Is Cardboard Biodegradable & Can It Be Composted?

is cardboard biodegradable

From packaging, toilet roll tubes and drinks cartons, cardboard is a material we’re all very familiar with in and around the home.

You’re right to think that cardboard is highly recyclable as it comes from trees, but does this make cardboard biodegradable too? Can it even be composted?

For many, this may seem like a straightforward question. However, because cardboard has so many different uses and purposes it’s not all exactly the same, which makes the question a little more difficult.  

By the end of this short post you’ll understand how biodegradable cardboard is and if this makes it an eco friendly material. Let’s get straight into it.

Is cardboard biodegradable or non-biodegradable?

On the whole, cardboard is a highly biodegradable material.

Plain old cardboard is made from wood pulp which is absolutely biodegradable.

However, not all cardboard is the same. Some cardboard, for example the type used for drinks cartons, is covered in a layer plastic or waxy material to make it waterproof.

This is true for single-use coffee cups too. They feel like cardboard on the outside, but on the inside is a shiny layer of plastic. It’s very difficult to remove this layer, which is why they are so problematic to recycle and why you’re always much better using a reusable coffee cup with some great organic coffee!

In other situations, cardboard can be contaminated with other substances, such as oil and grease, which make it more difficult to biodegrade.

For cardboard to biodegrade fully, it will have to be clear of all non-natural contaminants. It needs to be free of the additional materials that sometimes come with cardboard, including tape, paint, glue, glitter, polystyrene and any plastic coatings.

Can you compost cardboard?

With the majority of cardboard classed as biodegradable, does this mean it is compostable too?

If you’re a little unsure of the difference between biodegradable and compostable, let me briefly explain.

Given enough time, almost everything is biodegradable. All biodegradable means is that microorganisms will breakdown the material. There are no time constraints to this, which is why biodegradable often gets misused when it comes to products and the marketing behind them. For example, you might see plastic dog poo bags labelled as ‘biodegradable’, when in fact it’s not what you think.

A much more well-defined term is compostable. Something can only be classed as compostable if it breaks down into non-toxic constituents that cause no harm to the environment within a certain time period. For a product to be labelled as compostable, 90% of the material must have broken down within 12 weeks in an industrial composter.

cardboard toilet roll tube is biodegradable
Many household items are made from cardboard

So, is cardboard compostable then?

In general, yes cardboard is compostable.

Coming from tree trunks, cardboard is a wood-based carbon-rich material. Have a read here to see how recyclable wood is.

If it’s not coated with any unnatural materials, cardboard will breakdown naturally into carbon dioxide, water and organic waste. Just make sure there isn’t any tape, white polystyrene or plastic still stuck to the cardboard.

How long does it take cardboard to decompose?

As per the compostable definition, cardboard will decompose in an industrial composter within 12 weeks.

However, you may be thinking more about your garden compost pile. Here, you may not have the precise conditions that an industrial composter can work to. For this reason, it may take a little longer for cardboard to decompose in your garden compost heap.

On the quick side, cardboard will decompose within 3 months. More realistically, you may be looking at 6 months and up to a year.

compost piles different stages
Uncontaminated cardboard can be shredded and added to your garden compost pile

It all depends on the levels of heat, moisture, oxygen and microbe content of your compost pile. If the levels are optimal, the organic material will break down faster.

You can help cardboard along beforehand by shredding it up and soaking it in water before you add it to your soil or pile. Shredding and ripping the cardboard up helps to increase the surface area so more microorganisms can get at it straight away. Microbes also love water, which is why soaking it will help them to thrive and eat there way through the cardboard.

Any cardboard with shiny, waxy coatings will take much longer to decompose. These types of cardboard can take a number of years to fully decay.

Doesn’t some cardboard contain glue?

Some cardboard types, such as corrugated cardboard, do contain glue. Does this mean they are not biodegradable or compostable?

It all depends on the type of glue used.

Most commonly, the glue used in corrugated cardboard is starch based. This means it has been derived from starchy vegetables, such as corn or potato.

If the glue is starch-based then it is fully biodegradable and compostable, as the glue will breakdown into non-toxic substances at the same rate as the other organic materials.

Some other wood products, such as plywood, also contain glue. However, the glue used in plywood is mostly synthetic, fossil-fuel based. Have a read here to see if plywood is sustainable.

Did you know – compostable food caddy bags are also made from starchy vegetables (often potatoes) which is why they can be composted.

Does this mean cardboard is eco friendly?

Whether a material will naturally biodegrade in the environment is just one aspect of assessing its eco-friendliness.

If a material can biodegrade into non-toxin substances and re-enter the ecosystem without having a negative impact, then great.

If a material can decompose into its constituent organic parts and go on to have a positive impact on the natural environment, then even better.

However, you also have to consider where the raw material comes from. Are these sustainably produced? What are the carbon emissions like? How long will the product last for?

corrugated cardboard is biodegradable if made with starch based glue
Corrugated cardboard is still biodegradable if it’s made with starch-based glue

When it comes to cardboard the answers to these questions may vary depending where it’s made and by which company.

As you know, the raw material to make cardboard is trees. These are usually fast-growing species, such as pine.

On balance, cardboard is an eco friendly material. Particularly when compared to the synthetic material that may replace it otherwise.

Cardboard is often reusable, fully recyclable, biodegradable, compostable, doesn’t contain any toxins and doesn’t have any direct negative impacts on the environment. 

So, there you have it. If you can, reuse cardboard first but when it’s finished being useful for it’s main purpose, cardboard is fully biodegradable.  


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