Should you use cardboard in the landscape?
It depends. Many of us receive deliveries from online sources and have access to plenty of cardboard, and nobody likes to pull weeds for hours. Plus, there are some pervasive weeds out there that can be very difficult to control. The bottom line is that sometimes cardboard can be an effective tool.
Placing a layer of cardboard over lawn areas and weeds is effective at killing off most vegetation when establishing a new landscape planting.
How Does Cardboard Help with Weed Control?
Blocking Light to Kill Weeds
Placing a layer of cardboard over lawn areas and weeds is effective at killing off most vegetation when establishing a new landscape planting. Cardboard works because it blocks the light that the unwanted plant needs for photosynthesis.
Preventing Weed Seeds from Germinating
Also, most weed seeds need soil contact to germinate, so future weed numbers are also reduced. Use sod staples to anchor the cardboard and an additional three inch layer of medium to coarse mulch to prevent new weeds from growing. The top inch of a medium to coarse mulch, like pine straw or large bark chips, works better than finer mulches at hindering germination of weed seeds.
What Are the Benefits of Using Cardboard for Soil Fertility?
Cardboard is mostly carbon, and carbon is a necessary nutrient easily derived from the atmosphere.
Nitrogen and Compost Are Important for Decomposing Cardboard
Cardboard will need some nitrogen from the soil, or even better, some compost, to help it break down in the environment, which can take four to six months.
If you want to build soil fertility, add organic matter. HGIC Factsheet 1655 Soil Conditioning – Establishing a Successful Gardening Foundation covers many options for adding organic matter to native soils.
How to Use Cardboard for Weed Control and Bed Preparation
Cardboard can be very effective in helping to create landscape beds and limit the need to till, but keep in mind you need to keep it moist. Cardboard boxes are hydrophobic to a certain degree, and if allowed to dry out, they can prohibit water from reaching plant roots. This can be critical during establishment periods for larger trees and shrubs and detrimental when we have extended dry periods.
Cardboard boxes are hydrophobic to a certain degree, and if allowed to dry out, they can prohibit water from reaching plant roots.
Jackie Jordan, ©2025, Clemson Extension
In established landscape beds, it is best to stick to just a three-inch layer of mulch. More options for mulch can be found in HGIC Factsheet 1604 Mulch.
Sod staples and an additional layer of mulch are needed to anchor the cardboard and prevent new weeds from growing.
Jackie Jordan, ©2025, Clemson Extension
Does Cardboard Affect Soil Oxygen and Microbial Populations?
I don’t know if enough research has been done to look at the effect of cardboard on various soil types and long-term effects. Tilling has been shown to harm microorganisms, destroy soil structure, and lead to soil compaction in soil layers below the tilled soil.
I do know soil oxygen can be improved, and the population of microorganisms can be increased in native soils through the addition of organic matter. We live in a hot, humid climate, and our South Carolina gardens should receive regular applications of organic matter to keep the soil healthy and productive. I tend to think of soil as being in a continual building process, not once and done. Every year, I mulch my grass clippings, add compost to my vegetable gardens, and add mulch to my landscape beds.
Are There Chemicals in the Cardboard to Avoid Using in the Garden?
• Glue: The glue used to hold the cardboard layers together is made from plant starches. The glue used on the seams of heavy-duty boxes can contain chemicals, so avoid those boxes or remove those parts before using them in the garden.
• Ink: The black ink used on boxes is made from vegetable-based dye. The colorful ink on boxes can contain heavy metals, so avoid using those boxes.
• Tape/Labels: The tape and labels should also be removed because they contain plastic.
Final Thoughts on Cardboard in the Garden
Cardboard should be thought of as another tool in the gardener’s toolbox. It can be an effective tool when establishing a new garden bed, but there are better soil building and mulching practices that ensure long term plant health.
