Is It OK to Put Cardboard Under Mulch?


Benefits and Drawbacks of Cardboard Mulch

It is acceptable to place cardboard under mulch as part of a gardening practice known as sheet mulching. This eco-friendly method can benefit your garden by suppressing weeds and improving soil health. However, there are also potential drawbacks to consider.


  • Weed Suppression: Cardboard serves as an effective weed barrier, limiting light exposure to the soil and suppressing weed germination and growth.
  • Soil Health: As cardboard decomposes, it contributes to the organic matter in the soil, promoting the activity of beneficial microorganisms and enhancing soil structure.
  • Eco-Friendly: Utilizing cardboard as mulch is a form of recycling that reduces waste and avoids the need for synthetic weed barriers such as landscaping fabric.


  • Decomposition Rate: The rate at which cardboard decomposes can vary, sometimes slowing down the process of adding nutrients back to the soil.
  • Soil Oxygenation: Thick layers of cardboard may impede the flow of oxygen to the soil, potentially affecting plant roots’ respiration and water absorption.
  • Toxicity Concerns: Some cardboard, particularly that which is coloured or glossy, may contain chemicals or dyes that could be harmful to the soil and plants.

When selecting cardboard for mulch, opt for plain, corrugated cardboard without glossy finishes and remove any staples or tape to avoid contamination. Layering your cardboard with organic mulch on top can create a more effective and aesthetically pleasing result, contributing to a balanced and healthy garden ecosystem. Always ensure to maintain sufficient moisture levels to support the decomposition of the cardboard and promote a thriving microorganism population in the soil.

Preparing the Garden for Cardboard Mulching

To effectively prepare your garden for cardboard mulching, start by clearing the area of large weeds, grass, and any undesired plants. If you’re dealing with perennial weeds or grass, ensure you remove as much of the root system as possible to prevent them from re-emerging.

Once you have cleared the vegetation, it’s time to lay down the cardboard. You should use large, flattened boxes and remove any tape, staples, or labels, as these do not break down and could interfere with the mulching process. Overlap the edges of the cardboard by at least 15 cm to create a continuous barrier that will deter weed and grass growth.

Before placing mulch on top of the cardboard, wetting it with a hose will aid in its decomposition and also keep it in place. This step is crucial as it allows for better adhesion of the organic mulch layer that will go on top and preserves the oxygen exchange necessary for soil and plant health.

Now, apply a generous layer of organic mulch over the cardboard. This could be compost, leaves, grass clippings, hay or even coffee grounds. Aim for a layer that’s about 10-15 cm thick to adequately suppress weeds and retain moisture in the soil.

In areas where you intend to plant, cut an X through the cardboard and fold back the flaps to create planting holes. Fill these with a mix of soil and compost, careful not to disrupt the cardboard’s position.

Finally, for garden paths or around landscape features like stones or rocks, consider placing a thicker layer of mulch or using heavier materials such as bark chips or stone to prevent displacement and maintain a neat appearance.

For gardeners interested in encouraging beneficial insects and worms, consider adding a thin layer of newspaper under the cardboard for extra insulation and decomposition material, which will enhance the habitat.

Remember, the key to successful cardboard mulching is ensuring full coverage and adequate moisture — this creates a hospitable environment for worms while deterring unwanted plant growth.

Best Practices in Cardboard Mulch Application

When using cardboard as a mulch underlayer in your landscape, you should follow certain best practices to ensure that the cardboard effectively suppresses weeds without harming your plants.


  • Source flat, clean cardboard without glossy prints or heavy inks.
  • Remove all tape and staples to avoid contamination.

Application Steps:

  1. Layout: Lay cardboard on the soil, ensuring pieces overlap by at least 15 cm to prevent weed growth through gaps.
  2. Moisten: Slightly wet the cardboard to help it conform to the soil surface and speed up decomposition.

Mulch Layering:

  • Once the cardboard is down, apply a thick layer (at least 10 cm) of organic mulch such as wood chips or compost over it.

Considerations for Plants:

  • Transplant: When planting, cut a hole in the cardboard for your plants, providing ample space for the root ball.
  • Reserve the use of cardboard mulch around established, native plants that can benefit from this added weed barrier.

Perennial Areas:

  • Be mindful of perennials and bulbs. Cardboard could potentially hinder their emergence. It’s best applied in areas designated for annuals or areas where you plan no plantings.


  • Regularly check the mulched area, adding more mulch as necessary to maintain its efficacy.
  • Monitor the moisture levels; you want to retain soil hydration without creating waterlogged conditions.

By adhering to these guidelines, you’ll create a natural, breathable barrier that effectively suppresses weeds and contributes to the health of your landscape.

Maintaining and Refreshing Cardboard Mulch

When implementing cardboard as mulch in your landscape, it’s essential to manage it effectively to reap the full benefits. Here are several key steps you should take to ensure your cardboard mulch remains effective:

Laying the Cardboard

  • Before mulching, lay flattened cardboard directly on the soil.
  • Ensure the cardboard overlaps by at least 15 cm to prevent weeds from finding an opening.
  • Soak the cardboard with water to aid in decomposition and help it conform to the ground.

Adding Mulch

  • Apply a layer of organic mulch on top of the cardboard. Aim for a layer 5-10 cm thick for optimal weed suppression and moisture retention.


  • Cardboard mulch should be kept moist but not waterlogged. Use a hose to gently water the area, especially during dry periods to maintain the moisture levels necessary for cardboard decomposition and soil health.

Monitoring for Pests

  • Regularly inspect your mulch for signs of slugs or other animals that might be attracted to the moist environment.

Assessing Plant Growth

  • Watch for the growth of native plants or fruit trees around the mulch. Ensure they have ample room and that the cardboard isn’t restricting their development.

Seasonal Refresh

  • Check the mulch’s condition in each season. Replace it when you notice significant breakdown or if weeds begin to penetrate.

Encouraging Earthworm Activity

  • Earthworms are beneficial to soil health. The decaying cardboard and mulch are likely to attract these creatures, which further helps to break down the mulch and enrich the soil.

Considering Oxygen Flow and Drainage

  • Be mindful that too thick of a cardboard layer might impede oxygen flow. Balance is key to maintain healthy soil aeration.

Remember, regular monitoring and maintenance of your mulched landscape will ensure the best results.

Impact on Plant and Soil Health

When you utilise cardboard as mulch in your garden, you’re adopting an eco-friendly approach that can have numerous positive effects on plant and soil health. Properly implemented, cardboard mulching can enhance the soil’s structure and fertility, leading to a more productive vegetable garden.

Benefits for Soil:

  • Moisture Retention: Cardboard helps the soil retain moisture, reducing the need for frequent watering.
  • Weed Suppression: It acts as a barrier, preventing weeds from getting the sunlight they need to grow.
  • Improvement of Soil Health: As the cardboard decomposes, it contributes valuable organic matter to the soil.

Benefits for Earthworms and Microorganisms:

  • Habitat: The cardboard mulch provides a favourable habitat for earthworms and beneficial microorganisms.
  • Food Source: Decomposing cardboard becomes food for earthworms and microorganisms which helps to aerate the soil and improve nutrient availability.

Considerations for Usage:

  1. Carbon to Nitrogen Ratio: Cardboard introduces carbon into your compost. Balance it with nitrogen-rich materials like grass clippings or green kitchen waste.
  2. Layering: Ensure cardboard is layered under other mulches, such as shredded leaves, to aid in its breakdown and integration into the soil.
  3. Avoid Glossy Cardboard: Stick to plain, non-coated cardboard to prevent introducing harmful chemicals into your garden.

By integrating cardboard into your mulching practices, you are not only contributing an organic material to your garden’s ecosystem but also supporting a cycle of growth that can improve the overall yield and health of your plants.

Frequently Asked Questions

Explore the most common inquiries about using cardboard as a layer beneath your garden mulch to ensure both successful application and understanding of this gardening practice.

What are the benefits and drawbacks of using cardboard as a mulching material?

When you use cardboard as a mulching material, you benefit from its excellent weed suppression capabilities and its role in improving soil health by retaining moisture and contributing to soil structure as it breaks down. One drawback, however, is that improper use can create a barrier that prevents water and nutrients from penetrating the soil.

Will cardboard used beneath mulch lead to an increase in termite activity?

There’s no conclusive evidence that cardboard beneath mulch significantly increases termite activity. However, you should monitor the mulched area because cardboard can provide an attractive habitat for termites due to its cellulose content.

How effective is cardboard at suppressing weeds when placed beneath mulch?

Cardboard is highly effective at suppressing weeds. By blocking sunlight and forming a physical barrier, it prevents weed germination and growth when place beneath a layer of mulch.

Is it safe to use cardboard around trees when applying mulch?

It’s safe to use cardboard around trees as long as you leave space around the tree trunk to prevent moisture buildup and potential rot. Apply the cardboard in a donut shape, not directly against the tree bark.

What types of cardboard are suitable for use in gardening contexts, such as allotments?

For your allotment, use plain, untreated cardboard without glossy finishes, heavy dyes, or adhesives. This ensures that no harmful chemicals leach into the soil as the cardboard decomposes.

Can applying cardboard before mulching offer a long-term solution for weed control?

Using cardboard under mulch can provide a long-term weed control solution as part of an integrated management system. For prolonged benefits, replace the cardboard once it has decomposed and before weeds manage to re-establish.

About the author 


Hey there, I am founder and editor in chief here at Good Grow. I guess I've always known I was going to be a gardener. I'm on a mission to share my UK based weed control & lawn care tips with you all. If you have any queries please post in the comments below.

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