What to Put Under a Raised Bed: A Practical Guide

You’ve built the raised bed. It’s sitting exactly where you want it. The soil is ready to go in. Then comes one last question:

Should I put something underneath it first?

Cardboard? Hardware cloth? Nothing at all? There isn’t one bottom setup that every raised bed needs. What goes underneath depends on what the bed is sitting on—and what you’re trying to keep out.

A bed going over a lawn has different needs from one sitting on pavers. And if gophers or voles are already part of your garden, that changes the setup again.

So before you start filling, take a look down.

Use the guide above as a starting point. Once you know what belongs underneath your bed, the next step is installing it correctly.

Using Cardboard? Do These 4 Things First

Cardboard is simple, inexpensive, and useful when you want to suppress existing grass or weeds underneath a new raised bed.

But there are a few things worth doing before the soil goes in.

1. Keep It Plain

Use plain, uncoated cardboard.

Remove plastic shipping tape, labels, staples, and other synthetic materials before putting it in the garden. I’d also skip heavily coated or waxed cardboard. You don’t need a special type of cardboard. Clean shipping boxes are usually all you need.

2. Overlap the Sheets

Don’t lay the cardboard edge to edge like floor tiles.

Overlap the sheets so there aren’t obvious gaps between them. Existing grass and weeds are very good at finding whatever little opening you leave behind. If the cardboard shifts while you’re working, straighten it out before moving on.

3. Wet It Thoroughly

Don’t put dry cardboard down and immediately bury it under soil.

A dry sheet can temporarily slow or redirect water instead of letting moisture move evenly into the ground below. And if cardboard is allowed to dry out later, it can become harder for water to penetrate.

Once the sheets are in place, soak them thoroughly with water. This helps the cardboard settle against the ground, keeps it from shifting while you fill the bed, and gives decomposition a head start.

4. Fill the Bed

One important reminder: cardboard is useful for suppressing existing vegetation, but it isn’t magic. If you’re dealing with aggressive perennial weeds such as Bermuda grass, bindweed, or quackgrass, remove or control as much as possible before covering the area.

Using Hardware Cloth? Get the Edges Right

If gophers or voles are a known problem in your garden, galvanized hardware cloth can create a physical barrier between the raised bed and the ground underneath. And this is definitely a job I’d rather do while the bed is empty.

Start with sturdy galvanized hardware cloth with a small mesh opening, such as 1/4 inch.

Cover the entire bottom of the raised bed rather than just the center. A barrier doesn’t help much if a burrowing animal can simply find its way around the edge.

Then pay close attention to the perimeter. Fit and secure the hardware cloth around the bottom edges so you don’t leave obvious openings.

With hardware cloth, the edges matter as much as the mesh.

Be careful when cutting it, too. Freshly cut metal mesh can leave sharp wire ends, so wear gloves while working and make sure cut edges are safely positioned or secured before filling the bed.

If you also need to suppress grass or weeds, the order is simple:

Hardware cloth first → Cardboard on top → Wet the cardboard → Add soil.

A Quick Note About Concrete and Pavers

If your raised bed is sitting on concrete, a patio, or pavers, weed suppression usually isn’t the main concern.

Drainage is.

Make sure water has a clear way to leave the bed and think about where that water will go once it drains out. You’ll also want enough soil depth for the crops you plan to grow, since roots can’t simply continue down into the ground below.

Before You Fill

Once a raised bed is full of soil, changing what’s underneath becomes a much bigger job. So take a minute before you fill it.

Look at the ground, figure out what problem you’re actually trying to solve, and use the bottom setup that makes sense for your garden. Then get the soil in and start growing.

Happy growing. 🌱

Should You Line the Bottom of a Raised Bed? Here’s What to Use