Yes, you can compost cardboard, but only certain types break down well

Plain cardboard—the kind used for shipping boxes, paper towel tubes, and cereal boxes—decomposes in a compost pile or bin. Cardboard is made from plant fiber, so microorganisms and fungi can break it down over time. The catch is that cardboard takes longer to decompose than food scraps or grass clippings, and some cardboard has coatings or inks that should not go into your compost.

The cardboard that works best is uncoated, unprinted, or printed only with soy-based ink. Waxed cardboard, plastic-lined cardboard, and cardboard with glossy finishes will not break down properly and can introduce unwanted chemicals into your finished compost.

Key Takeaways

  • Plain corrugated cardboard from shipping boxes and paper tubes can be composted and will break down in four to six months with proper moisture and turning.
  • Waxed cardboard, plastic-lined cardboard, and cardboard with glossy or metallic coatings should not be composted because they resist decomposition.
  • Shred or tear cardboard into small pieces before adding it to your pile so it breaks down faster and mixes evenly with other materials.
  • Cardboard is a brown material (high in carbon), so balance it with green materials like food scraps and grass clippings to keep your pile decomposing steadily.

Which cardboard types are safe to compost

Corrugated cardboard—the wavy, layered kind used for shipping boxes—is the most common type you will encounter and composts well. Tear it into pieces roughly 2 to 3 inches across so it breaks down faster. Cardboard from appliance boxes, moving boxes, and online orders all work.

Paper tubes from paper towels, toilet paper, and wrapping paper are fine to compost whole or shredded. They decompose quickly because they are thinner than corrugated cardboard. Cereal boxes and other food packaging made from plain cardboard (no plastic window) can also go in, though you should remove any plastic windows or liners first.

Kraft paper and plain brown paper bags are compostable. Newspaper and plain office paper are also acceptable, though they are not cardboard—they break down even faster than cardboard does.

Cardboard to keep out of your compost

Waxed cardboard has a thin plastic or wax coating on the inside to make it water-resistant. Milk cartons, juice boxes, and some frozen food boxes use this coating. The wax or plastic does not break down in a home compost pile and will remain in your finished compost as fragments.

Plastic-lined cardboard is used for takeout containers, bakery boxes, and some frozen food packaging. The plastic layer prevents decomposition and should be removed before composting the cardboard, if the two can be separated at all. Many of these boxes are not worth the effort—it is simpler to throw them away.

Glossy or metallic cardboard appears on some gift boxes, greeting cards, and specialty packaging. The coating resists breakdown and can introduce dyes or metals into your compost. Cardboard printed with heavy, dark inks or colored inks may also contain chemicals that are better left out of your pile, though light printing with soy-based ink is usually safe.

How to prepare cardboard for composting

Tear or shred cardboard into pieces before adding it to your pile. Smaller pieces expose more surface area to moisture and microorganisms, which speeds decomposition. A piece 2 to 3 inches across is ideal; you can also run cardboard through a paper shredder if you have one.

Wet the cardboard pieces lightly before adding them to your pile. Dry cardboard repels water and will sit in your compost without breaking down. A quick spray from a hose or a dunk in a bucket is enough—you do not want cardboard soggy enough to clump together.

Mix cardboard pieces throughout your pile rather than stacking them in one spot. Cardboard is a brown material (high in carbon), so alternate layers of cardboard with green materials like food scraps, grass clippings, or plant trimmings. A rough ratio of three parts brown to one part green keeps your pile decomposing steadily.

How long cardboard takes to break down

Plain cardboard typically takes four to six months to decompose in an active compost pile—one that you turn regularly and keep moist. If you leave your pile undisturbed, cardboard can take a year or longer. Thinner cardboard like paper tubes breaks down faster than thick corrugated cardboard.

Temperature matters too. A pile that stays warm (between 130 and 150 degrees Fahrenheit) because of active decomposition will break down cardboard faster than a cool pile. If you are composting in winter or in a cold climate, expect the process to slow significantly.

You will know cardboard is fully decomposed when you cannot identify the original shape or texture—it will look like tan or brown crumbles mixed into the rest of your compost. Small pieces of cardboard fiber may still be visible in finished compost, and that is normal.

Using cardboard as a compost base or weed barrier

Many gardeners use cardboard differently than mixing it into a pile: they lay it flat on the ground as a weed barrier before adding compost on top. This works well for starting a new garden bed or suppressing grass before planting. The cardboard blocks sunlight from reaching weeds and gradually decomposes into the soil.

For this use, plain corrugated cardboard is ideal. Overlap pieces by at least 6 inches so weeds cannot push through the seams. Wet the cardboard so it stays in place, then add 4 to 6 inches of compost or mulch on top. The cardboard will break down over one to two years as you water and tend the bed.

Do not use waxed or plastic-lined cardboard for this purpose—the coatings will persist in your soil and prevent water and air from reaching plant roots.

Common mistakes when composting cardboard

The most common error is adding too much cardboard at once. Because cardboard is brown material and breaks down slowly, a pile that is mostly cardboard will decompose very slowly and may start to smell or attract pests. Add cardboard gradually and always balance it with green materials.

Another mistake is composting waxed or plastic-lined cardboard without realizing it has a coating. Check the inside of the cardboard before adding it. If it feels slick or waxy, or if you can see a plastic layer, do not compost it. Glossy finishes are also a sign to leave the cardboard out.

Leaving cardboard in large, unshredded pieces slows decomposition significantly. A whole shipping box can sit in your pile for over a year without breaking down much. Tear or shred cardboard before adding it, and your compost will be ready faster.

Frequently Asked Questions

Can I compost cardboard with colored ink or printing on it?

Light printing with soy-based ink is generally safe to compost. Most modern cardboard boxes use inks that break down without harming your compost. Heavy, dark, or glossy printing—especially on gift boxes or specialty packaging—may contain chemicals better left out. When in doubt, remove the printed section or compost only the plain cardboard underneath.

What about cardboard from pizza boxes?

Pizza boxes are tricky. The bottom is usually plain cardboard and can be composted, but the inside of the lid often has grease or cheese residue. Grease slows decomposition and can attract pests. Tear off the greasy parts and compost only the clean cardboard, or skip pizza boxes altogether if they are heavily soiled.

Can I compost cardboard egg cartons?

Yes. Cardboard egg cartons are made from plain, uncoated cardboard and break down quickly because they are thin. You can compost them whole or tear them into pieces. Styrofoam egg cartons cannot be composted and should go in the trash.

How do I know if cardboard has a plastic coating?

Feel the inside surface with your fingernail or rub it with a damp finger. Waxed or plastic-coated cardboard will feel slick or waxy and may not absorb water. Plain cardboard feels dry and slightly rough. If you can see a visible plastic layer or if the cardboard is waterproof, it has a coating and should not be composted.

Can I compost shredded cardboard from a paper shredder?

Yes, shredded cardboard composts faster than whole pieces because the smaller size exposes more surface area. Mix shredded cardboard with green materials and keep the pile moist. Shredded cardboard can mat together if it gets wet, so stir your pile regularly to keep it loose and aerated.