Yes, cardboard under mulch is a highly effective and widely recommended method for weed suppression, soil improvement, and moisture retention in gardening and landscaping. This technique leverages the natural decomposition of cardboard to create a chemical-free weed barrier while enriching the soil beneath.
How Cardboard Under Mulch Functions
The core principle behind using cardboard beneath mulch is sheet mulching or lasagna gardening. When applied, cardboard serves as an initial barrier, effectively smothering existing weeds and grasses by blocking sunlight and air. This non-chemical approach allows gardeners to clear very large areas of unwanted vegetation without relying on synthetic herbicides.
- Weed Suppression: Cardboard, especially corrugated types, forms a dense layer that deprives weeds and grass of the light they need to grow, causing them to die back. This is particularly useful for establishing new garden beds or reclaiming overgrown areas.
- Moisture Retention: The cardboard layer helps to retain soil moisture by reducing evaporation. This means less frequent watering is needed, which is beneficial for plants and water conservation.
- Soil Improvement: As the cardboard breaks down over time, it adds organic matter to the soil. This process enhances soil structure, aeration, and fertility, creating a highly fertile site that supports beneficial microorganisms and earthworms. This decomposition also contributes to a healthier root environment for desired plants.
- Chemical-Free Solution: One of the most significant advantages is eliminating the need for synthetic weed killers, promoting a more organic and environmentally friendly gardening practice.
Benefits of Using Cardboard Under Mulch
Using cardboard in your garden offers a range of practical advantages:
- Eco-Friendly: Reduces chemical use and recycles cardboard waste.
- Cost-Effective: Often uses readily available and free materials.
- Enhanced Soil Health: Improves soil structure, water infiltration, and nutrient availability.
- Reduced Weeding: Significantly cuts down on manual weeding efforts over time.
- Temperature Regulation: Helps moderate soil temperature, protecting plant roots from extreme heat or cold.
How to Apply Cardboard for Best Results
For optimal effectiveness, follow these steps when laying cardboard under mulch:
- Prepare the Area: Clear any large debris, but it's not necessary to remove existing weeds or grass, as the cardboard will smother them.
- Lay Cardboard:
- Use plain, un-waxed corrugated cardboard. Remove all tape, labels, and staples.
- Overlap the edges of the cardboard by at least 6-8 inches (15-20 cm) to prevent weeds from growing through the seams.
- Make sure to cut holes or leave space around existing plants if you are not starting a new bed.
- Wet the Cardboard: Thoroughly wet the cardboard layer with water. This helps it settle, conform to the ground, and begin the decomposition process. It also prevents it from blowing away.
- Apply Mulch: Immediately cover the wetted cardboard with a 3-6 inch (7.5-15 cm) layer of organic mulch. Good options include wood chips, shredded bark, straw, or compost. This layer holds the cardboard in place, improves aesthetics, and provides additional benefits.
- Layering Materials: For creating a particularly fertile site, a gardener may put several layers of materials. This could involve alternating layers of cardboard, compost, and other organic matter before applying the final mulch layer.
Considerations for Cardboard Use
| Aspect | Description |
|---|---|
| Type | Use plain, brown, un-waxed corrugated cardboard. Avoid glossy, colored, or heavily printed cardboard. |
| Thickness | Thicker cardboard offers better weed suppression but takes longer to decompose. |
| Drainage | Ensure proper drainage; excessive cardboard layers can sometimes temporarily impede water penetration. |
| Longevity | Cardboard typically breaks down within 6-12 months, requiring reapplication or addition of more mulch. |
Related Resources
- For more on the benefits of mulching in general, explore resources from cooperative extensions like the University of Maryland Extension.
- Understand different types of organic mulches and their uses through guides from institutions like Oregon State University Extension.
Using cardboard under mulch is a highly effective, organic strategy for maintaining a healthy, weed-free garden while simultaneously building rich, fertile soil.
