The Paper-Compost Connection

Can you compost paper and cardboard?

Some kinds of paper products are not welcome in recycling programs. Waxed cardboard and pizza boxes are two items that are often on the ‘not wanted’ list. Can such items be composted? The short answer is: Yes. The compost process breaks down materials that come from living things. Paper and cardboard are made from plant fibres. Usually these are derived from wood but some more exotic papers are made from flax, rice or hemp fibres. So, given their origin, paper products should be compostable. Experience bears this out. I line my kitchen scrap collector with newsprint and put in into the compost bin along with the food waste. When the compost process is complete, the paper liner is gone, as are the paper coffee filters and a few paper towels that were also sent off to the compost bin. Pizza boxes and paper plates, napkins and towels are often included in curbside organic collections, and compost successfully along with the other materials.

Can you compost paper and cardboard on their own?

Basically, the answer is no. Cardboard and paper products contain very little nitrogen. The compost process is really about meeting the needs of the bacteria and fungi doing the ‘job’. These microbes like a diet that provides appropriate amounts of two major food groups: carbon and nitrogen. The mix one aims for provides about 30 times as much carbon as nitrogen, or in more technical terms, a C:N ratio of 30:1. Living things are not pure carbon or nitrogen. As composters, we try to mix and match available ingredients to make a good mix. At first glance 30:1 may seem like a high carbon to nitrogen ratio. That understanding quickly changes when you look at a chart of values like the one included here. As you can see, wood and paper products have very high C:N ratios such as 500:1. Formulas exist to help you calculate the appropriate volumes to mix. A good on-line resource is found at Klickitat County's website. This particular compost calculator takes into account the fact that some sources of carbon, such as wood chips, are not very accessible in the short run.

What would be a good mix?

This mix, with a desirable C:N Ratio of 31:1, was devised with the calculator mentioned above:

• 4 parts Cardboard
• 50 parts Grass, loose
• 50 parts Leaves, fresh
• 50 parts Leaves loose-dry

Do you need to shred cardboard before composting?

It is a good idea but not absolutely necessary. Unshredded material will take longer to compost and may make material more difficult to handle. Cardboard can be shredded with a hammermill.

Are there concerns about toxins in the finished compost?

There is no definitive answer to this question, but generally speaking because of the switch to soy- and canola-based inks, many of the old concerns are no longer valid. Waxed cardboard also seems to be a safe ingredient. (See research paper)

(Source: Feb. 2008 WasteWatch)

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