You should never put in a compost bin these three things: pet waste, treated wood, and synthetic materials. Pet waste carries pathogens your bin can't kill. Treated wood puts toxic chemicals into your compost. Plastics and synthetics never break down no matter how long they sit in the pile.
I tossed used cat litter into my bin during my first year of composting. It seemed logical since cat waste is organic matter. Three months later I couldn't trust that batch on my vegetable beds. Cat feces carry Toxoplasma and other parasites that home compost temps don't destroy. I also threw in glossy magazine pages once thinking paper is paper. Those shiny pages sat unchanged for over a year. The inks left chemical residue mixed right into the finished compost.
Here is your complete compost bin no list. Keep every one of these items out of your bin for safe, clean compost.
Pet Waste and Litter
- Health risk: Dog and cat feces contain harmful bacteria and parasites like E. coli, Salmonella, and Toxoplasma that survive normal composting temperatures.
- Why it matters: Home compost piles rarely sustain the 130-150°F internal temperatures needed for long enough to destroy these pathogens safely.
- Safe alternative: Bag pet waste separately for trash pickup or look into dedicated pet waste composters that keep it isolated from garden compost.
Treated Wood and Charcoal
- Chemical danger: Pressure-treated lumber contains copper, arsenic, or chromium compounds that leach into compost and contaminate your soil for years.
- Coal and charcoal ash: These contain sulfur compounds and heavy metals that harm soil microbes and can make your compost toxic to plants.
- Safe alternative: Use only untreated, unpainted wood scraps, sawdust from clean lumber, and wood ash from natural hardwood fires in small amounts.
Synthetic and Plastic Materials
- Breakdown problem: Plastics, synthetic fabrics, and rubber never decompose in a compost bin and leave behind microplastic contamination in your soil.
- Hidden plastics: Tea bags, produce stickers, and so-called compostable packaging often contain plastic liners that don't break down in home bins.
- Safe alternative: Remove all stickers from fruit scraps, open tea bags to dump loose leaves, and only add certified home-compostable items.
Diseased Plants and Weeds
- Spread risk: Plants with fungal diseases like blight or powdery mildew can survive composting and reinfect your garden when you spread the finished material.
- Weed seeds: Aggressive weeds that have gone to seed may survive unless your pile hits 140°F or higher for several days in a row.
- Safe alternative: Bag diseased plants for municipal yard waste programs that use industrial hot composting to destroy pathogens and weed seeds.
Chemically Treated Yard Waste
- Herbicide danger: Lawn clippings treated with broadleaf herbicides can persist through composting and kill your garden plants when you apply the finished compost.
- Persistence: Some herbicides like aminopyralid stay active in compost for over two years and damage tomatoes, beans, and other sensitive crops.
- Safe alternative: Only compost grass clippings from lawns you know haven't been sprayed, and wait at least three mowings after any chemical application.
The EPA items to avoid composting list also flags coal ash, dairy, meat, and sprayed yard waste. Beginners toss these in all the time without a second thought. You end up with bad compost or a bin crawling with flies and rodents.
You have good options for scraps your home bin can't handle. City composting programs take meat, dairy, and bones at plants that hit 160°F for days on end. A bokashi system ferments meat and dairy in a sealed bucket with helpful microbes. You then bury the output in soil where it breaks down fast. I started using bokashi last year for my kitchen meat scraps and it works great alongside my outdoor bin. These two methods let you keep more waste out of the landfill without risking your garden compost.
Read the full article: 8 Best Compost Bins for Every Garden
