Items That Will Ruin Your Compost or Attract Pests

Meat, fish, dairy, oils, and fats break down slowly and create odor problems that draw rats and raccoons to your bin. Diseased plants and weeds with seeds will survive the composting process and spread problems to your garden. Pet waste from dogs and cats can carry parasites that survive low-temperature compost and contaminate soil where you grow food. Glossy or coated paper, treated wood, and synthetic materials do not decompose and will remain as trash in your finished compost.

The items you exclude matter as much as what you add. A single batch of meat scraps or a handful of glossy magazine pages can compromise months of work. The goal is material that breaks down into usable soil amendment, not a pile that attracts vermin or leaves behind plastic and chemicals.

Key Takeaways

  • Meat, fish, dairy, oils, and fats create odor and attract rodents; they belong in the trash or a separate animal-waste system.
  • Diseased plants, weeds with mature seeds, and invasive species will survive composting and spread problems to your garden soil.
  • Pet waste from dogs and cats carries parasites that survive home compost temperatures and should never go in bins used for food gardens.
  • Glossy paper, treated wood, synthetic materials, and coal or charcoal ash do not break down and will remain as contaminants in finished compost.
  • Sawdust from treated or pressure-treated wood releases toxins; use only untreated wood sawdust in small amounts.

Meat, Fish, Dairy, and Oils That Attract Rodents

Meat scraps, fish bones, shellfish shells, cheese, milk, butter, and cooking oils should never go in a home compost bin. These materials decompose slowly and create strong odors that attract rats, raccoons, opossums, and other pests to dig into your pile. Once rodents find your bin, they will return repeatedly and may move into nearby structures.

Even small amounts cause problems. A single chicken bone or a spoonful of leftover gravy is enough to draw attention. If you want to compost animal products, you need a separate enclosed system designed for hot composting or a commercial facility that reaches temperatures above 140°F — temperatures most home bins never reach. Your regular compost bin should stay meat-free.

Diseased Plants and Weeds With Seeds

Plants infected with fungal diseases, bacterial wilts, or pest infestations should go in the trash, not the compost. Compost piles rarely reach temperatures high enough to kill disease spores. When you spread that compost in your garden, you are spreading the disease to healthy plants. The same applies to weeds that have already gone to seed — the seeds survive composting and germinate in your garden beds.

Invasive plants like bindweed, bermuda grass, and morning glory roots can regrow from fragments in compost. If you are unsure whether a plant is diseased or seeded, throw it away. The cost of a trash bag is far less than the cost of replanting a garden bed or treating a fungal outbreak that spreads through your soil.

Pet Waste and Animal Manure That Carries Parasites

Dog and cat feces contain parasites and pathogens that survive home composting temperatures. These include roundworms, hookworms, and E. coli bacteria that can contaminate vegetables and cause serious illness. Never add pet waste to a compost bin you plan to use on food gardens. This applies to litter box waste, dog waste, and any bedding soiled with pet feces.

Herbivore manure from horses, chickens, rabbits, and goats is safe in small amounts if the animals have not been treated with antiparasitic drugs recently. Cow manure is generally safe but should be aged or hot-composted. Pig manure carries more risk and is best avoided. If you are unsure about the source or health history of any manure, leave it out.

Glossy Paper, Treated Wood, and Synthetic Materials

Glossy magazines, coated cardboard, and shiny paper do not break down in a home compost pile. The coating is designed to resist moisture and decay. When you spread finished compost, these fragments remain as trash in your garden beds. Newspaper and plain cardboard are fine; glossy paper is not.

Treated wood, pressure-treated lumber, and plywood release chemicals like copper and arsenic into compost as they slowly degrade. Sawdust from these materials is toxic. Use only untreated wood sawdust, and keep it to a small percentage of your pile. Synthetic materials — plastic, rubber, foam, synthetic fabrics — do not decompose and should never enter a compost bin.

Coal Ash, Charcoal Ash, and Treated Wood Ash

Wood ash from a fireplace or wood stove can be added in small amounts to balance acidic compost, but coal ash and charcoal ash contain substances that harm plants and soil. Do not use either. Ash from treated wood or painted wood contains heavy metals and should be thrown away.

Even untreated wood ash should make up no more than 5 to 10 percent of your compost by volume. Too much ash raises the pH too high and can lock up nutrients. If you have a large quantity of ash, spread it thinly on your lawn or garden rather than adding it to the bin.

Citrus Peels, Onions, and Garlic in Large Amounts

Small amounts of citrus peels, onion skins, and garlic are fine, but large quantities can slow decomposition and repel worms. Citrus oils are antimicrobial and can inhibit the microbes that break down compost. Onions and garlic contain compounds that deter earthworms. If you have a lot of these materials, spread them out over time rather than adding them all at once.

A few lemon peels or onion layers mixed into a large pile will not cause problems. But if you are composting a bulk harvest of citrus or a large quantity of onion waste, add it gradually over several weeks and monitor the pile's temperature and activity.

Frequently Asked Questions

Can I compost bread, pasta, and cooked grains?

Cooked food scraps like bread, pasta, rice, and beans can go in compost but attract rodents and insects just like meat does. If your bin is enclosed and you bury food scraps deep in the center of the pile, the risk is lower. In an open pile, skip them. Raw grains and flour are safer but still draw pests if exposed.

What about coffee grounds and tea bags?

Coffee grounds and loose tea leaves are excellent for compost. Tea bags are fine only if they are made of paper or plant fiber — many bags contain plastic or synthetic mesh that will not decompose. Remove the staple from paper tea bags before adding them. when ready tea bags are usually safe; check the packaging to be sure.

Can I compost sawdust from my workshop?

Sawdust from untreated wood is safe in small amounts mixed throughout the pile. Sawdust from pressure-treated lumber, plywood, MDF, or painted wood should never be composted. If you are unsure whether the wood was treated, do not use the sawdust. Treated wood releases arsenic and copper that will remain in your compost permanently.

Is it okay to add weeds if I pull them before they flower?

Weeds pulled before they set seed are generally safe to compost. However, some weeds like bindweed and bermuda grass spread from root fragments and rhizomes. If the weed has any underground runners or bulbs, throw it away instead. When in doubt, trash it — one missed weed can infest your entire garden.

What should I do with materials I cannot compost?

Meat, fish, dairy, diseased plants, pet waste, and treated materials belong in the trash. Some communities have separate food-waste collection programs that accept meat and dairy; check your local waste management options. Diseased plants should be bagged and thrown away, not left in a pile where spores can spread.