Can you compost cardboard? Usually…

  • Date: June 8, 2022

During the pandemic online sales went through the roof. With this came the unavoidable issue of packaging waste – and a staple of this is, of course, the cardboard box. But before covid-19 hit our shores, we still used plenty of the stuff – from business cards to cereal boxes. These are commonly recyclable and collected in standard curbside collections. But for the keen gardeners out there, can you compost cardboard? Generally, yes, with one main exception. Let’s have a look…

What is cardboard made of?

Cardboard is the broad term for stronger, paper-based items. The term stretches anywhere from paperboard to thick corrugated cardboard. Generally, cardboard is made from tree pulp – or recycled cardboard, which was originally made from tree pulp. In some cases, the cardboard can be coated with a plastic material to give it a glossy effect and make them more durable.

Is cardboard biodegradable?

A material is biodegradable if it can be broken down by bacteria and/or other micro-organisms. The component parts can return to nature. It perhaps won’t be a surprise that cardboard is, indeed, biodegradable. And not only that, it also breaks down fairly quick too. It depends partly on the conditions, but usually only takes a matter of months! If your cardboard does end up in landfill, although not ideal, it won’t hang around too long – unlike lots of other materials. Glossy cardboard coated in plastic does present some issues. Plastic is not biodegradable, so it will not fully biodegrade.

Can you compost cardboard?

Composting is a great way to dispose of organic waste. As well as providing a nutrient-rich fertilizer it ensures that items can be diverted from landfill. The fact that cardboard is biodegradable does not automatically mean it qualifies for the compost pile. The terms biodegradable and compostable are not interchangeable. To be fit for the compost pile, an item needs to be able to contribute to the final nutrient-rich compost – whilst not contaminating the pile in any way. Thankfully, most cardboard is both biodegradable and compostable.

Composting ingredients fits into two main types: carbon-rich ‘browns’ and nitrogen-rich ‘greens’. Cardboard falls firmly in the ‘brown’ category. As you may know, you need an adequate mixture of the two types for a well-functioning compost pile. Too much carbon can lead to dryness and an ant infestation, whilst too much nitrogen can cause excess heat and a slimy mess! Opting for the simple life, we often recommend a simple 1:1 ratio. Although you will see different ratio suggested elsewhere, this ratio works well and avoids any complicated math. However, even if you are stringently sticking to this ratio, you should always monitor the pile as you go along. No two compost piles the world over are identical – so the ratio is merely a starting point. If you are new to composting, you can find some commonly asked beginners’ questions here.

Cardboard, and paper, are not the most nutrient-rich composting ingredient out there. But they do play a very important role when added. Not only providing carbon, but also helping provide some structure. The gaps created allow increased airflow and aid the composting process.

Some considerations when composting cardboard…

Like other compostable items, you can speed up the process by cutting the cardboard into smaller pieces. As well as providing a larger surface area for the microbes to act on, it also means you can mix it throughout the pile. The benefits of cardboard, such as soaking up excess moisture, can be spread out. If you don’t have an adequate shredder for the job, a utility knife or a heavy-duty pair of scissors will do the trick. Although it helps, it is not strictly necessary – the cardboard will breakdown regardless.

All cardboard is not created equally when it comes to disposal. We would recommend leaving glossy cardboard out of the compost pile. The plastic element, although small, will not breakdown. Plastic simply break ups into smaller pieces eventually. This could contaminate the pile – and with recycling an option, it just isn’t worth the risk. As ever though, it’s your call!

Finally, you should consider the amount of cardboard you are adding. As with any item, too much may be detrimental to the health of the pile. It depends largely on the size of your compost heap and other ingredients being added but we would recommend erring on the side of caution initially. Don’t add your whole hoard of cardboard boxes at once!

The bottom line

Apart from reuse, there are two main planet-friendly ways to dispose of cardboard. Recycling is, arguably, more eco-friendly – it reduces the amount of new cardboard that needs to be produced. However, if your compost needs an injection of carbon and you have a cardboard box to get rid of, then throw it in there! Although it would biodegrade in landfill, it is much better to avoid this when possible.