Compost is a recipe for regeneration.

Compost returns organic matter and nutrients to our soils, instead filling our landfills. When food scraps, yard debris and other compostable materials sit in the landfill, useless and unable to break down, they produce methane – a powerful greenhouse gas that contributes to global climate change.

Food scraps turning into soil supporting a small plant.

On the other hand, compost gives organic matter a new life, turning our carrot tops and coffee grounds into a nutrient-rich material that nourishes our gardens, farms and natural communities. Compost helps our soils absorb and hold more water, prevents erosion and protects against soil-borne plant diseases. It also acts a carbon bank – removing and storing carbon dioxide, the most common greenhouse gas emission, from our atmosphere.

Want to learn more? Read Compost: A Multi-layered Solution.

In our continued celebration of soil, we bring you tips to make Boulder’s compost the best it can be.

Compost Quality Matters

It is important that we work together to create high quality compost free from plastics, metals and other materials that belong elsewhere. When added to your compost bin, these pollutants have the potential to make their way into our soils and waterways.

Help us keep our community’s curbside compost healthy and free of contamination.

  • Sort correctly. Learn what goes in your curbside compost bin, and think before you throw.

    Some paper products – coffee cups, plates and ice cream containers – are coated with a thin layer of plastic film. These products belong in the trash. When in doubt, give Eco-Cycle a shout or consult their A-Z Recycling Guide.
Red onion with produce sticker on it.

Be sure to remove produce stickers from fruits and vegetables before putting them in your curbside or backyard compost bin.

  • Avoid microplastic contamination.

    When broken down in the composting process, plastic film creates microplastics, tiny plastic particles that pollute our soils, waterways, wildlife and bodies. Like any plastic, microplastics do not decompose. Thus, they negatively affect our environment indefinitely.

    • Recycle milk and juice cartons in your single-stream recycling bin.
    • Choose reusable containers instead of plastic-coated paper products. Use reusable takeout containers whenever possible.
    • Remove stickers from fruit and vegetable scraps.
    • Throw plastic-coated paper plates, cups and takeout boxes in the trash.
    • Buy certified compostable products when you need something disposable.
  • Look for Biodegradable Products Institute (BPI) certification.

    There is only one reliable way to make sure a product is truly compostable and safe for our soils: look for BPI certification.

BPI Compostable Logo

Look for the BPI Certified Compostable logo.

Be on the lookout for non-compostable look-alikes labeled with potentially misleading words like:

  • Eco-friendly
  • Biodegradable
  • Green
  • Plant-based

Surprisingly, none of these phrases mean a product can be composted. These products may contain harmful chemicals and plastics that contaminate our soil. Check out Eco-Cycle's Is It Compostable? guide for a longer list of non-compostable materials.

These labels also mean certified compostable: ASTM D6400, ASTM D6868, ingeo, NatureWorks LLC and PLA 7

Four things you may not know you can compost in your curbside bin.

  • Low grade paper like tissues, paper towels and wax paper
    • Make sure wax paper is not coated with a plastic film. Not sure if your waxy paper is compostable? Scrape the waxy surface with a butter knife or fingernail. Compostable wax paper will show a line, while plastic-coated paper will not.
  • Dark and brightly colored paper
  • Meat and dairy
  • Greasy pizza boxes and other cardboard containers
    • Make sure cardboard is not covered in plastic film, and remove any stickers or tape.
Empty greasy pizza box.

Greasy pizza boxes should be put in your curbside compost bin.

Three things you cannot compost in your curbside bin.

  • Pet waste
  • Freezer cartons and containers
    • These cannot be recycled either! They go in the trash.
  • Plastic bags

Rule of thumb: do not compost materials and products that have never been alive and are not labeled with a BPI or other certified compostable logo.

Three non-compostable coffee cups.

These coffee cups are lined with a thin plastic coating and do not have a certified compostable label, so they must be thrown in the trash. The single-use plastic lids belong in the trash too.

More On Compost Sorting

Just starting to learn how to sort? Check out the city’s Zero Waste Sorting Quiz for an interactive and educational game.

Already a sorting expert? Test your knowledge with Eco-Cycle's sorting game for hard-to-recycle and hazardous materials.