spread when you use the finished product.
Can I compost paper with black ink?
Yes. Black ink from newspapers and plain printed paper is safe to compost. Avoid glossy magazines, colored inks, and anything with a plastic coating.
What if I accidentally added meat to my pile?
Remove it if you can find it. If it is already mixed in, turn your pile frequently to speed decomposition and watch for pest activity. You may need to cover the pile with a tight-fitting lid or hardware cloth to keep animals out while it breaks down.