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.
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.
It acts as a physical barrier to block out pernicious weeds. Usually, 2 – 3 layers of cardboard will suffice, though you may want layers in more weed-prone areas. The damp environment created by the cardboard is conducive to earthworms and other beneficial soil microorganisms.
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 can effectively prevent weeds from growing. It blocks the sun from reaching the leaves of the plants underneath, hindering photosynthesis and the plants' ability to grow. It's also difficult for seeds to germinate on the cardboard. However, if organic mulch is added, they may still germinate.
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.
Cardboard or newspaper: Cardboard is a great option if you are on a budget. You can line the bottom of your raised garden bed with cardboard and newspaper to deter pests and weeds. In order to minimize the amount of chemical substances, choose cardboard that has no tape and minimal markings.
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.
By simply installing a layer of cardboard on the soil and covering with mulch, you can prevent weeds from poking through for up to 6 months. An unlike rolling out and cutting around plants with fabric, you can place cardboard pieces easily and quickly wherever you need the protection.
Two layers of cardboard works well. Wet down the cardboard as you go to keep it in place and to shape it around obstacles. Work around existing plants by ripping and folding the cardboard. It's easier to rip once wet.
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!
In a home garden, cardboard used as mulch – shredded and soaked with water – the cardboard can decompose rather quickly and be completely broken down by microorganisms within 3 months.
You Can Use a Layer of Cardboard at the Bottom of Raised Beds to Prevent Weeds. If your budget doesn't allow for weed barrier cloth, you can add several layers of cardboard to the bottom of your raised bed before filling it with soil. The cardboard will decompose in about 4 to 6 months.
When starting your bed, cardboard is a key component. Masabni said using cardboard in your no-dig garden creates a physical barrier against weeds for protection. You can also use cardboard on the top of your garden instead of mulch to further prevent weeds.
On the positive side, cardboard is biodegradable and recyclable, with a high recycling rate of 92.9%. However, the production of cardboard is not without its environmental costs. It involves consuming large amounts of water and energy, and using virgin wood pulp contributes to deforestation and habitat destruction.
Introduction: My name is Gregorio Kreiger, I am a tender, brainy, enthusiastic, combative, agreeable, gentle, gentle person who loves writing and wants to share my knowledge and understanding with you.
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