Is Compostable Plastic Really Compostable + 3 Ways to Break It Down

Plants growing in compostable plastic cups

The global plastic pollution problem is not something new. This once beholden miracle substance has found its way to every corner of the world through the various forms plastic waste can take. Being positioned at the forefront of environmental discussions, scientists, politicians, and activists have dedicated time and energy to replacing or remediating this material. But is there another option beyond recycling plastic? Yes, and that answer is compostable plastic.

New plastics have recently begun to enter the market, touting the ability to be composted and biodegraded, further diverting plastic from the waste stream. But is this biodegradable plastic actually what they claim to be, or is this just another attempt at clever greenwashing? This article explores the topics of:

But before you click away to those frequented questions at the bottom of the page, let's begin with a dive into the topic of what are compostable plastics?

What is compostable plastic?

Close up of a compostable plastic cup

Compostable plastic is a plant-based plastic manufactured and designed to break down into natural substances through the composting process. The decomposition yields carbon dioxide, water, and soil conditioning material without leaving any toxic residue.

According to a European Bioplastics e.V. 2020 report, of the current plastic products on the market, only around 1% of them can be considered compostable. These plastics are manufactured from plant-based materials and designed to look and feel like traditional fossil-fuel plastics. But don't be fooled, as placing these plastics back into the recycling stream can disrupt the process.

Various organizations are setting the standard on how we label items as compostable. One example is that of The American Society for Testing and Materials (ASTM) International. This group has defined compostable plastic as "a plastic that undergoes degradation by biological processes during composting to yield carbon dioxide (CO2), water, inorganic compounds, and biomass at a rate consistent with other known compostable materials and that leaves no visible, distinguishable, or toxic residue." This definition acts as a baseline to help differentiate between traditional, compostable, and biodegradable plastics. 

Here are just a few of the groups that are setting the standards for compostable plastics:

  • American Society for Testing and Materials (ASTM) International
  • European Committee for Standardization (CEN)
  • International Organization for Standardization (ISO)
  • TUV Austria Begium NV
  • Biodegradable Products Institute (BPI)

Thanks to these companies, a better understanding of compostable plastics is becoming a regular part of the plastic industry. But even though these companies have defined them as such, are these plastics compostable?



So, is compostable plastic really compostable?

Compostable plastic bag in a compost bin

Yes, compostable plastic is really compostable. But that doesn't mean it's approved to go into your backyard compost bin beside your food waste. Compostable plastics require specific composting conditions to guarantee it breaks down; conditions achieved at industrial composting facilities.

The wonder of composting comes from a specific biodegradation process known as decomposition. In this process, complex organic material will break down into simple organic and inorganic matter with the correct usage of heat, moisture, oxygen, particular microorganisms, and time. This means that the result of the decomposed (or composted) product becomes a soil conditioning material and inorganic materials like carbon dioxide, water, sugars, and salts. But not all composting and compostable materials are the same!



The most significant factor in the composting environment is the heat generated. Composting, when done correctly, can sustain temperatures high enough to sterilize soil-borne pathogens, leftover seeds, and harmful soil bacteria. When conditions are incorrect, the temperature drops and the process slows. Industrially compostable plastics require a tailored composting environment with prolonged high heat to guarantee an efficient breakdown. In proper commercial composting facilities, the biodegradable and compostable plastics should take roughly two to six months to break down, a process at the same rate as composting organic materials.

Always check your plastic before you compost. Introducing non-compostable plastic into a compost pile or commercial composting location can disrupt the breakdown process. Similarly, adding petroleum-based plastic to a compost bin can cause problems. For example, as plastic products slowly break down, they release microplastics that enter the natural environment. A compost bin exposed to microplastics may adversely affect the beneficial insect life. Worms exposed to microplastics have shown signs of stunted growth and loss of weight, which can significantly impact the surrounding ecosystem. 

So if traditional plastics in the environment are harmful, how do we tell the difference between old fossil-fuel plastics and new compostable plastics before composting?

How to tell which plastics are compostable

Hand pulling out plastic bags

So how can you tell which plastics are for composting? Sorting errors happen, but putting the wrong plastic in the wrong bin can do more than reduce the quality of the recyclable plastics bale. Since compostable plastics don't behave like petroleum-based plastics, they can't withstand recycling. But with two easy tricks and a little research, anyone can be well on their way to separating compostable from recyclable plastics. 

The first step on the journey to recognizing compostable plastics is understanding the current Resin Indicator Code (RIC). Currently, compostable plastics fall under recycling group "No.7," a group of miscellaneous plastics. This group of Code 7 plastics includes not only the plastics made of polylactic acid (No.7/PLA), which may be approved compostable, but also acrylic, fiberglass, and nylon, which are not. So, when examining recently purchased plastic containers, the best place to begin is the recycling Mobius to see if your product is in the correct category.

Beyond learning your RICs, there is another label that will better guide you towards choosing the correct plastic bin. Typically located beside the recycling Mobius is a compostable label. We are used to seeing these labels appear on our cardboard products, so it may surprise us when we pick up a plastic product with similar signage. It is important to note that just because something reads as compostable does not mean it's for home composting and may require industrial composting.

Finally, suppose you're looking to reduce your household's environmental impact. It may be best to research which companies provide compostable plastic alternatives. For example, the Biodegradable Products Institute (BPI) allows you to search by product and company for approved compostable products. This capability enables you to find new plastics that would best suit your needs and shows just how many of these compostable plastics are already on the market today.

These are a few quick ways to tell which plastics are compostable. Here are a few examples of compostable plastics already on the market:



Three ways to compost compostable plastic

Now that we understand what compostable plastic is, the question arises: what are some ways to compost these plastics? Here are some of the ways to break this plastic down!

1. Lomi

Lomi sitting on a kitchen counter

The Lomi is a great way to start the composting journey in the convenience of your own home. Using the Lomi Approved mode, calibrated heat and moisture break down fragmented Lomi approved plastics. Both fun and fulfilling, using the Lomi at home is easy and leaves users with a sense of pride as they reduce their home's waste output.

It is essential to be sure only to add Lomi approved plastic products. These tested and approved products will break down when using the Lomi Approved mode. Be sure these plastics are cut down to an appropriate size and mixed among the other compostable materials in the Lomi.

Users should note that dirt harvested at the end of the Lomi Approved mode does not get directly added to plants. It does not have a balanced nutrient mixture conducive to plant growth. Instead, add this material to your green bin to be further broken down.

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2. Backyard Compost

Person emptying food scraps into compost bin

When you come across an approved home compostable plastic but not Lomi approved, your next best bet is your outdoor compost. Select plastic products have been approved for composting at home in Europe. These special compostable plastics biodegrade in conditions achievable in the average home compost, even at lower temperatures. However, in America, there is no set standard for backyard composting so these products are harder to find and hence, it is recommended to send your compostable plastics directly to industrial composting instead of adding them into your backyard compost.

Hot compost will always break down materials faster than cold compost when composting approved plastics in the backyard. Depending on the pile's overall size, a typical hot compost can reach a temperature between 130F (54C) and 140F (60C) for hours to days. The upper end of this thermophilic range is when you see the breakdown of bacteria, pathogens, and complex organic waste.

3. Industrial Composting

Tractor pushing compost into a pile

Sadly, not every plastic will be able to be composted at home. Most compostable plastics are breakdown process in an industrial composting location. While the ability to reach thermophilic conditions in a home compost bin is possible, industrial composting facilities can easily obtain higher temperatures and maintain 140F (60C) temperatures for days at a time.

Commercial composting facilities can achieve ideal conditions for large-scale composting over extended periods. This capability makes them a perfect option for composting all remaining plastics that will not decompose at home. But, since compostable plastics are still a relatively new product, not every city can process these plastics. Remember to reach out to your local municipality or recycling facilities to see if the ability to compost plastic industrially is available in your area.

Five FAQs about compostable plastic

Compostable plastics have changed how we view the world of plastics, but with every new thing, there are always questions. Here are five common questions asked as people begin to explore this trend.

1. Are compostable and biodegradable the same thing?

Stacked biodegradable and compostable cups

No. When something is compostable, it requires human intervention in constructing a balanced compost pile that the material can compost in. When we hear that biodegradable plastic can break down, it means that microorganisms can break them down in a natural environment in a tailored time frame.

In the home compost, at-home compostable plastic will break down with the proper inputs of heat, moisture, soil microbes, and an appropriate carbon-to-nitrogen ratio. But the biodegradable plastics engineered to break down in soil or water may not break down in a compost bin. These products require different conditions to break down, which can be challenging to standardize due to the variability of soil and water conditions, especially in marine environments.

2. Will compostable plastics break down in a landfill?

Yes, but the breakdown of compostable plastics in a landfill is a prolonged process. In the incorrect conditions of the landfill—devoid of proper heat, moisture, and microbiome—compostable plastics can still take years or decades to break down.

But before throwing out compostable plastics, it is crucial to see if your local municipality can compost them. If composting is not available near you, recyclable bioplastic may be better than buying compostable plastics and disposing of the waste in a landfill.

Do not send compostable plastics to your local recycling unless otherwise stated. The intermixing of these with traditional plastic can cause issues in the recycling stream.

3. How long does compostable plastic take to break down?

Close up of plastic bottle on the forest floor

For a plastic to be compostable, it must decompose at the same rate as other organic materials. Most of the product should be broken down within six months, leaving no toxic material behind to affect plant growth adversely.

This time frame can be challenging to guarantee anywhere beyond a commercial composting facility. Even plastic products approved for at-home composting vary depending on the quality of the composting conditions. Biodegradable plastics engineered for commercial composting will not break down in a home compost and require an appropriate facility.

4. Can you put compostable plastic in your home compost pile?

No. Unless otherwise labeled as approved for home composting, it is not advised to compost these plastics at home and instead send them to an industrial composting facility. These commercial locations can produce optimal conditions for composting plastics that home compost bins cannot.

Suppose you are interested in composting at home. In that case, select European products carry labeling on compostable plastic items (like plastic bags) that approves the product for at-home composting. While American company BPI does have a similar certification process, there is currently no official at-home composting standard in North America. Lomi has also listed Lomi approved bioplastics that quickly break down without you having to leave the comfort of your home. But, a backyard bin may be your best bet for all other at-home compostables.

5. What plastics can Lomi compost?

Top down view of a lomi filled with food waste and plastic

Your Lomi electric composter can break down a variety of Lomi approved plastics. Lomi can compost the Repurpose brand compostable kitchen and bin bags as well as their assorted compostable utensil and spoons. Similarly, Eco-Products also has a selection of containers and cups that can go into your Lomi!

Lomi approved plastics have undergone rigorous testing and proved to break down efficiently. Explore the complete list of the Lomi approved products in our FAQ. Also, the packaging that Lomi ships in is compostable and can be completely broken down by Lomi! 

As more compostable plastics enter the market and standardizations become commonplace, the ability to compost locally will become easier. But until then, if your local composting facility cannot process compostable plastics, it may be up to you to reach out and ask the question, 'why hasn't this been done yet?' Together we can reduce plastic waste and promote a more earth-positive lifestyle.

If you are also looking to minimize waste around home, this article offers some other technologies that can help you reduce waste.

Written by: Tanner Sagouspe