What Do I Put On The Bottom Of A Raised Garden Bed? (The Ultimate Guide)

You’ve built it. That beautiful, sturdy raised garden bed is sitting proudly in your yard, a blank canvas of potential. You’re ready to fill it with soil, plant your seeds, and watch your garden paradise grow. But then, a moment of hesitation hits: What on earth do I put on the bottom of this thing?

This isn’t just a minor detail. What you place—or don’t place—at the base of your raised bed is one of the most critical decisions you’ll make. Get it right, and you lay the foundation for thriving plants with incredible yields and robust health. Get it wrong, and you could be battling drainage issues, hungry pests, and root rot for seasons to come.

Forget the conflicting advice from well-meaning neighbors and confusing online forums. This definitive guide cuts through the noise. We’ll explore the pros and cons of every option, from hardware cloth to cardboard, so you can make an informed decision that ensures your raised bed garden becomes the envy of the neighborhood.

The Short Answer: It Depends (But Here’s the TL;DR)

Before we dive deep, let’s address the most common question directly. For the vast majority of gardeners, the best thing to put on the bottom of a raised garden bed is a single layer of hardware cloth (a sturdy, galvanized wire mesh) covered with a layer of cardboard or a biodegradable landscape fabric.

• The hardware cloth acts as an impenetrable barrier against burrowing pests like voles, gophers, and moles.
• The cardboard or fabric suppresses weeds from below while still allowing for water permeability and soil breathability.

This combination tackles the two biggest concerns—pests and weeds—without creating the drainage nightmares associated with other materials. Now, let’s unpack why this is the gold standard and explore all the other options in detail.

The Primary Goal: Understanding Your “Why”

Before choosing a material, you must understand the core functions of your raised bed’s foundation. It’s not a one-size-fits-all scenario. Your choice should be based on your specific environment and challenges.

1. Weed Suppression: Preventing perennial weeds and grass from growing up into your precious garden soil.
2. Pest Control: Deterring burrowing rodents from feasting on your plant roots and bulbs.
3. Drainage: Allowing excess water to escape freely to prevent waterlogged soil and root rot.
4. Soil Retention: Keeping your expensive garden soil from washing out through the bottom while still allowing roots to penetrate deeper if desired.
5. Separation: Creating a barrier between your clean soil and potentially contaminated native soil below (a key consideration for urban gardening).

Option 1: The Champion Duo – Hardware Cloth & Cardboard

This is our recommended, all-star combination for a reason.

Hardware Cloth:

• What it is: A mesh made of galvanized steel, typically sold in rolls with a grid pattern (½ inch is a great size).
• Pros: Provides an unbeatable physical barrier against digging pests. It’s durable, long-lasting, and won’t decompose.
• Cons: Adds a small upfront cost and requires wire cutters to size.
• How to use: Staple or tack it directly to the bottom of your wooden raised bed frame before you place it on the ground. If the bed is already in place, you can lay it directly on the soil underneath.

Cardboard (or Newspaper):

• What it is: Plain brown cardboard (remove all tape and glossy labels) or a thick layer of newspaper.
• Pros: Excellent for weed suppression. It smothers existing grass and weeds, which will eventually decompose and add organic matter to the soil. It’s free, biodegradable, and allows water and air to pass through.
• Cons: It will break down over one or two seasons, so it’s not a permanent solution for aggressive weeds like Bermuda grass.
• How to use: Lay a single layer over the hardware cloth (or directly on the ground if pests aren’t a concern). Wet it down thoroughly to help it conform to the shape of the ground and begin the decomposition process.

Option 2: The Simple & Effective – Cardboard Alone

If you don’t have a significant issue with burrowing animals, using just a thick layer of cardboard is a fantastic, no-cost option. It’s the go-to choice for many organic gardeners practicing lasagna gardening or sheet mulching techniques right in their raised beds.

This method is perfect for converting a grassy area directly into a garden. The cardboard kills the grass underneath, and by the time plant roots reach the bottom, it will have softened enough for them to push through into the native soil below, which can be beneficial for deep-rooted plants.

Option 3: The Controversial One – Landscape Fabric

Note: There is a huge difference between woven and non-woven landscape fabric. For raised beds, you only want a high-quality, permeable woven geotextile fabric.

• Pros: Provides longer-lasting weed control than cardboard. It’s water-permeable and allows for gas exchange.
• Cons (the important part): Cheap, non-woven fabrics can become clogged with soil particles over time, creating a waterproof barrier that causes drainage issues and prevents root penetration. It can also disrupt the natural ecosystem of worms and beneficial microbes moving between your raised bed soil and the earth.
• Verdict: If you use it, invest in a quality product. However, for most, cardboard is a more effective and natural choice.

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What About Drainage? The Gravel Layer Myth

This is perhaps the most persistent and damaging myth in raised bed gardening.

Do NOT put a layer of gravel, rocks, or sand at the bottom of your raised bed to improve drainage.

This seems counterintuitive, but it’s backed by basic soil science. Here’s why it’s a terrible idea:

1. The Perched Water Table Effect: When you place a layer of chunky material like gravel under a finer material like soil, you create a textural barrier. Water does not easily transition from fine soil to large pores in gravel. Instead of draining freely, the water will “perch” or pool in the soil layer right above the gravel, waterlogging your plants’ root zones—the exact opposite of your goal.
2. Wasted Depth and Money: Gravel is heavy and expensive. It takes up valuable vertical space that should be filled with nutrient-rich soil where your plants’ roots want to grow.
3. It Makes the Bed Heavier: A bed filled with soil is heavy enough. Adding hundreds of pounds of rock makes it immovable and puts more stress on the structure.

True drainage is achieved by having a well-aerated, fluffy soil mix itself, not by what’s underneath it. If you have severe clay soil, you might consider using your raised bed as more of a “container” and installing a few drainage holes in the sides just above the native ground level, but a gravel base is still not the solution.

Materials to Absolutely Avoid

Just as important as knowing what to use is knowing what to avoid. Never line the bottom of your bed with:

• Plastic Sheeting: This will create an impermeable barrier, leading to catastrophic drainage failure, root rot, and a suffocated, anaerobic soil environment.
• Pressure-Treated Wood (Old Formula): While modern pressure-treated lumber (labeled ACQ) is considered safe for gardens, the old stuff containing arsenic (CCA) is not. Never use old CCA wood as a liner or for building beds.
• Carpet: Old carpet can leach toxic chemicals and dyes into your soil and does not biodegrade properly.

Special Circumstances: When to Break the Rules

1. For a Bed on a Hard Surface (Patio, Pavement, Rooftop): If your bed is not on soil, you are essentially creating a giant planter. Drainage holes are mandatory. In this case, you still don’t need a gravel layer. Simply ensure there are adequate holes (½ to 1 inch) drilled every foot or so along the sides, about an inch or two up from the very bottom. Line the inside with a layer of cardboard to prevent soil from washing out before it establishes.
2. For a Bed Over Severely Contaminated Soil: If you have legitimate concerns about lead or other heavy metals in your native soil, you can use a heavy-duty landscape fabric as a more permanent barrier. However, for true peace of mind, building a deeper bed (24+ inches) and filling it entirely with clean soil is a better strategy, as roots are unlikely to reach the contaminated layer.

The Step-by-Step Guide to Prepping Your Raised Bed Bottom

1. Site Prep: Clear the area of large rocks and debris. If dealing with aggressive grass, you can mow it as short as possible.
2. Install Pest Barrier (If Needed): If voles or gophers are a concern, staple hardware cloth directly to the bottom of your empty bed frame.
3. Place the Bed: Position the framed and secured bed in its permanent location.
4. Lay Weed Barrier: Cover the entire ground surface inside the bed with overlapping sheets of untreated cardboard or newspaper. Remove any tape or labels. Soak it thoroughly with a hose.
5. Begin Filling: Now, you can start layering your soil and compost ingredients directly on top of the cardboard.

Beyond the Bottom: Don’t Forget the Soil!

Your perfectly prepped bottom is useless without the right stuff on top. The magic of a raised bed garden comes from the deep, loose, and fertile soil you put in it. Aim for a simple mix:

• 1/3 High-Quality Compost: Provides nutrients and microbial life.
• 1/3 Peat Moss or Coco Coir: Helps retain moisture and lighten the mix.
• 1/3 Vermiculite or Perlite: Aeration and moisture retention.

Many garden centers sell pre-mixed “raised bed soil,” which is a great convenient option.

Conclusion: Build a Strong Foundation for a Thriving Garden

The question of “what to put on the bottom” is fundamental. By choosing the right materials—primarily a combination of hardware cloth for pest control and cardboard for weed suppression—you aren’t just building a container for dirt. You are engineering a healthy, productive ecosystem from the ground up. You’re ensuring proper drainage, protecting your investment in plants and soil, and setting the stage for seasons of abundant harvests.

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