Most compostable bags break down only in industrial composting facilities, not in your backyard pile
A bag labeled "compostable" will not decompose in a home compost bin or landfill the way you might expect. Most compostable bags are made from plant-based plastics like polylactic acid (PLA) or polyhydroxyalkanoates (PHA), which require specific conditions to break down: temperatures between 130 and 180 degrees Fahrenheit, controlled moisture, and the right microbial environment. Your backyard compost rarely reaches those temperatures, so the bag will sit there for years.
Industrial composting facilities have the equipment and conditions to break down these materials in 90 to 180 days. If you send a compostable bag to a facility that accepts them, it will decompose. If you throw it in a landfill or your home compost, it will not—and it may contaminate a batch of finished compost if someone tries to use it there.
The label "compostable" is not the same as "biodegradable." Biodegradable means something will eventually break down in any environment. Compostable means it will break down in a specific composting environment, usually industrial. Read the fine print on the package to see which type of facility is required.
Key Takeaways
- Compostable bags need industrial composting conditions (high heat, moisture, and microbes) to break down, which home compost piles do not provide.
- Most compostable bags are made from plant-based plastics like PLA or PHA, not traditional petroleum plastic.
- If your area has an industrial composting program, check whether it accepts bags before you buy them—not all programs do.
- Bags labeled "home compostable" are rare but do exist; they break down in backyard conditions, though they cost more and are harder to find.
- Putting a compostable bag in a landfill or home compost pile wastes the material and does not reduce environmental harm compared to regular plastic.
How industrial composting breaks down these bags
Industrial composting facilities maintain temperatures of 130 to 180 degrees Fahrenheit by turning large piles of organic material and monitoring moisture. The heat, combined with bacteria and fungi already present in the compost, breaks down the plant-based polymers in compostable bags into carbon dioxide, water, and biomass. This process typically takes 90 to 180 days, depending on the facility and the material.
Your home compost pile, even if well-maintained, rarely exceeds 100 to 120 degrees Fahrenheit at its core. Without the sustained high temperature and the specific microbial community that industrial facilities cultivate, a compostable bag will remain largely intact. Some sources claim home compostable bags exist, but they are uncommon and cost significantly more than standard compostable bags.
What happens if you put a compostable bag in the wrong place
If you put a compostable bag in your home compost pile, it will sit there for years without breaking down. When you try to use the finished compost in a garden, you may find pieces of the bag mixed in, which can harm plants or make the compost unusable. Some gardeners have reported finding intact bags in compost piles years after adding them.
If you throw a compostable bag in a landfill, it will not decompose there either. Landfills are anaerobic (lacking oxygen), which slows decomposition of almost everything. A compostable bag in a landfill behaves like regular plastic—it persists for decades. The environmental benefit of choosing compostable over conventional plastic only exists if the bag reaches an industrial composting facility.
If you send a compostable bag to a recycling center that does not accept it, it can jam sorting equipment or contaminate batches of recycled plastic. Always check your local program's rules before putting any bag in the recycling bin.
How to learn about your area accepts compostable bags
Contact your local waste management department or visit their website to ask whether they operate or partner with an industrial composting facility. Some municipalities have their own facilities; others contract with regional ones. Ask specifically whether they accept bags made from PLA or PHA, because some facilities accept only loose food scraps and yard waste.
If your area does accept compostable bags, the facility will usually provide a list of approved materials and instructions for how to prepare them. Some programs ask you to place bags in a separate bin; others ask you to dump the contents into a compost cart and keep the bag out. Follow those instructions exactly, because a bag placed in the wrong stream can disrupt the entire batch.
If no industrial composting program exists in your area, compostable bags offer no environmental advantage over regular plastic bags. In that case, reusable bags or paper bags are better choices.
The difference between PLA, PHA, and other plant-based plastics
PLA (polylactic acid) is the most common compostable plastic. It is made from corn starch or sugarcane and is used in bags, food containers, and cutlery. PLA requires industrial composting and will not break down in home compost or landfills. It is also not accepted by most plastic recycling programs, so it often ends up in landfills anyway.
PHA (polyhydroxyalkanoates) are newer plant-based plastics that some manufacturers claim break down in home compost or even in soil and ocean water. However, these claims are not yet widely verified, and most PHA products still require industrial composting. Check the package to see what conditions the manufacturer specifies.
Starch-based plastics are blends of traditional plastic with cornstarch. They break down faster than pure plastic but usually still require industrial composting. They are sometimes labeled "degradable" rather than "compostable," which means they will eventually fragment into smaller pieces but may not fully decompose.
Reading the label: what the certifications mean
Look for third-party certifications on the package, which indicate the bag has been tested and verified to meet specific standards. The most common certifications are from the Biodegradable Products Institute (BPI) in North America and the European Bioplastics Association in Europe. A BPI certification means the bag will break down in an industrial composting facility within the timeframe specified.
If a bag is labeled "home compostable," it should carry a certification stating that it breaks down in home compost conditions. These bags are rare and cost more. If you see "home compostable" without a certification mark, treat it with skepticism—the claim may not have been tested.
Bags labeled only "biodegradable" or "eco-friendly" without a specific certification are vague and often misleading. These terms do not may provide the bag will break down in any particular environment. Always look for the specific facility type required: industrial compost, home compost, soil, or marine.
Alternatives if compostable bags are not an option in your area
If your area does not have industrial composting, consider reusable bags for groceries and storage. A cloth or sturdy plastic bag used dozens of times has a lower environmental impact than single-use bags, whether compostable or not. Reusable bags work for food scraps too—line a bin with one, empty it into your compost pile, and rinse it out.
Paper bags are another option. They break down in home compost piles within weeks and do not require special facilities. However, they are not waterproof, so they work better for dry materials like leaves and grass clippings than for wet food scraps.
If you do have access to industrial composting, compostable bags can be useful for collecting food scraps and keeping your compost bin clean. Just make sure you understand your program's rules and follow them exactly. Putting the wrong item in the wrong stream can undo the environmental benefit for the entire batch.
Frequently Asked Questions
Can I compost a compostable bag in my backyard?
No, not unless the package specifically says "home compostable" with a certification mark. Most compostable bags require industrial composting temperatures of 130 to 180 degrees Fahrenheit, which home piles do not reach. The bag will remain in your pile for years and may contaminate your finished compost.
What should I do with compostable bags if I don't have access to industrial composting?
Treat them like regular plastic bags: reuse them or throw them in the trash. Putting them in a landfill is not ideal, but it is better than putting them in home compost where they will not break down. If you want to reduce waste, switch to reusable bags or paper bags instead.
Are compostable bags better for the environment than regular plastic?
Only if they reach an industrial composting facility. If they end up in a landfill or home compost, they persist like regular plastic and offer no environmental advantage. The benefit depends entirely on your local waste system, not on the bag itself.
Can I put a compostable bag in my recycling bin?
No. Compostable bags are not accepted by most plastic recycling programs and can jam sorting equipment. Check your local program's rules, but the answer is almost always no. If you cannot compost it industrially, throw it in the trash.
Why do compostable bags cost more than regular plastic bags?
Plant-based plastics like PLA and PHA are more expensive to produce than petroleum-based plastic. The higher cost reflects the material itself, not a may provide that the bag is better for the environment. You are paying for the material, not for a solution—the solution depends on whether your area has industrial composting.