Composting is an eco-friendly way to recycle organic waste, turning kitchen scraps and yard debris into nutrient-rich soil amendments. It reduces landfill waste, lowers greenhouse gas emissions, and enriches gardens. However, not everything belongs in a compost pile. Adding the wrong materials can attract pests, create foul odors, introduce pathogens, or even harm plants when the compost is used. This article explores what not to put in your compost, why these items are problematic, and how to dispose of them responsibly.
By understanding these composting pitfalls, you can maintain a healthy, efficient compost system that benefits both your garden and the environment.
Why Some Materials Don’t Belong in Compost
Composting relies on a delicate balance of carbon-rich “browns” (like dry leaves or cardboard), nitrogen-rich “greens” (like grass clippings or vegetable peels), air, and moisture. The process is driven by microorganisms that break down organic matter into humus. However, certain materials disrupt this balance, either by introducing harmful substances, slowing decomposition, or attracting unwanted critters. Others may seem compostable but pose risks to human health or the environment when the compost is applied to soil. Below, we categorize and explain the key items to avoid in your compost pile, offering practical alternatives for disposal.
1. Meat, Fish, and Bones
Why Avoid Them?
Meat, fish, and bones are organic, but they’re a poor fit for compost. These materials decompose slowly and release strong odors that attract pests like rats, raccoons, and flies. The anaerobic breakdown of animal proteins can also produce unpleasant smells, making your compost pile a neighborhood nuisance. Additionally, meat and bones may harbor pathogens like Salmonella or E. coli, which can survive in improperly managed compost and contaminate your garden soil.
Examples to Avoid:
- Raw or cooked meat (chicken, beef, pork, etc.)
- Fish and shellfish scraps
- Bones, cartilage, and fat trimmings
Disposal Alternatives:
- Municipal Food Waste Programs: Many cities offer curbside pickup for food waste, including meat and bones, which are processed at industrial composting facilities with higher temperatures to safely break down these materials.
- Home Freezing: If municipal pickup isn’t available, freeze meat scraps until trash collection day to reduce odors and pest attraction.
- Rendering: In some areas, rendering services collect animal byproducts for conversion into other products, though this is less common for household waste.
2. Dairy Products
Why Avoid Them?
Like meat, dairy products such as cheese, yogurt, milk, and butter attract pests and produce foul odors as they break down. Their high fat content slows decomposition, and they can foster anaerobic bacteria, leading to a slimy, smelly compost pile. Dairy can also introduce pathogens if not composted at high enough temperatures.
Examples to Avoid:
- Cheese rinds and scraps
- Sour cream or yogurt
- Butter or margarine
- Milk or cream
Disposal Alternatives:
- Municipal Composting: Check if your local waste program accepts dairy in food waste bins.
- Garbage Disposal: Small amounts of liquid dairy can go down the drain if you have a garbage disposal, but avoid large quantities to prevent plumbing issues.
- Trash: Seal dairy waste in compostable bags or containers and dispose of it in your regular trash to minimize odors.
3. Oily or Greasy Foods
Why Avoid Them?
Foods cooked in oil or grease, such as fried foods, salad dressings, or oily leftovers, can disrupt the compost’s microbial balance. Oils coat organic matter, reducing airflow and creating anaerobic conditions that slow decomposition and produce bad smells. They also attract pests and can make the compost pile too wet, leading to a sludgy mess.
Examples to Avoid:
- French fries or other fried foods
- Oil-soaked pizza boxes
- Salad dressings or mayonnaise
- Cooking oil or grease
Disposal Alternatives:
- Recycle Cooking Oil: Many recycling centers accept used cooking oil for conversion into biodiesel. Check local drop-off points.
- Municipal Food Waste: Some programs accept oily foods in food waste bins.
- Trash: Wrap greasy waste in newspaper or seal it in a container before tossing it in the garbage.
4. Pet and Human Waste
Why Avoid Them?
Feces from pets (dogs, cats, etc.) and humans can contain pathogens, parasites, and bacteria like Toxoplasma gondii or E. coli that may not be killed during home composting, which rarely reaches the high temperatures needed to sterilize waste. These pathogens can contaminate soil and pose health risks, especially in edible gardens. Pet waste may also contain medications or chemicals that persist in compost.
Examples to Avoid:
- Dog or cat feces
- Kitty litter (even if labeled “biodegradable”)
- Human waste from portable toilets or diapers
Disposal Alternatives:
- Pet Waste Systems: Use pet waste digesters (like the Doggie Dooley) for dog feces, which break it down safely underground.
- Trash: Bag pet or human waste securely and dispose of it in the trash.
- Specialized Composting: Human waste can be composted in highly controlled systems like composting toilets, but these require specific equipment and expertise.
5. Diseased Plants and Weeds
Why Avoid Them?
Plants infected with diseases or pests, such as blight, powdery mildew, or aphids, can spread those issues to your compost and, ultimately, your garden. Similarly, weeds with mature seeds or aggressive root systems (like dandelions or bindweed) may survive composting and sprout when you apply the finished compost. Home compost piles often don’t reach the sustained high temperatures (above 140°F) needed to kill pathogens or weed seeds.
Examples to Avoid:
- Tomato plants with blight
- Leaves with powdery mildew
- Weeds with seeds or invasive roots
- Pest-infested plant material
Disposal Alternatives:
- Burning: If permitted in your area, burn diseased plants or weeds to destroy pathogens and seeds (check local regulations).
- Municipal Yard Waste: Some municipal programs accept diseased plants for industrial composting or disposal.
- Trash: Bag and discard heavily diseased or weedy material in the trash to prevent spreading.
6. Treated Wood and Sawdust
Why Avoid Them?
Wood or sawdust from pressure-treated lumber, painted wood, or stained wood contains chemicals like arsenic, creosote, or heavy metals that can leach into your compost and soil, harming plants and potentially contaminating edible crops. Even small amounts of treated wood can make your compost toxic.
Examples to Avoid:
- Sawdust from treated lumber
- Painted or stained wood scraps
- Plywood or particleboard (contains adhesives)
Disposal Alternatives:
- Hazardous Waste Facilities: Treated wood should be taken to a hazardous waste drop-off site.
- Landfill: Check with your local landfill for guidelines on disposing of treated wood.
- Untreated Wood: If using wood in compost, ensure it’s untreated, natural wood, and use it sparingly as it decomposes slowly.
7. Non-Biodegradable Materials
Why Avoid Them?
Non-biodegradable items like plastics, metals, and synthetic materials don’t break down in compost and can contaminate the final product. Even some items labeled “compostable” or “biodegradable” (like certain plastics) require industrial composting facilities to decompose properly, not a backyard pile.
Examples to Avoid:
- Plastic bags, wrappers, or containers
- Foil, cans, or bottle caps
- “Biodegradable” plastics not certified for home composting
- Synthetic fabrics or rubber
Disposal Alternatives:
- Recycling: Sort plastics, metals, and glass for curbside recycling or drop-off centers.
- Trash: Dispose of non-recyclable, non-biodegradable items in the trash.
- Certified Compostable Products: Use only products certified for home composting (e.g., BPI-certified bags) and follow their guidelines.
8. Coal Ash and Charcoal
Why Avoid Them?
Coal ash and charcoal (especially from briquettes) contain chemicals like sulfur, boron, or heavy metals that can harm plants and alter soil pH. Charcoal briquettes often have additives like lighter fluid, which can contaminate compost. Wood ash from untreated wood is safe in small amounts, but coal ash and briquettes are not.
Examples to Avoid:
- Coal ash from fireplaces or grills
- Charcoal briquettes
- Ash with chemical additives
Disposal Alternatives:
- Trash: Dispose of coal ash and charcoal in the trash, sealed in a bag to prevent dust.
- Hazardous Waste: If the ash contains chemical residues, take it to a hazardous waste facility.
- Wood Ash: If using ash, ensure it’s from untreated wood and add it sparingly to avoid over-alkalizing the compost.
9. Certain Chemicals and Pesticides
Why Avoid Them?
Herbicides, pesticides, and other chemicals can kill the beneficial microorganisms in your compost pile, halting decomposition. Some persistent herbicides, like those containing clopyralid or aminopyralid, can remain active in compost and damage plants when the compost is used. Chemically treated grass clippings or plants are particularly risky.
Examples to Avoid:
- Grass clippings treated with herbicides
- Plants sprayed with pesticides
- Chemical fertilizers or cleaners
Disposal Alternatives:
- Avoid Chemical Use: Opt for organic gardening practices to minimize chemical residues.
- Trash: Dispose of chemically treated plant material in the trash.
- Wait It Out: Let treated grass clippings sit for several weeks before composting, if the herbicide is known to break down quickly (check product labels).
10. Glossy or Coated Paper
Why Avoid Them?
Glossy or coated papers, like magazines, stickers, or laminated sheets, contain plastics, chemicals, or heavy metals that don’t break down in compost and can contaminate the soil. While plain paper and cardboard are compostable, shiny or waxy coatings make these items unsuitable.
Examples to Avoid:
- Glossy magazines or catalogs
- Stickers or labels with adhesive
- Waxed or laminated paper
- Receipts (often coated with BPA)
Disposal Alternatives:
- Recycling: Most glossy paper can be recycled; check local guidelines.
- Trash: Dispose of coated or laminated paper in the trash.
- Plain Paper: Use only uncoated, non-glossy paper (like newspaper or cardboard) in compost.
Tips for Successful Composting
To avoid the pitfalls above and maintain a healthy compost pile, follow these best practices:
- Balance Materials: Aim for a 3:1 ratio of browns (carbon) to greens (nitrogen) for optimal decomposition.
- Turn Regularly: Aerate the pile every few weeks to promote airflow and prevent odors.
- Monitor Moisture: Keep the pile as damp as a wrung-out sponge—neither too wet nor too dry.
- Check Temperatures: Use a compost thermometer to ensure the pile reaches 130–160°F to kill pathogens and weed seeds.
- Screen the Final Product: Sift finished compost to remove any lingering non-compostable items.
Common Myths About Composting
Myth 1: “All Food Scraps Are Compostable”
While most fruit and vegetable scraps are great for compost, meat, dairy, and oily foods are not, as discussed above. Stick to plant-based scraps like peels, cores, and coffee grounds.
Myth 2: “Compostable Plastics Work in Backyard Piles”
Many “compostable” plastics require industrial facilities with high heat and specific conditions to break down. Always check if a product is certified for home composting.
Myth 3: “Compost Piles Don’t Need Maintenance”
Neglected piles can become smelly, pest-attracting messes. Regular turning, moisture checks, and proper material selection are key to success.
Environmental Impact of Proper Composting
By avoiding problematic materials, you ensure your compost is safe for your garden and the environment. Improper composting can lead to soil contamination, pest issues, or the spread of pathogens, undermining the benefits of composting. Proper composting, on the other hand, reduces landfill waste, lowers methane emissions, and creates a sustainable soil amendment that improves plant health and reduces the need for chemical fertilizers.
Conclusion
Composting is a powerful tool for sustainable living, but it requires care and knowledge to do it right. By avoiding meat, dairy, oily foods, pet waste, diseased plants, treated wood, non-biodegradable materials, coal ash, chemicals, and glossy paper, you can create high-quality compost that enriches your garden without risks. Always check local disposal options for items that don’t belong in your compost pile, and follow best practices to maintain a healthy, efficient system. With these precautions, your compost will be a boon to your soil and a step toward a greener planet.