how long does it take for cardboard to decompose

We live in a world of convenience where we can have practically anything we want delivered straight to our front doors.

But, once we’ve unboxed our newest purchase, the question of what to do with the cardboard packaging it arrived in comes to mind. 

Cardboard is one of the most recyclable materials available, and whilst that’s undeniably beneficial for the health of the planet, not everybody has the access to a recycling centre and, as such, cardboard is often discarded of in our general household waste. 

There is another way of disposing of unwanted cardboard packaging though. Why not try adding it to your compost bin instead?

This will transform it into a super useful soil additive that you can use all around your garden in a variety of ways and will help to reduce your carbon footprint even further in the process. 

Once it’s on your compost heap, however, just how long does it take for cardboard to decompose? And how do you prepare it for the composting process? 

Fear not! We’ve got all the answers to any cardboard composting questions you might have below, along with all the information you need in order to use this fantastic material around your garden and reap the benefits along the way. 


How long does cardboard take to decompose outside of a compost bin?

To answer this, we need to look at the sort of cardboard that has been disposed of.

There are also environmental factors to consider, such as moisture and heat, as well as the state that the cardboard was in when it was discarded.

Heavily processed cardboard, such as milk cartons or juice boxes will have been treated with a special wax in order to make them leak-proof. Whilst that’s super handy when they are in use, it also means that it takes them longer to decompose naturally.

On average, a piece of heavily processed cardboard will take about 5 years to decompose. 

Untreated cardboard will take less time to break down, usually within a year or two. This can be quicker if it has been subjected to extreme weather conditions such as heavy rain, which will cause it to erode away. 

How long does it take for a compost bin to decompose cardboard?

The decomposition rate of cardboard within a compost bin is much faster than cardboard that has been disposed of in your general waste.

This is because the microorganisms that live in your compost bin will speed up the breakdown process, and turn it into compost along with any other organic materials in as little as 4-6 months. 

Again, this does depend on the type of cardboard that you’re composting, with wax-coated cardboard taking longer than untreated cardboard to decompose.

However, the internal heat and moisture in the core of your compost bin will speed up the process and still help it decompose faster than wax-coated cardboard disposed of any other way. 

How do you compost cardboard?

Composting cardboard is super easy and, although there is a little bit of work that needs to be put into it, it’s nothing that is particularly labour intensive. 

The most important thing you need to do is make sure that the cardboard you’re composting has been broken down into smaller pieces.

This will help the microorganisms in your compost bin break them down with greater ease, which in turn will give you compost at a faster rate. 

You can also soak your cardboard in water before adding it to your compost bin to help speed up the process.

This is particularly useful if your compost bin has a waterproof lid, however, if you have an open pile of compost the rain will eventually do this for you. 

Any cardboard that you’ve added to your compost pile will also need to be kept moist to speed up the decomposition process.

This can be achieved by turning your compost every 2-3 weeks and sprinkling a little water over the top if necessary. You don’t want it to be soaking wet, just moist enough to feel damp to the touch.

What types of cardboard can be composted? 

All types of cardboard are compostable, some just take a slightly longer time to decompose than others.

Below, we’ve listed the three main types of cardboard you’re likely to be adding to your compost along with the average time it will take to break down into usable compost.

  • Corrugated Cardboard: This is the most common type of cardboard used for packaging. Once broken into smaller pieces and added to your compost it will usually take no longer than 6 months to fully decompose.
  • Flat Cardboard: Cereal boxes, shoe boxes, and other flat-sided boxes are constructed using flat cardboard. It’s a little tougher than corrugated cardboard, but once broken down into smaller pieces and place into your compost bin it will fully decompose in around 6-8 months.
  • Wax Coated Cardboard: This is the toughest of all three and the wax coating makes the cardboard much more resistant to water damage and erosion. Again, you’ll need to break this down into smaller pieces, and it will fully decompose in a compost bin in about 12 months. 

What else can I use cardboard for in my garden?

Cardboard has loads of other uses around the garden in its full form too, so even if you don’t have a compost bin you can still spare it from your household waste and reap the benefits of using it in your outdoor space. 

One great alternative use of cardboard in the garden is to shred it and use it as a mulch around potted plants and raised beds in late fall to help prevent any frost damage occurring on the roots of perennials plants.

The winter rain and snow will eventually aid in its decomposition too, and come spring it will have worked its way into your soil. 

You can also use certain cardboard products, such as toilet roll or kitchen paper tubes, as alternative seed starters. Stand them upright, fill them with soil, and sow your seeds into them.

This is a fantastic way to reduce your plastic waste, and you can even plant them directly into your garden soil in spring with the seedling inside, as they will decompose away over the course of the year. 

Final Word

The way in which you choose to dispose of your cardboard will ultimately determine how long it will take for it to decompose. If thrown out with your regular household waste, it could take up to 5 years for it to decompose fully. 

However, given a bit of effort and the right equipment, you can speed up the process to less than a year and use it in and around your garden.

This helps reduce your carbon footprint, and will even help to protect your plants for years to come. 

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