Yes, you can compost cardboard, but it needs preparation

Cardboard breaks down in a compost pile, but not the way you might think. It does not disappear quickly like food scraps—it takes months or even a year depending on how you prepare it and what conditions your pile has. The key is shredding or tearing it into small pieces, keeping it moist, and mixing it with nitrogen-rich materials like grass clippings or food waste. Cardboard that is glossy, printed with colored inks, or coated with plastic or wax should stay out of your compost.

Plain cardboard—the kind used for shipping boxes, paper towels, and egg cartons—is made from plant fiber and will eventually become part of your finished compost. But cardboard is high in carbon, which means it needs to be balanced with materials that are high in nitrogen. A pile that is mostly cardboard will decompose very slowly and may start to smell or attract pests because it is not breaking down fast enough.

Key Takeaways

  • Tear or shred cardboard into pieces smaller than 2 inches across so it breaks down faster than whole sheets or boxes.
  • Remove all tape, stickers, plastic windows, and foam packing materials before adding cardboard to your pile.
  • Mix shredded cardboard with nitrogen-rich materials like grass clippings, vegetable scraps, or coffee grounds at a ratio of roughly one part cardboard to two parts nitrogen materials.
  • Keep the cardboard damp—it should feel like a wrung-out sponge—because dry cardboard will not decompose.
  • Avoid cardboard that is glossy, waxed, or printed with heavy colored inks, as these coatings do not break down in a home compost pile.

Prepare cardboard before it goes into the pile

Start by removing everything that is not cardboard. Peel off tape, stickers, plastic windows, foam packing peanuts, and any plastic or foam padding. These materials will not compost and will end up in your finished compost as trash. If the cardboard has a plastic coating on the inside (common in takeout boxes or produce boxes), that layer will not break down either—compost that box only if you can separate the plastic lining.

Tear or shred the cardboard into pieces. Whole sheets or flattened boxes will take a very long time to decompose because water and microbes cannot reach the inside of the material. Aim for pieces smaller than 2 inches across. You can tear by hand, cut with scissors or a utility knife, or run it through a paper shredder if you have one. Smaller pieces mean faster decomposition—sometimes a difference of several months.

Wet the cardboard before adding it to your pile. Dry cardboard will repel water and sit in your pile without breaking down. Soak it in a bucket or spray it with a hose until it is damp all the way through, then add it to your compost.

Balance cardboard with nitrogen-rich materials

Cardboard is a carbon-rich material, which means it needs to be mixed with nitrogen-rich materials to decompose at a reasonable speed. Nitrogen-rich materials include grass clippings, vegetable scraps, fruit waste, coffee grounds, crushed eggshells, and plant trimmings. A good starting ratio is roughly one part shredded cardboard to two parts nitrogen materials by volume.

If you add too much cardboard at once, your pile will slow down or stop decomposing. You will notice it taking on a sour smell or attracting flies and other pests—signs that the pile is not breaking down and is starting to rot instead of compost. If this happens, add more nitrogen-rich materials and turn the pile to mix everything together.

Layer the cardboard with other materials rather than dumping it all in one spot. Alternate a layer of shredded cardboard with a layer of grass clippings or food scraps. This mixing helps water and air reach all parts of the pile and speeds up decomposition.

Watch for moisture and turn the pile regularly

Cardboard needs to stay moist to break down. Squeeze a handful of compost from your pile—it should feel like a wrung-out sponge, with a few drops of water coming out if you squeeze hard. If it is dry, water it. If it is soggy and smells sour, turn the pile and add dry materials like shredded leaves or straw to absorb excess moisture.

Turning the pile every week or two speeds up decomposition of cardboard significantly. Each time you turn, you are breaking up the cardboard further, exposing new surfaces to microbes, and mixing in oxygen. A pile that is turned regularly will break down cardboard in 2 to 4 months. A pile that is left alone may take 6 months to a year.

Cardboard to avoid in your compost

Glossy or shiny cardboard does not belong in your pile. This includes magazine covers, some takeout boxes, and boxes with a plastic or wax coating on the inside. The coating prevents water from reaching the cardboard fibers, so it will not break down. It will sit in your finished compost as fragments.

Heavily printed cardboard with colored inks can go in, but plain or lightly printed cardboard is better. The inks used on most modern cardboard are soy-based or water-based and will break down, but there is no reason to add extra material if you have plain cardboard available. Cardboard printed with metallic inks or heavy dyes should be avoided.

Waxed cardboard—used for some frozen food boxes and produce boxes—will not compost. The wax coating is designed to repel water, which is exactly what stops it from breaking down. Cardboard with a plastic window (like a bakery box) should have the window removed before composting, or skip it entirely if the plastic is glued on too firmly to remove cleanly.

Using finished compost that contains cardboard pieces

Even after months of composting, small pieces of cardboard may still be visible in your finished compost. This is normal and not a problem. These fragments will continue to break down slowly once they are in your garden soil, and they will not harm plants. If you want a finer finished compost, sift it through a screen or hardware cloth before using it, and return the larger cardboard pieces to a new pile to finish breaking down.

Cardboard in finished compost actually helps with soil structure. As it continues to decompose in the soil, it improves water retention and creates space for air and roots. Many gardeners intentionally add shredded cardboard to their garden beds as a mulch layer, where it breaks down over time and feeds the soil.

Frequently Asked Questions

Can I compost cardboard with printing and colored ink?

Yes. Most modern cardboard printing uses soy-based or water-based inks that break down in compost. Lightly printed cardboard is fine to compost. Avoid cardboard with heavy metallic inks or dyes, but standard black or colored printing is not a problem.

How long does it take cardboard to compost?

Shredded cardboard mixed with nitrogen-rich materials and turned regularly will compost in 2 to 4 months. Whole sheets or cardboard in a pile that is not turned may take 6 months to a year. The smaller the pieces and the more often you turn, the faster it breaks down.

What if I have a lot of cardboard boxes?

Shred or tear them into small pieces and add them gradually over several weeks rather than all at once. Mix each batch with plenty of grass clippings, food scraps, or other nitrogen materials. Adding too much cardboard at one time will slow your entire pile.

Can I compost cardboard egg cartons?

Yes. Egg cartons are plain cardboard and will compost. Tear them into pieces, wet them, and mix with nitrogen materials. They break down faster than shipping boxes because they are thinner.

Should I remove the tape from cardboard boxes before composting?

Yes. Tape does not compost and will end up as plastic fragments in your finished compost. Peel off all tape, stickers, and plastic windows before adding cardboard to your pile.