What To Put At Bottom Of Raised Garden Bed

If you’re building a raised garden bed, knowing what to put at the bottom is essential for healthy growth. Getting this foundational layer right sets the stage for everything that follows, from strong roots to bountiful harvests. It’s a common question with a suprisingly important answer. The wrong choice can lead to drainage problems or compacted soil, while the right one creates a thriving ecosystem for your plants.

Let’s break down your options, from the best materials to use to the ones you should absolutely avoid. We’ll make sure your garden gets the best possible start.

Your main goal for the bottom layer is to improve drainage while blocking persistent weeds. You want water to flow freely so plant roots don’t sit in soggy soil, which causes rot. At the same time, you need a barrier against grass and weeds from below that might try to invade your nice new bed.

The Best Materials for the Bottom Layer

These are the top choices that most gardeners rely on. They are effective, affordable, and easy to find.

Hardware Cloth or Galvanized Wire Mesh: This is your first line of defence against burrowing pests like voles, gophers, and moles. Staple or tack it directly to the bottom of your bed frame before adding anything else. It’s a crucial step many people forget.
Cardboard or Newspaper: A thick layer of plain cardboard (remove tape and stickers) or 10-15 sheets of newspaper is fantastic. It smothers existing grass and weeds, eventually breaking down to add organic matter. It allows water and worms to pass through while blocking light.
Landscape Fabric (Weed Barrier): A permeable geotextile fabric is a good option. It lets water drain out but prevents weeds from coming up. Ensure it’s a quality fabric; cheap plastic can clog and cause drainage issues.
Sticks, Logs, and Brush (The “Hugelkultur” Method): For deep beds, placing a base of rotting wood, branches, and leaves is brilliant. As the wood decomposes, it retains moisture, provides nutrients slowly, and creates air pockets. It also saves you money on soil!

Materials to Use With Caution

Some common suggestions need careful consideration or specific situations to work well.

Gravel or Rocks: A thin layer of small rocks can aid drainage, but a thick layer can create a “perched water table,” where water actually pools above the rocks. It also makes the bed very heavy. Best used sparingly if at all.
Sand: Mixed into your soil, sand improves drainage. But a thick layer at the bottom can compact and harden, creating a barrier that’s worse than the problem you’re trying to solve.
Leaves and Grass Clippings: These are great as part of a layered approach, but on their own they will mat down and decompose quickly, leading to settling. Mix them with brown materials like straw or use them above a cardboard layer.

What You Should Never Put on the Bottom

Avoid these materials at all costs. They will cause more problems than they solve and can harm your plants.

Plastic Sheeting or Tarps: This is a major mistake. Plastic creates an impermeable barrier that traps water, leading to root rot and drowned plants. It also prevents worms and beneficial microbes from moving into your bed from the native soil.
Pool Liner or Rubber Mats: For the same reasons as plastic, these materials prevent proper drainage and gas exchange. Your garden bed will essentially become a sealed container, which is not ideal for most vegetables.
Fresh Wood Chips or Sawdust: Placed at the bottom, these will rob nitrogen from your soil as they decompose, starving your plants. They are better used as a top-layer mulch after your plants are established.

Step-by-Step Guide to Layering Your Raised Bed

Here is a simple, effective method to build your raised bed from the ground up. This lasagna-style layering creates a rich, fertile environment.

Site Preparation: Clear the area of major weeds and grass. Loosen the top few inches of the native soil with a garden fork to improve integration.
Install Pest Barrier: If pests are a concern in your area, staple hardware cloth to the entire bottom of the bed frame.
Add Weed Block Layer: Lay down cardboard or newspaper directly over the grass, overlapping the edges well. Water it thoroughly to help it start breaking down and stay in place.
Add Bulk Organic Matter (Optional for deep beds): For beds over 18 inches deep, add a layer of small logs, sticks, or coarse brush. This is your hugelkultur base.
Layer Brown and Green Materials: Add alternating layers of carbon-rich “browns” (straw, dried leaves, shredded paper) and nitrogen-rich “greens” (grass clippings, vegetable scraps, coffee grounds). Moisten each layer as you go.
Top with Quality Soil Mix: Fill the final 12-18 inches with a premium soil mix. A classic recipe is 1/3 compost, 1/3 topsoil, and 1/3 aeration material like coconut coir or peat moss.

Common Mistakes to Avoid

Even with the right materials, a few errors can undermine your efforts. Keep an eye out for these pitfalls.

Compacting the Layers: Avoid walking on or heavily pressing down your layers, especialy the soil. You want it loose and fluffy for root growth.
Using Contaminated Materials: Never use pressure-treated wood from before 2003, painted wood, or cardboard with glossy, colored ink in your garden. They can leach harmful chemicals.
Neglecting Soil Depth: Most vegetables need at least 12 inches of good soil. Ensure your final soil layer, not including the bottom fillers, meets this minimum.
Forgetting to Water the Layers: When building, dry layers will wick moisture away from your plants. Dampening each layer as you build helps everything settle and start decomposing.

FAQ: Bottom of Raised Garden Bed

Do I need to line the bottom of a raised bed?

It’s highly recommended. A lining of cardboard or landscape fabric suppresses weeds and improves the bed’s function. Without it, grass and weeds will grow up into your soil.

Should I put drainage holes in my raised bed?

If your bed has a solid bottom (like on a patio), then yes, you must drill holes. If it’s open-bottomed and sitting on soil, the holes are not necessary—drainage happens through the soil interface.

Can I just fill my bed with bagged soil?

You can, but it’s expensive for deep beds. Using a layered approach with organic fillers at the bottom saves money and creates a richer, more resilient soil ecosystem over time.

How do I keep weeds from growing up from the bottom?

A thick, overlapping layer of plain cardboard is the most effective and natural method. It blocks light and smothers weeds, eventually decomposing harmlessly.

What is the cheapest thing to put in the bottom of a raised garden bed?

Cardboard from old boxes is free and very effective. Fall leaves, sticks, and logs from your yard are also excellent no-cost options for adding bulk and nutrients.

Choosing what to put at the bottom of your raised garden bed is a simple decision with long-lasting effects. By starting with a good pest barrier, a weed-smothering layer like cardboard, and perhaps some rotting wood for moisture retention, you build a foundation that supports healthy growth for seasons to come. Remember to avoid solid barriers like plastic and focus on materials that allow life—both water and soil organisms—to move freely. With this setup, your plants will have the deep, well-drained, and fertile environment they need to thrive. Now you’re ready to fill the rest of your bed and get planting.