Materials That Will Damage Your Compost or Attract Pests
Not everything organic breaks down safely in a home compost bin. Meat, fish, dairy, oils, and fats decompose slowly, create foul odors, and draw rats and raccoons to your pile. Pet waste (especially from cats and dogs) contains harmful pathogens that compost temperatures rarely reach high enough to kill. Diseased plants can spread infections to your garden soil when you use the finished compost.
Cooked food scraps are riskier than raw ones because the cooking process can concentrate certain compounds and attract more pests. Bones take years to break down and often never fully decompose in a backyard bin. Grease and cooking oil coat other materials and slow decomposition to a crawl.
Glossy or coated paper—like takeout containers, pizza boxes with grease stains, or magazine pages—contains chemicals that do not break down naturally. The coating prevents the paper from absorbing moisture and integrating into the pile.
Key Takeaways
- Meat, fish, dairy, oils, and fats attract rodents and create odor problems that can last for months.
- Pet waste and diseased plant material introduce pathogens that home compost piles do not get hot enough to eliminate.
- Glossy paper, plastic, and treated wood contain chemicals that do not decompose and will contaminate your finished compost.
- Sawdust from pressure-treated wood and coal or charcoal ash contain toxic compounds that persist in soil.
- Synthetic materials like rubber, plastic, and synthetic fabrics will remain in your pile indefinitely and break into microplastics.
Synthetic Materials and Treated Products
Plastic bags—even those labeled "compostable"—do not break down in most home bins because they require industrial composting temperatures (around 140°F or higher) that backyard piles rarely reach. The same applies to compostable food containers and cutlery. Rubber, synthetic fabrics, and nylon will sit in your pile for years without decomposing.
Pressure-treated wood and plywood contain copper, arsenic, or other preservatives that leach into soil and can harm plants. Sawdust from these materials is especially problematic because it spreads the toxins throughout the pile. Regular untreated wood chips decompose fine, but treated lumber does not belong in compost.
Charcoal and coal ash differ from wood ash. Wood ash from a fireplace or untreated wood fire can go in compost in small amounts, but charcoal briquettes and coal ash contain additives and chemicals that do not break down.
Plants and Weeds That Spread Problems
Weeds with mature seeds will survive the composting process and germinate in your garden when you spread the finished compost. If you are not certain whether a weed has gone to seed, leave it out. Invasive plants like bindweed, Japanese knotweed, or bermuda grass can regrow from even tiny root fragments in your pile.
Plants infected with fungal diseases (like powdery mildew or early blight on tomatoes) or bacterial wilts should not go in a home compost bin. The pile may not reach temperatures high enough to kill the pathogens, and you will spread the disease back to your garden. Diseased leaves are safer to burn or throw away.
Black walnut leaves and twigs contain a compound called juglone that inhibits the growth of many plants. Composting them does not eliminate this toxin, so they are better left out of the pile.
Paper, Cardboard, and Wood Products to Avoid
Newspaper and plain cardboard break down fine, but glossy paper, wax-coated cardboard, and laminated materials do not. Takeout containers, pizza boxes with grease, and shiny magazine pages all contain coatings that prevent decomposition. The coating also prevents water from penetrating the material, so it sits in your pile unchanged.
Colored cardboard and paper printed with soy-based inks are usually safe, but if you are unsure whether the ink or coating is synthetic, leave it out. Thermal paper (like receipts) contains chemicals that do not decompose and can leach into soil.
Stickers, tape, and labels should be removed from cardboard before composting. The adhesive does not break down and will remain in your finished compost as small plastic fragments.
Yard Waste That Causes Problems
Grass clippings treated with herbicides or pesticides will carry those chemicals into your compost and eventually into your soil and food. If you use lawn chemicals, let the grass dry for a few days after treatment before adding clippings to the pile, or skip them entirely. Leaves from treated ornamental plants (those sprayed for insects or disease) should also be avoided.
Branches thicker than a pencil take a very long time to decompose in a home bin and can jam up the pile. Shredding them first helps, but if you do not have a shredder, a brush pile or curbside yard waste collection is a better option. Pine needles and conifer needles are acidic and decompose slowly, so use them sparingly.
Unusual Items People Often Try to Compost
Dryer lint sounds like it should compost, but most lint contains synthetic fibers from clothing that do not break down. Lint from natural fibers (cotton, wool) is fine in small amounts, but you cannot easily tell the difference, so it is safer to skip it. Vacuum cleaner bags contain the same problem plus trapped chemicals from cleaning products.
Glossy photographs, receipts, and paper with colored ink should not go in compost. The inks and coatings do not decompose. Sawdust from sanding or cutting treated wood is especially dangerous because it spreads toxins throughout the pile in fine particles.
Citrus peels in large quantities can slow decomposition and repel earthworms because of their acidity and oils. A few peels are fine, but do not add whole bags of them. Onion and garlic scraps in large amounts can also repel worms and create odor problems.
What to Do With Materials You Cannot Compost
Meat, fish, and dairy can go into municipal composting programs in many cities, which reach higher temperatures than home bins. Check whether your local program accepts these materials before putting them in your cart. If your area does not have municipal composting, a garbage disposal or trash bin is the safest option.
Pet waste should go in the trash or a dedicated pet waste composter (which is separate from food compost). Diseased plants can be burned if local regulations allow, or bagged and thrown away. Treated wood and synthetic materials belong in the trash or recycling (if the material is recyclable).
Weeds with seeds and invasive plant fragments are worth the effort to remove from your compost pile before they cause problems in your garden. If you have already added them, monitor your finished compost for sprouting seedlings and remove them by hand.
Frequently Asked Questions
Can I compost bread, pasta, and cooked grains?
Raw grains and uncooked pasta are fine in small amounts, but cooked versions attract pests more readily and decompose unevenly. If you add them, bury them deep in the pile and cover with brown materials like leaves or cardboard. Bread mold is not a problem, but the bread itself can attract rodents.
Is it safe to compost paper towels and napkins?
Plain white paper towels and napkins without bleach break down fine. Avoid those with printed patterns, colored dyes, or plastic reinforcement. If you are unsure about the product, plain newspaper is a safer alternative.
What about eggshells and coffee grounds?
Both are excellent for compost. Eggshells add calcium and take a few months to break down completely, but that is normal. Coffee grounds and filters (if unbleached) decompose quickly and add nitrogen to the pile.
Can I compost hair and nail clippings?
Human hair and fingernail clippings decompose very slowly and can mat together in the pile, blocking airflow. They are not harmful, but they do not add much value to compost. Pet fur is fine in small amounts if it is not treated with flea or tick medication.
What if I accidentally added something I should not have?
If you added meat or dairy, remove it if you can find it and cover the area with extra brown materials to reduce odor. If you added treated wood or plastic, remove those items before using the finished compost. Small amounts of glossy paper or coated cardboard will not ruin a batch, but pick out larger pieces before spreading the compost in your garden.