Introduction
When setting up a raised garden bed, many gardeners wonder if placing cardboard underneath is a good idea. This simple step can significantly influence soil health, weed control, and overall garden productivity. But is it really necessary? And if so, how should you do it?
In this article, we’ll explore the benefits and drawbacks of putting cardboard under raised garden beds. You’ll learn how cardboard works as a gardening tool, whether it’s suitable for your specific garden needs, and best practices to implement it effectively. Whether you’re a beginner or an experienced gardener, this guide will help you make an informed decision about using cardboard in your raised bed setup.
Why Consider Putting Cardboard Under Raised Garden Beds?
What Purpose Does Cardboard Serve?
Placing cardboard under raised beds primarily helps with:
- Weed suppression: Cardboard creates a barrier that blocks sunlight, preventing existing weeds and grass from growing through the soil.
- Soil improvement: As cardboard decomposes, it adds organic matter to the soil, enhancing moisture retention and nutrient content.
- Pest control: It can discourage some pests by creating a physical barrier between the ground and your garden bed.
- Cost-effective weed barrier: Compared to synthetic weed fabrics, cardboard is an affordable and eco-friendly option.
How Does Cardboard Compare to Other Weed Barriers?
Unlike plastic sheeting or landscape fabric, cardboard is biodegradable. This means it breaks down naturally over time, enriching the soil rather than creating a permanent barrier. However, cardboard’s durability is less than synthetic materials, requiring consideration of how long you want the barrier to last.
Should You Put Cardboard Under Your Raised Garden Bed? Key Factors to Consider
1. What Is Your Garden Bed Base?
Raised beds can be placed on:
- Grass or lawn: Cardboard is highly recommended here to smother grass and prevent roots from invading your bed.
- Bare soil or dirt: Cardboard can still be beneficial by suppressing weeds and improving soil structure.
- Concrete or paved surfaces: Cardboard is less effective and usually unnecessary, as no soil or weeds exist beneath.
2. What Type of Raised Bed Are You Using?
- Wooden frames: Cardboard works well and can be layered under the frame before adding soil.
- Metal or plastic beds: While still possible, be mindful that cardboard may retain moisture and cause faster rusting or degradation in some materials.
- No-frame/mounded beds: Cardboard can be laid directly on the ground before piling soil, acting as a sheet mulch.
3. How Long Do You Plan to Use the Raised Bed?
Since cardboard breaks down over months, it is ideal for short to medium-term weed control (1-3 years). If you want a permanent solution, combining cardboard with a more durable barrier might be necessary.
How to Properly Use Cardboard Under Raised Garden Beds
Step-by-Step Guide
- Clear the area: Remove large rocks, sticks, and debris from the site where you’ll place your raised bed.
- Lay down cardboard sheets: Use large, flat pieces of cardboard, overlapping edges by at least 6 inches to prevent gaps.
- Remove tape and labels: Any plastic tape, stickers, or glossy paper should be taken off to avoid introducing non-biodegradable materials.
- Wet the cardboard: Moisten it thoroughly to help it start decomposing and conform to the ground.
- Place the raised bed frame: Set your garden bed on top of the cardboard.
- Add soil and compost: Fill the bed with your growing medium, ensuring good contact with the cardboard layer below.
Tips for Best Results
- Use multiple layers of cardboard for thicker weed suppression.
- Avoid cardboard with heavy inks or coatings that may contain harmful chemicals.
- Incorporate organic matter like compost on top to speed up decomposition.
- Monitor moisture levels; cardboard can retain water, which is good for plants but may cause soggy conditions if overwatered.
Benefits of Using Cardboard Under Raised Garden Beds
- Effective weed control: Blocks weed growth by cutting off light.
- Improves soil health: Adds carbon-rich organic matter as it breaks down.
- Eco-friendly: Uses recycled materials and reduces plastic use.
- Cost-effective: Cardboard is often free or cheap to obtain.
- Enhances moisture retention: Helps keep soil moist longer by reducing evaporation.
Potential Drawbacks and How to Mitigate Them
| Potential Issue | Explanation | How to Mitigate |
|—————————–|——————————————–|————————————|
| Slower decomposition in dry or compacted soils | Cardboard may take longer to break down | Keep cardboard moist and aerate soil |
| Attracts pests like termites or rodents | Some pests might shelter under cardboard | Monitor regularly and avoid excess moisture |
| Can harbor mold or fungi | Excess moisture can promote fungal growth | Ensure proper drainage and airflow |
| Not suitable for concrete bases | Decomposition is irrelevant on hard surfaces | Skip cardboard or use other materials |
Expert Opinions on Using Cardboard Under Raised Beds
Dr. Emily Stone, Soil Scientist:
“Cardboard is an excellent biodegradable weed barrier that also contributes to soil organic matter. It’s especially useful for gardeners seeking sustainable practices.”
John Peterson, Urban Gardening Specialist:
“I always recommend cardboard under raised beds on grass or lawn areas. It reduces maintenance and improves soil health without the environmental downsides of plastic.”
Frequently Asked Questions (FAQs)
Can I use cardboard with landscape fabric?
Yes, you can combine cardboard with landscape fabric for longer-lasting weed control. Place cardboard first for organic matter and fabric on top for durability.
How long does cardboard last under a raised bed?
Typically, cardboard decomposes within 6 months to 2 years, depending on moisture, temperature, and soil activity.
Is cardboard safe around edible plants?
Uncoated and ink-free cardboard is safe. Avoid glossy or colored cardboard that may contain harmful chemicals.
Will cardboard affect soil drainage?
Cardboard is porous and generally does not impede drainage but monitor soil moisture to avoid sogginess.
Conclusion
Placing cardboard under your raised garden bed is a practical, eco-friendly method to suppress weeds, improve soil health, and retain moisture. It works best on grass or bare soil and suits gardeners aiming for sustainable, chemical-free solutions. While it decomposes over time and may require occasional replacement, cardboard offers a cost-effective and accessible option for enhancing your garden’s productivity.
Before laying cardboard, consider your garden bed type, base surface, and long-term plans to ensure it aligns with your gardening goals. With proper preparation and maintenance, cardboard can be a valuable ally in creating a thriving raised garden bed.
Ready to start your raised garden bed project? Grab some cardboard and see the benefits in your garden firsthand—your plants will thank you!
