Setup
What Goes in the Bottom of a Raised Garden Bed
Most raised beds need no solid bottom at all. Lay plain cardboard over grass to smother it, add hardware cloth if gophers or voles dig, and skip gravel.
| Option | Use it when | Lasts | Notes |
|---|---|---|---|
| Nothing | Bed sits on loosened, weed-free soil | Not applicable | Roots and worms move freely |
| Cardboard | Bed sits on lawn or weeds | A few months | Remove tape and glossy labels |
| Newspaper | Light weeds, small beds | A few months | Use 6 to 10 sheets, black ink only |
| Hardware cloth | Gophers, moles or voles | Several years | Half-inch galvanized mesh |
| Logs and branches | Beds 18 inches or deeper | Several years | Soil sinks as wood rots |
| Landscape fabric | Bed sits on gravel or pavers | Several years | Blocks roots and worms; skip on soil |
Do you need a bottom at all?
For a bed sitting on the ground, usually not. An open bottom lets excess water drain into the soil below, lets roots go deeper than the frame, and lets earthworms move up into the bed. A solid floor of plywood or plastic turns the bed into a big container that stays soggy after rain.
Three situations change that. If the bed sits on lawn or weeds, you need something to smother them. If gophers or voles are common in your area, you need a barrier they can't chew through. And if the bed is very deep, you may want to fill the lower part with something cheaper than soil.
Beds on a patio or driveway are their own case. There's nothing to smother, but soil can wash out from under the boards. A layer of landscape fabric under the frame holds soil in while letting water through. Make those beds at least 12 inches deep, since roots can't reach anything below. Beds on legs always have a built-in floor with drainage holes; see elevated raised garden beds for those.
Cardboard and newspaper
Cardboard is the simplest way to start a bed on top of grass. Mow the grass short, lay plain brown cardboard over the whole footprint, and overlap the edges by 6 inches so nothing pokes through the seams. Peel off plastic tape, shipping labels and glossy printed sections first.
Wet it thoroughly before adding soil. Damp cardboard softens and molds to the ground, and it breaks down in a few months, by which point the grass underneath is dead.
Newspaper does the same job in a thinner layer. Use 6 to 10 sheets of black-and-white newsprint and overlap generously. It breaks down faster than cardboard, so it's better for lawn grass than for tough weeds like bermudagrass or bindweed. For those, use two layers of cardboard, or dig out the roots first.
Hardware cloth for gophers
If you've seen gopher mounds or vole runways in your yard, line the bottom before you fill.
Use galvanized hardware cloth with half-inch openings, which is welded mesh rather than chicken wire. Chicken wire rusts through quickly and gophers can squeeze through its larger holes. Cut the mesh a few inches larger than the bed on every side. Lay it flat on the leveled ground, bend the edges up 2 to 3 inches inside the frame, and staple or screw them to the boards so there's no gap at the corners.
Hardware cloth lasts several years in the ground, depending on soil moisture. Roots grow through the openings without trouble. Over grass, lay mesh first and cardboard on top. You'll find the framing and fastening steps in how to build a raised garden bed.
Logs and branches
Filling the bottom of a deep bed with wood is a version of hugelkultur. Rotting logs hold water like a sponge and slowly feed the soil above. They also cut the amount of soil you have to buy.
Use it only in beds 18 inches or deeper, and keep the wood in the bottom third. Big logs go down first, then branches, then twigs, then a few inches of leaves to fill the gaps. Soak each layer. Top with at least 10 to 12 inches of real soil mix so roots have something to grow in while the wood breaks down.
Expect the surface to sink several inches over the first couple of years as the wood rots, and plan to top it up. Hardwoods like oak and maple last longer than softwoods. Leave out black walnut, which releases a compound that harms tomatoes and many other vegetables, and any treated, painted or stained lumber.
What not to put in the bottom
- Gravel or rocks. It seems logical for drainage, but water won't move from fine soil into coarse gravel until the soil above is saturated. The result is a wetter root zone, not a drier one.
- Plastic sheeting under the soil. It traps water and blocks roots.
- Treated wood scraps, railroad ties and painted lumber. They can leach chemicals into the soil you grow food in.
- Black walnut wood, leaves or hulls.
- Pallets and plywood of unknown origin. Some are chemically treated, and a solid wood floor stays wet.
- Glossy or heavily printed cardboard, foam, packing peanuts or other trash used as filler.
Once the base is down, move on to the soil. Our guide to cheap layering covers the middle of the bed, and the soil mix recipe covers the top layer roots actually use.
How to choose
Bed on lawn
Cardboard, wetted down, under the whole footprint. No other bottom is needed.
Gophers or voles nearby
Half-inch hardware cloth fastened to the frame, with cardboard on top if there's grass.
Bed deeper than 18 inches
Logs and branches in the bottom third, then at least 10 inches of soil mix.
Bed on concrete or pavers
Landscape fabric under the frame, at least 12 inches of soil, and no solid floor.
Related guides
Do rocks in the bottom of a raised bed help drainage?
No. A layer of gravel under soil actually holds water in the soil above it longer. An open bottom over loosened native soil drains better than any rock layer.
Does grass have to be dug out before building a bed?
Not usually. Mow it short and cover it with wet cardboard; the grass dies under the soil within a few months. Dig out aggressive spreading weeds first.
Is landscape fabric a good bed bottom?
Only if the bed sits on gravel, pavers or concrete. On soil, fabric blocks roots and earthworms and doesn't stop determined weeds for long.