How to Use Cardboard in the Garden to Prevent Weeds and Enrich the Soil

Do you have excess cardboard lying around your home? Rather than throwing it away, consider using it in your garden. Cardboard is made from wood fibers and processed into a thin, strong sheet. It is biodegradable and breaks down over time, allowing it to have several applications in the garden. Ahead, our experts share all the ways you can use cardboard in the garden, such as preventing weeds, enriching your soil, and more.

Establish a New Garden Bed

Starting a new garden bed can be a lot of work, but cardboard can make the process easier. "Cardboard is great for killing existing vegetation to create a garden bed," says horticulture extension specialist Aaron Steil. This process is called no-till or no-dig gardening, and it eliminates the need to remove existing vegetation to create a new garden bed. Not disturbing the soil protects important microorganisms and minimizes erosion. 

To do so, lay down a layer of brown corrugated cardboard where you want your garden bed to go. Water the cardboard, then top it with a layer of compost and water again. "To ensure water absorption, the mulch or compost atop the cardboard should be light enough to let the water penetrate down into the cardboard and soil layers," says garden author Jan Johnsen.

Prevent Weeds

Laying cardboard over the ground prevents sunlight from reaching weeds and keeps them from breaking through the soil surface. One downside to this method is that cardboard can be an eyesore when placed around the garden as a weed barrier. You can cover the cardboard with a layer of mulch to make it look more aesthetically pleasing, but this may cause the cardboard to break down faster.

Create Compost

Creating compost requires the correct ratio of carbon-rich and nitrogen-rich material. Adding cardboard to compost can boost its carbon content. "Green materials like grass clippings and food scraps are high in nitrogen," Steil says. "Brown materials like fallen leaves, straw, bark, and cardboard are high in carbon.” 

That said, don’t overdo it. Cardboard is very high in carbon (five times that of wood chips), so a little cardboard goes a long way in providing carbon to the compost pile, says Steil. Avoid waxed cardboard and remove any packing tape and staples, then shred it into smaller pieces before composting to speed up the decomposition process. 

Mistakes to Avoid

While cardboard can enhance your garden, there are some things to keep in mind.

• Don't use too much: Avoid using excessively thick layers of cardboard around established plants, Steil says. Doing so can restrict water and air movement to the soil, negatively affecting soil health and plant growth.
• Avoid waxed cardboard: Don't use glossy, shiny, or printed cardboard. "It may contain chemicals that aren’t ideal for your soil," says Johnsen. "Stick with plain brown corrugated cardboard."
• Not watering the cardboard: For no-dig gardening, soak the cardboard to aid in the decomposition process. "It's important to soak the cardboard well to help it begin breaking down," says Johnsen. "Cover the cardboard with 4 to 6 inches of compost, mulch, or a mix of both."