Compost Cardboard (how long does it take to decompose)

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If you’ve ever found yourself surrounded by piles of cardboard, you might wonder how to dispose of it responsibly. Well, good news! Aside from recycling, you can also compost cardboard, which is a great, responsible option. As you consider adding cardboard to your compost heap, knowing what to expect is essential. I will provide the insights you need to break down your cardboard waste effectively and contribute to a healthier environment.

Generally, plain cardboard takes about 2 weeks to 2 months to decompose, while wax-coated takes up to 5 years or longer. However, soaking cardboard in warm water can accelerate the decomposition process. Avoid creating huge stacks of cardboard, as it will take years to break down completely.  

large pile of different sized brown cardboard boxes with dark wood background

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Today, I’m eager to share some helpful and practical tips on preparing your cardboard for composting and ensuring it breaks down faster and more efficiently. Understanding these easy steps will allow you to set up your pile effectively while transforming your cardboard waste into nutrient-rich soil.

Humble Highlights

  • Save time and discover how long it takes for cardboard to REALLY decompose so you can prep your boxes BEFORE mixing them in your compost for faster results and a happier garden! 
  • Discover the two primary types of cardboard you can add to your compost and the proper steps to help enrich your soil while becoming eco-friendly.
  • Discover how to ally with the surrounding environment with these 3 environmental benefits of composting cardboard so you can build your garden and reduce household waste easily and effectively! 

Factors Affecting The Decomposition Process Of Cardboard: How Long Does It Take

Whether your cardboard is whole or torn into smaller pieces, whether flat or waxed, the status of your cardboard significantly affects the speed of decomposition. Shredding cardboard into smaller pieces helps to increase the porosity, allowing for more air to circulate and proper moisture distribution, facilitating microbial activity and speeding up the decomposition process. 

can you compost cardboard

On the other hand, stacks of intact cardboard take much longer to break down due to their larger size and reduced surface area, which means there is less area for microorganisms, moisture, and other factors involved in the decomposition process to act upon. 1

Humble Tip:
Cardboard decomposition can take about 5 years or more if you don’t consider these key factors. Given that there are various types of cardboard products today, it’s important to be selective with cardboard types, avoiding those with harmful additives or colors like Red 40 or Yellow 5, which can have health concerns and can be transferred into your garden unknowingly.

Different Types Of Cardboard

Although cardboard mainly comprises organic materials, it may include additives such as adhesives, inks, and coatings for printing and protective purposes. Below are different types of cardboard you can find in your home or yard.

how to shred cardboard for compost

Corrugated Cardboard

Corrugated cardboard is primarily made from organic materials, such as paper pulp derived from wood fibers. These organic components are biodegradable, meaning they can naturally break down into simpler substances over time.

In a compost pile, microorganisms, such as bacteria and fungi, play a crucial role in breaking down organic matter. Cardboard provides a structure that these microorganisms can colonize, aiding in decomposition. 2

Here’s how the breakdown process typically works for this type of organic matter.

  1. Collect clean cardboard waste free of contaminants like plastic and inks, and remove any cardboard packaging tape or labels.
  2. Tear it into smaller pieces for quicker decomposition and a more uniform organic matter mixture.
  3. Apply your sheets of cardboard first, then add a layer of soil.
  4. Add the pieces to your pile of organic matter, ensuring a balanced mix of brown (cardboard) and green (nitrogen-rich) materials.
  5. Mix in some green materials like kitchen scraps and untreated and chemical-free grass clippings to balance out the cardboard’s carbon-rich nature. This helpful step keeps the mixture of your organic matters in the right balance and your pile decomposing correctly.
can you compost cardboard with ink

Wax-Coated Cardboard

To determine cardboard’s  decomposition time, consider the presence of wax and surrounding environmental conditions. Remember,  it takes a long time to break down due to the water resistance provided by the wax coating. 3

Here are three key points to understand about decomposition time: 

  • Years: Wax-coated cardboard can take years to break down fully as an organic matter. Wax slows down the breakdown process, and I would not recommend adding it to your compost. 
  • Soil: Although wax-coated cardboard takes a significant amount of time to decompose, once the process is complete, it will provide nutrients to the soil, such as carbon, nitrogen, and organic matter. Additionally, minerals will be added, including calcium, magnesium, and potassium, improving its health and fertility.
  • Environmental factors: Its decomposition time can be influenced by surrounding environmental conditions, such as moisture levels and other organic materials, including organic manures from cows, horses, or poultry, kitchen scraps, used or unused newspapers, or even toilet paper.

Used Cardboard Boxes Without Wax Lining

Cardboard without a wax lining typically decomposes within 2 weeks to 2 months, depending upon the efficiency of your pile. This length of time varies because cardboard is biodegradable and undergoes a natural decomposition process when exposed to the proper environmental conditions.

Many items today receive cardboard boxes along with our online and offline orders. Unfortunately, many also toss these useful carbon sources in the trash. If you cultivate a home garden, you can decrease household waste and reuse these boxes by incorporating them into your compost. Check out the video below, which shares some valuable tips you can use today!

Quick Tip: Shred Cardboard To Decompose Faster

You can enhance microbial activity by breaking it down into smaller pieces to expedite the decomposition process. Shredding your cardboard into smaller strips or pieces increases the surface area for microbes to work on, allowing it to decompose more quickly. 

Additionally, soaking it in warm water for 15-20 minutes can make it easier to tear and help remove any labels or stickers, further accelerating the decomposition process. 4

Humble Tip:
Properly managing your cardboard pieces is essential for efficient decomposition. For example, large portions of cardboard may take longer to break down. Also, when exposed directly to the environment, cardboard can become susceptible to harmful organisms such as pests and fungi. 

Composition Of Cardboard: Good For The Soil When Paired With High-Carbon Materials

Cardboard is composed primarily of cellulose fibers derived from wood pulp, making it a biodegradable material. Composting cardboard boxes can benefit the soil when paired with high-carbon materials such as newspapers, paper towels, and dry leaves. 

is it better to recycle or compost cardboard

As cardboard breaks down, it transforms into nutrient-rich organic matter, enhancing soil structure, water retention, and nutrient availability. It also boosts microbial activity and supports beneficial soil organisms. 5

Additionally, cardboard serves as weed-suppressing mulch when layered on soil and enriches it over time. It’s also a suitable bedding material for worm composting with red worms, yielding nutrient-rich castings for garden soil.

Humble Tip:
Cardboard recycling is one of many sustainable options available. Whether you have flat or coated cardboard, its composition makes it sustainable for composting by reducing waste, providing valuable nutrients to the soil, and helping control weed growth.

Environmental Benefits Of Composting Cardboard

The life cycle of cardboard starts when it is made from wood pulp and other natural materials. When it is no longer helpful, instead of tossing it in the trash, adding it to your compost pile is just as easy and eco-friendly. 

can you put cardboard in compost pile

Composting your cardboard biodegradable boxes not only diverts them from landfills but also provides valuable nutrients to the soil. The decomposition process of uncoated cardboard is influenced by factors such as moisture, heat, and other biological materials within your heap. 6

Whether made from recycled paper or virgin fibers, cardboard waste is an excellent addition to your compost bin or pile, offering several environmental benefits.

Here’s why:

  • Reduces landfill waste: One way to repurpose cardboard is through composting. If not, it will be thoughtlessly thrown into landfills, producing methane, a potent greenhouse gas that significantly contributes to environmental climate change.
  • Helps create nutrient-rich soil: No matter how long cardboard takes to decompose, once it does, it releases essential nutrients into the ground, enriching it and promoting healthy plant growth.
  • Balances compost materials: Cardboard provides a valuable carbon source that balances nitrogen-rich materials in compost piles, creating a balanced and nutrient-rich soil amendment.
how long for cardboard to compost

Conclusion

Composting cardboard is an easy, effective method for reducing landfill waste and enhancing garden soil quality. Its breakdown time can vary because different cardboard types have varying decomposition rates. Plain cardboard can break down in as little as two weeks or up to two months, but waxed ones could take longer to decompose and break down completely.

To expedite the decomposition process and make the most of it as a compostable resource, pre-soak cardboard in warm water. Consequently, cardboard-made waste exemplifies environmental sustainability and enriches the soil with valuable nutrients, promoting a robust and healthy garden ecosystem.

Embracing cardboard as a compostable material underscores the importance of sustainable waste management practices. It represents another step toward gardening in a greener, more fulfilling way, caring for our environment.

Do you currently recycle or compost excess cardboard? We’d love to hear the best eco-friendly way you go about being a responsible grower. Please take a moment now and drop us a line in the comments and share your unique story!

SOURCES

  1. MDPI – Waste Management Through Composting: Challenges And Potentials
  2. Wikipedia – Corrugated Fiberboard
  3. Wikipedia – Cardboard
  4. Oregon State University, OSU Extension Service – Sheet Mulching – AKA Lasagna Composting – Builds Soil, Saves Time
  5. University Of New Hampshire – Composting For The Home Gardener [Fact Sheet]
  6. Allotment Garden – Using Paper & Cardboard In Compost

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