Is it Safe to Use Cardboard in Your Garden?

Join horticulturalist Lorin Nielsen to find out if it's safe to use cardboard in the garden. In this guide, we will discuss the pros and cons to consider.

Written by Lorin Nielsen Last updated: May 6, 2025 | 3 min read

A shot of a person in the process of rolling a carton in a yare area, showcasing cardboard safe garden

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If you’ve spent any time researching sustainable gardening practices, you’ve likely encountered the recommendation to use cardboard as a mulch or weed barrier. This abundant material seems like a perfect solution for eco-conscious gardeners – it’s free, readily available, and keeps waste out of landfills. But is cardboard actually safe to use in your garden? Let’s dig into the facts.

What Is Cardboard Made Of?

A shot of a carton box placed in a grassy area outdoors — Basic brown cardboard is biodegradable.

Before determining whether cardboard is safe for garden use, we need to understand its composition. Most cardboard is made from:

Wood pulp (the primary component)
Starch-based adhesives (to bond layers together)
Printing inks (for labels and designs)
Various coatings (especially on glossy cardboard)

Standard brown cardboard boxes contain primarily cellulose fibers from wood pulp, which are natural and biodegradable. According to the OSU extension service, basic brown cardboard is essentially compressed paper and breaks down into organic matter in the soil over time.

Benefits of Using Cardboard in the Garden

Excellent Weed Suppression

A shot of several cartons laid out on a yard area, weighed down with several rocks and stone, all placed in a well lit yard area outdoors — Cardboard forms an effective barrier that prevents the germination of weeds.

When laid properly with overlapping seams, cardboard creates an effective barrier that blocks light from reaching weed seeds, preventing germination. Cardboard can be particularly effective at suppressing aggressive perennial weeds when used as a sheet mulch.

Soil Building and Carbon Sequestration

A shot of several cartons placed on a yard area, being weighed down with rich soil in a well lit area outdoors — Cardboard helps improve soil health and structure as it breaks down.

As cardboard breaks down, it adds carbon to your soil. This helps improve soil structure and feeds beneficial soil microorganisms. The decomposition process also attracts earthworms, which create tunnels that enhance soil aeration and drainage.

Moisture Retention

A shot of a person in the process of watering laid out carton boards with a watering can, all situated in a well lit area outdoors — Carton boards help retain soil moisture by reducing evaporation.

Cardboard helps soil retain moisture by reducing evaporation, which means less frequent watering for your plants. This is especially beneficial during hot summer months or in drought-prone regions.

Cost-Effective Solution

A shot of several empty cartons piled on top of each other in a yard area outdoors — A cardboard layer is a budget-friendly, accessible option.

Most gardeners have access to free cardboard from packaging, making it an extremely budget-friendly option compared to commercial weed barriers or mulches.

Habitat Creation for Beneficial Organisms

A shot of several carton boards laid out in a yard area outdoors — Carton boards create a dark, moist environment beneath them, where earthworms and beneficial insects thrive.

The dark, moist environment created beneath cardboard is ideal for earthworms and beneficial insects. These organisms help break down the cardboard while improving soil health.

Potential Drawbacks

Chemical Treatments and Inks

A shot of several waste cartons tied up together, and is placed in a well lit area outdoors — Remove any glossy or heavily colored portions before using in the garden.

Some cardboard contains chemicals like dyes, inks, tapes, and glues that you might not want in your garden soil. While most modern inks are soy-based and considered safe, it’s still advisable to remove glossy or heavily colored portions.

Possible pH Alterations

A shot of several pile carton boards in a yard area outdoors — As the material breaks down, it can affect the soil pH.

As cardboard breaks down, it may temporarily affect soil pH. Some gardeners report slight pH changes, though this is generally minimal and not a significant concern for most plants.

Nitrogen Depletion

An overhead shot of a decomposing carton box in a well lit area outdoors — Temporary nitrogen depletions in soil can happen as the material decomposes.

During decomposition, cardboard (which is high in carbon) requires nitrogen to break down. This can potentially lead to temporary nitrogen depletion in your soil, which might affect plant growth if not addressed. Adding a nitrogen-rich material like compost can help counter this effect.

Pests

An overhead shot of a snail on top of a sheet of carton in a yard areaa outdoors — Cardboard can become a haven for several pests.

The space between cardboard and soil can become a haven for certain pests like slugs, earwigs, and sowbugs. Regular monitoring can help identify and address pest problems early.

Best Practices

A shot of an empty carton box placed in a yard area outdoors — Remove all tape, staples, and stickers before use.

To maximize benefits and minimize potential issues:

Use plain brown cardboard whenever possible, avoiding glossy or heavily printed materials.
Remove all tape, staples, and stickers before laying cardboard in your garden.
Wet the cardboard thoroughly before and after placement to kickstart decomposition.
Cover with organic mulch like wood chips, straw, or compost for better aesthetics and faster decomposition.
Add nitrogen-rich materials such as compost or well-rotted manure to prevent nitrogen depletion during decomposition.

The Bottom Line

An overhead shot of an empty carton box placed in a grassy area outdoors — Generally, cardboard is safe, sustainable, and effective.

For most gardeners, cardboard is a safe, sustainable, and effective material for the garden when used properly. Cardboard sheet mulching can be an environmentally friendly approach to establishing new garden beds and controlling weeds.

While there are some considerations to keep in mind, the benefits typically outweigh the potential drawbacks, especially when using plain brown cardboard and following best practices. As with many gardening techniques, observation and adaptation based on your specific soil and plant needs will help you achieve the best results.

So go ahead – save those boxes for your next gardening project! Just be sure to remove the tape, and consider adding a layer of compost or attractive mulch on top for both functional and aesthetic benefits.