Cardboard does not belong on your soil. Period. (2024)
In the quarter century that I’ve been researching, publishing, and educating on the topic of landscape mulches, one thing has become clear: cardboard should never be used as a mulch. This viewpoint has been of great interest to gardeners; in fact, my earlier post has been the most frequently viewed post since it was published in 2015. I occasionally appended new information to the original post as needed, but the topic deserves an update.
Rather than rehashing what’s been written earlier (which can be found here, here, here, here, and here in addition to the link above), I’m providing information in a Q&A format that might be helpful:
Q: Is there research on using cardboard mulch in home landscapes?
A: Not much. To date, the only peer-reviewed research relevant to landscape soil conditions is our own work published in 2019. The abstract explains the importance of the results to landscape soil health as stated in the abstract (below):
“The orders of magnitude differences in diffusioncoefficients among the mulch materials, however, could negatively impact adiverse soil environment such as those found in biologically rich landscapeswith higher oxygen demands. Among the mulches tested, wood chips are apreferred method of mulching in terms of providing best gas permeability,particularly in landscape conditions.”
Q: Cardboard has been used as a mulch in agricultural production. Why doesn’t that research support using it in landscapes?
A: The goal in agricultural production is to maximize yield of an annual crop. In contrast, the goal in caring for a permanent landscape is to maintain a healthy soil ecosystem that will support plant life long term. The table below explains these differences in more detail.
Q: Okay, I understand that science doesn’t support using cardboard as a landscape mulch, but what about my vegetable garden? Isn’t the research on agricultural crops relevant there?
A: The research on agricultural production mulches is more relevant if maximizing yield is your most important goal. But your goals may include maintaining a healthy soil ecosystem, reducing the use of pesticides and fertilizers, and other criteria. Are you concerned about the established negative impacts that cardboard and other sheet mulches have on soil life? If so, then sheet mulches are not a good choice compared to chunky, three-dimensional mulches.
Q: I like reusing cardboard packaging as part of organic weed control. Isn’t that a good enough reason to use cardboard?
A: In addition to interfering with water and gas movement into the soil environment, corrugated cardboard has chemical contaminants that you really don’t want in your soil or even your compost pile. Corrugated cardboard contains environmental contaminants including dioxin and PFAs or “forever chemicals.” No gardener should want to introduce more of these widespread contaminants into their landscape or garden soils.
As I’ve been recommending for nearly a quarter century now, the very best mulch to use for treed landscapes is arborist wood chips. There is robust, peer-reviewed science establishing the benefits of arborist chip mulches in controlling weeds, enhancing growth and establishment of landscape plants, and maintaining a functional soil ecosystem. In contrast, sheet mulches such as plastic, weed fabric, and cardboard have demonstrated negative impacts on the long-term health of landscape soils. Any resource that says otherwise is not paying attention to the research-based facts.
Q: I like reusing cardboard packaging as part of organic weed control. Isn't that a good enough reason to use cardboard? A: In addition to interfering with water and gas movement into the soil environment, corrugated cardboard has chemical contaminants that you really don't want in your soil or even your compost pile.
Shred the cardboard and add it as an important carbon source to your compost bin. Another idea for reusing cardboard for the garden is to place pieces of it around plants in areas that are prone to weeds. It will reduce weeds drastically and eventually compost into the soil.
A garden or landscape mulched with cardboard (or heaven forbid several layers of cardboard as part of the science-free lasagna mulch method) is now covered with a tough, relatively gas- and water-impermeable material that will take some time to break down. It's hardly a mulch that's going to nurture soil life.
Cardboard takes approximately 2 months to decompose. However, instead of sending your boxes to the landfill consider adding them to your recycling or your compost pile. Cardboard breaks down fairly quickly when exposed to the elements, but stacks of cardboard can take years to decompose.
Using cardboard or newspaper as a natural weed barrier can allow you to kill a very large area of weeds and grass without using any chemicals or herbicides. Cardboard is applied to the area.Then a layer of mulch goes on top of that. In creating a highly fertile site, a gardener may put several layers of materials.
The answer is yes. You can line the bottom of your raised garden bed with cardboard and newspaper to block out weeds or act as a barrier against rhizomatous, weedy or invasive plants. While some may opt for landscape fabric, cardboard is a more cost-effective option.
Cardboard weed barriers are a better option for vegetable gardens where crop rotation necessitates that the plants in the plot be moved around regularly to combat plant pathogens in the soil. Many larger vegetable plants also have deep roots that you would have to cut a landscaping fabric to allow for.
Decomposing cardboard adds organic matter to the soil, improving your garden's drainage and boosting nutrient levels. Earthworms flock to the dark, moist, safe habitat cardboard provides, leaving behind a nutrient-rich layer of worm castings–free fertilizer!
When should I put cardboard in my garden? The ideal time for preparing a garden bed is at least 6-8 weeks before planting. However, the longer the cardboard, compost, and mulch have the opportunity to break down, the better results you will have.
Termites are attracted to paper and cardboard because of their high cellulose content. Unused boxes, stacks of paper, or even wallpaper can draw termites. It's best to store paper and cardboard items in sealed plastic containers and minimize clutter to avoid attracting these pests.
You are trying to prevent sunlight from energizing those weeds!” “In general, smothering weeds with cardboard is a good idea at any point. The cardboard will eventually decompose, yes, but you want it to smother the weeds first, before it becomes compost!
1) Newspaper and cardboard sheet mulches can become pest havens. Termites were found to prefer cardboard over wood chips as a food source, and rodents such as voles often nest underneath mulch sheets.
Cardboard is often made with pulp from pine trees, which can create a toxic gas called sulfur dioxide. When cardboard is dumped in a landfill and left to degrade, it releases this gas into the air, which can cause pollution when it reaches the air…or the soil below the landfill.
If you know one thing about red worms, it's that they're crazy about brown cardboard. After all, why not? It's the perfect bedding, the perfect jungle-gym, and the most readily available foodstock.
Why Is Cardboard Good For Compost? If you want to add a good carbon source to balance your nitrogen-rich materials in your compost, cardboard waste makes that happen. Cardboard is also an organic way to start building layers in your compost.
Introduction: My name is Jonah Leffler, I am a determined, faithful, outstanding, inexpensive, cheerful, determined, smiling person who loves writing and wants to share my knowledge and understanding with you.
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