Can you compost cardboard?

Why

Cardboard is wood fibre. At roughly 350:1 carbon to nitrogen it is strongly on the brown side, which makes it the natural counterweight to a kitchen caddy full of wet greens.

Corrugated board has a second advantage nothing else matches: the flutes create air channels that resist compaction, which is the usual cause of a sour pile.

How to add it

Tear or shred it, smaller pieces break down far faster. Wet it before adding, or it will sit dry and unchanged for months.

Remove plastic tape, staples and plastic-lined windows. Brown packing paper and egg boxes count too.

Common mistakes

Adding it dry and in large flat sheets. Flat wet cardboard forms an impermeable mat that water cannot pass through.

Assuming all card is fine. Glossy, heavily printed and laminated board is best kept out, see below.

Which cardboard to avoid

Glossy or waxed board, anything with a plastic laminate, and thermal receipt paper. Standard soy-based printing inks on plain board are not a meaningful concern; the widely repeated warning about ink toxicity mostly predates modern inks.