Materials That Will Ruin Your Compost

Meat, fish, dairy, oils, and grease belong in the trash, not the compost bin. These materials break down slowly, attract rodents and insects to your pile, and create foul odors that can persist for months. Even small amounts — a spoonful of butter, a piece of chicken skin — will draw pests and upset the balance of your compost.

Pet waste (dog or cat feces) and diseased plants also go to the trash. Pet waste carries pathogens that survive composting temperatures and can contaminate your finished compost. Diseased plants spread fungal infections and plant viruses to your garden when you use the compost later.

Glossy or coated paper, including magazine pages and takeout containers with plastic or wax coating, will not break down in a home compost bin. The coating prevents decomposition and can leach chemicals into your soil. Newspaper and plain cardboard are safe; glossy paper is not.

Key Takeaways

  • Meat, fish, dairy, oils, and grease attract rodents and create odor problems that can last for months.
  • Pet waste and diseased plants introduce pathogens and plant viruses that survive the composting process.
  • Glossy paper, plastic-coated cardboard, and synthetic materials do not decompose in home compost bins.
  • Treated wood, charcoal ash, and synthetic fabrics contain chemicals or persist unchanged in finished compost.
  • Weeds with mature seeds and invasive plants can spread to your garden when you use the finished compost.

Why Synthetic Materials and Treated Products Fail

Plastic, rubber, and synthetic fabrics do not break down in compost. They will sit in your pile unchanged and end up in your finished compost, where they fragment into microplastics that persist in your soil. This includes plastic bags, even those labeled "compostable" unless your local industrial composting facility accepts them — home bins do not reach the required temperature.

Treated wood, pressure-treated lumber, and plywood contain chemical preservatives or glues that leach into compost and then into your garden soil. Charcoal ash (from grills or fireplaces) contains substances that can harm plants, unlike wood ash from untreated wood, which is safe in small amounts. Synthetic dyes in colored paper and cardboard can also persist and contaminate soil.

Seeds, Weeds, and Plants to Keep Out

Weeds with mature seeds will survive composting and sprout in your garden when you spread the finished compost. If you are unsure whether a weed has gone to seed, throw it in the trash instead. Invasive plants like bindweed, bermuda grass, and morning glory roots can regenerate from fragments in compost and spread aggressively through your garden beds.

Black walnut leaves and twigs contain a chemical called juglone that inhibits the growth of many plants. Composting does not break down juglone, so it will remain in your finished compost and stunt or kill sensitive plants you are trying to grow. Oak leaves are safe; black walnut is not.

Ash, Sawdust, and Wood Products

Charcoal ash from a grill or fireplace should not go in compost. It contains residue from lighter fluid or other accelerants and can alter the pH of your pile. Wood ash from a fireplace burning untreated wood is acceptable in small amounts — a light dusting — but too much raises pH and can burn plant roots.

Sawdust from treated wood, plywood, or particle board contains glues and preservatives. Sawdust from untreated hardwood is safe but should be mixed in sparingly because it breaks down slowly and can compact your pile. Sawdust from pressure-treated lumber or MDF should go to the trash.

Glossy, Coated, and Printed Paper

Magazine pages, newspaper inserts printed in color, and takeout containers with plastic or wax coating will not decompose. The coating prevents moisture from reaching the paper fibers, so they sit in your pile unchanged. Receipts, which are often printed on thermal paper coated with BPA, also belong in the trash.

Plain newsprint and uncoated cardboard (the inside of a cereal box, a plain shipping box) are safe. Shredded office paper is safe if it is not glossy. When in doubt, check the back of the paper — if it feels slick or plastic-like, it is coated and should not go in compost.

Oils, Fats, and Prepared Foods

Cooking oil, butter, lard, and salad dressing should go down the drain (in small amounts, cooled) or in the trash. These fats coat particles in your compost pile and prevent air from reaching the center, which slows decomposition and creates anaerobic conditions that smell terrible. They also attract rodents and raccoons.

Prepared foods — pasta, rice, bread, baked goods, sauces — break down slowly and attract pests. Leftovers with meat, dairy, or oil are especially problematic. Vegetable scraps and fruit peels are safe; prepared dishes are not.

Frequently Asked Questions

Can I compost paper towels or napkins?

Yes, if they are plain and unbleached. Bleached white paper towels are safe in small amounts, but they break down slowly. Napkins with food residue are fine as long as the food is plant-based — no meat, dairy, or oil. Paper towels with synthetic fibers or plastic coating should not be composted.

What about coffee filters and tea bags?

Coffee filters are safe and break down quickly. Most tea bags are safe, but check the label — some contain plastic fibers or synthetic materials. If the bag feels plasticky or does not tear easily when wet, remove the tea leaves and compost only those, leaving the bag in the trash.

Can I put citrus peels and onion skins in compost?

Yes. Citrus peels, onion skins, and garlic skins all compost safely. They break down slowly, so chop them into smaller pieces to speed decomposition. The myth that citrus attracts pests is false — the real culprits are meat, dairy, and oils.

Is it safe to compost grass clippings treated with herbicide?

No. Herbicide residue persists through composting and will damage or kill plants when you use the finished compost. If your lawn was treated, bag the clippings and throw them away for at least two mowing cycles after process, then check the product label for how long to wait before composting is safe.

Can I compost dryer lint?

Only if it is from natural fibers like cotton or wool. Lint from synthetic fabrics (polyester, acrylic, nylon) will not break down. If you cannot confirm the fiber content of your clothes, assume the lint contains synthetics and throw it away.