Is That Really Compostable?

Composting is a great way to save food scraps from ending up in a landfill. But some items labeled "compostable" won't break down in your backyard.

Generating less trash is a worthy goal. But we all have to eat, and more food ends up in landfills than any other type of trash material, according to the Environmental Protection Agency. It makes up almost one-fourth of landfilled trash.

Composting is an excellent way to cut back on this and turn organic waste—including food scraps, eggshells, coffee grounds, and yard trimmings—into compost, a useful product that can be added to soil to improve plant growth in your garden or yard. And more and more disposable cutlery, cups, packaging, and other products also come with a "compostable" label.

But knowing what exactly you can put into a compost bin can be complicated. And the stakes are high: If you put in items that won't break down, they’ll just sit there, adding to a litter problem.

To help you figure out what you can and can't compost, Consumer Reports consulted with waste management, composting, and agricultural experts. With a little care you can efficiently cut back on your organic trash production without creating any icky smells or having to deal with rotten food, says Rhonda Sherman, an extension specialist in the department of horticultural science at NC State University and the founder and director of NC State's Compost Learning Lab.

Before trying to figure out what you can and can't compost, it's important to understand that there are a variety of composting systems out there, ranging from backyard barrels and worm bins to farm systems to large-scale commercial or municipal facilities. What's allowed in compost varies considerably depending on the system you’re using.

Composting itself refers to the process by which organic waste can be broken down into compost—a soil-like material—using microbial activity. To create the right conditions for this activity, you need the proper mass, moisture level, and mix of carbon and nitrogen. That means food waste scraps need to be mixed with enough carbon-rich material, like leaves or straw or wood shavings, says Jean Bonhotal, director of the Cornell Waste Management Institute. Under the right conditions, the pile will heat up as the microbes break down organic material into compost.

Large-scale systems—like the one you might use if your city collects food scraps or if you pay a service that picks up organic waste—are regulated by states and have to meet or exceed certain safety standards, according to Sherman. Because these systems are professionally managed and heat up to high temperatures, they’re generally able to break down items you couldn't put into a typical home compost pile. These systems reach temperatures that will kill dangerous pathogens, which—in a simple backyard compost pile—might hang around and ultimately end up in soil.

Home compost piles aren't typically as strictly managed and monitored as large-scale systems, so their temperatures are rarely as high. That's why most experts advise home composters to avoid harder-to-break-down materials (see below), things that could smell and attract animals, and anything that could carry pathogens you don't want in your compost.

Vermicomposting, or breaking down organic waste using worms, is another way to dispose of your food scraps at home. A vermicomposting system is the most accessible for apartment dwellers because it's easiest to do indoors, Sherman says, where typical composting isn't possible. (Some apartment dwellers may have access to a pickup or dropoff compost system, too.) A small indoor vermicomposting system is slightly less flexible than a typical backyard composting system in terms of what it can handle. (See our guide to composting in an apartment.)

Read on for the details on what you can put into the compost depending on which compost system you use.

Backyard compost bin: Most food scraps are fine. But you should avoid bones, meat, fish, and milk products. And you should never put pet feces into a home compost system. Some of those items could contain pathogens you don't want in your compost, and some could attract animals to your pile.

To avoid any "ick factor," you can keep a collection bin for your food scraps in the freezer, Sherman says. That way, you avoid having them break down in a countertop bin. The smaller you dice your material, the more easily it will break down. Whenever you do dump your waste into your pile, cover it immediately with some leaves, straw, or similar material. "You should never see any food in your bin," Bonhotal says.

Vermicomposting: You can dispose of most of the same food scraps that you would in a backyard compost bin. But there are some additional exceptions. "Worms can be picky eaters; they’ll shy away from some things," Sherman says. They may avoid garlic, onions, and citrus peels, so it's best to avoid putting those items into a small vermicompost bin. (You can break down some of these items in larger vermicompost systems, where they’ll be more dispersed with other items.)

Large-scale composting systems: These can handle all the food scraps you can put into backyard compost, plus bones, meat, fish, cheese, and other milk products. They’re also able to neutralize pathogens found in pet feces, but don't toss any in without verifying whether or not your system accepts it. (An additional note of caution: If you pick up pet feces in a bag, there's a good chance that bag isn't compostable. See the next section for more on how to tell.) In general, it's always worth checking with your system's operator to see exactly which products they do and don't accept.

Backyard compost or vermicompost: Nonfood products labeled as compostable aren't likely to break down in your backyard pile or in a vermicompost system. Some—if they’re made from paper that's not lined with anything—may be compostable in small quantities in a backyard bin, Sherman says. Just make sure they’re cut up into small pieces, and plan to compost the occasional paper plate—not all of your food packaging.

Large-scale composting system: Sherman says she’d only consider packaging products (beyond uncoated paper) compostable if they have gone through the process of being certified as such by the Biodegradable Products Institute (BPI), a nonprofit group that ensures packaging meets certain requirements that make it compostable. Your system may use that standard or have another, but it's best to check first. Some facilities may not want utensils, for example, because these are harder to break down. And you shouldn't toss in a full stack of compostable cups or bowls, Bonhotal says. The items would need to be separated to break down.

Terms like biodegradable, bio-based, and made from plants "are not synonymous with ‘compostable,’" says Rhodes Yepsen, executive director of BPI. Biodegradable, for example, might refer to ’photodegradable’ products that contain an additive that needs sunlight to break it down. Sunlight won't penetrate your compost pile, however, Sherman says, and plastics with these additives are not actually compostable.

"Often products carrying these claims are designed to look like certified compostable products when in fact they are not," Yepsen says. "Contamination from ‘look-alike’ noncompostable products is one of the biggest challenges composters face."

States including California, Maryland, and Washington have all banned the use of the term "biodegradable" on packaging for that reason.

Composters should also be aware of PFAS—per- and poly-fluoroalkyl substances, which are sometimes added to packaging to make it grease- or water-resistant. These chemicals practically never break down naturally, which is why they’re sometimes referred to as forever chemicals.

Products certified as compostable by BPI should have no intentionally added PFAS. But a certain level of contamination with PFAS may still exist in some products that don't have intentionally added PFAS, as previous testing by CR has shown. That's because after decades of use, these chemicals are often found in recycled paper or even ink, for example.

It can be difficult to tell if packaging contains PFAS, so this may be another reason to avoid putting packaging into your home compost unless it has a BPI certification and you know it comes from a retailer committed to not using PFAS.

Kevin Loria

I'm a science journalist who writes about health for Consumer Reports. I'm interested in finding the ways that people can transform their health for the better and in calling out the systems, companies, and policies that expose patients to unnecessary harm. As a dad, I spend most of my free time trying to keep up with a toddler, but I also enjoy exploring the outdoors whenever possible. Follow me on Twitter (@kevloria).