Build a raised bed in a weekend with untreated wood, hardware cloth, and soil

A raised bed is a bottomless wooden box filled with soil, sitting directly on the ground. You build it by cutting boards to length, fastening the corners together with screws, placing it where you want it, and filling it with soil and compost. The whole job takes four to six hours for a 4-by-8-foot bed, and you need only a drill, a saw, and a level. No digging out existing grass required—the cardboard underneath kills it as the bed settles.

The most common mistake is using treated lumber, which can leach chemicals into soil over years. Untreated cedar, redwood, or composite boards last longer and are safer. The second mistake is building the bed too deep for what you are growing: leafy greens need 6 inches, root vegetables need 10 to 12 inches, and tomatoes need 18 inches minimum.

Key Takeaways

  • Untreated cedar or composite boards are safer and longer-lasting than pressure-treated lumber for vegetable beds.
  • A 4-by-8-foot bed with 12-inch-deep sides holds enough soil for most vegetables and fits standard garden layouts.
  • Lay cardboard under the bed to block grass and weeds; you do not need to remove sod first.
  • Screw the corners together rather than nailing so you can adjust them square before the soil weight locks them in place.
  • Fill the bed with a mix of topsoil and compost rather than garden soil alone, which compacts over time.

Choose your boards and cut them to length

Buy untreated cedar, redwood, or composite boards at any home center. Cedar and redwood naturally resist rot and last 10 to 15 years in soil contact. Composite boards (wood fiber mixed with plastic) last 15 to 20 years but cost more. Avoid pressure-treated lumber marked with "CCA" or "ACQ"—these contain copper compounds that accumulate in soil.

For a standard 4-by-8-foot bed, you need two 8-foot boards and two 4-foot boards. If you want a deeper bed for tomatoes or root crops, buy 2-by-12 boards instead of 2-by-10. A 2-by-10 board is actually 9.5 inches deep; a 2-by-12 is 11.5 inches deep. Ask the home center to cut the boards to length if you do not have a saw at home—most will do this for free or a small fee.

Assemble the frame with corner screws

Lay the four boards on a flat surface in a rectangle. At each corner, drill two holes through the end of one board into the end grain of the adjacent board, about 2 inches from the top and 2 inches from the bottom. Use a 3/16-inch drill bit so the screw shaft (not the head) passes through cleanly. This prevents the wood from splitting.

Drive a 3-inch exterior-grade wood screw into each hole. Exterior-grade screws resist rust better than standard screws. Tighten them firmly but do not over-torque—you want the boards flush and square, not crushed. Check each corner with a speed square or by measuring diagonally corner to corner; both diagonals should be equal length. If they are not, loosen the screws slightly, tap the frame into square, and retighten.

Position the bed and level it

Choose a spot that gets at least six hours of direct sun for vegetables. Lay cardboard over the grass or weeds where the bed will sit. Overlap the cardboard pieces by at least 6 inches so grass cannot push through the seams. You do not need to remove the sod—cardboard will smother it as the bed settles over the first season.

Set the frame on top of the cardboard and check it with a level in two directions (lengthwise and widthwise). If the ground slopes, you can shim under one side with wood shims or gravel, or you can accept a slight slope—up to 1 inch over 8 feet is fine for most vegetables. Place a level on the soil surface once you have filled the bed; that is what matters for water drainage.

Line the bottom to keep out burrowing pests

If you live in an area with gophers, voles, or moles, lay hardware cloth (a metal mesh, usually 1/2-inch openings) across the bottom of the frame before filling. Staple it to the inside of the boards with a staple gun, or straightforward lay it flat and let the soil weight hold it down. Hardware cloth prevents burrowing animals from tunneling up into your bed from below.

If you do not have burrowing pests, skip this step. The cardboard underneath is enough to block most weeds. If slugs or snails are a problem in your area, hardware cloth will not stop them—they move along the soil surface and climb the sides of the bed. Copper tape around the rim of the frame is more effective for slugs.

Fill the bed with soil and compost

A 4-by-8-foot bed that is 12 inches deep holds about 32 cubic feet of soil. Buy a mix of topsoil and compost rather than garden soil alone. Garden soil compacts heavily over time and drains poorly when confined in a raised bed. A good ratio is two parts topsoil to one part compost, or use a bagged "raised bed mix" if your garden center carries it.

Dump the soil into the bed and rake it level. Water it thoroughly—the soil will settle by 1 to 2 inches over the first week. Top it off with more soil or compost once it settles. Do not plant when ready if you used fresh compost; wait a week so the decomposition heat dissipates. If you used aged compost or bagged mix, you can plant the same day.

Maintain the bed frame over time

Check the corners and edges each spring for rot or loosening. If a board begins to rot at the base, you can replace just that board by unbolting the corners, sliding it out, and sliding a new one in. Cedar and redwood rot slowly, usually starting at the bottom edge where it touches wet soil. Composite boards do not rot but can crack if you over-tighten the corner screws.

As the soil settles and decomposes over the seasons, add 1 to 2 inches of compost each spring. This keeps the bed at full depth and replenishes nutrients. After five to ten years, depending on the wood type, the boards may need replacement. By then, you will know whether raised beds work for your garden and whether to rebuild.

Frequently Asked Questions

Can I use pressure-treated lumber for a vegetable bed?

Pressure-treated lumber marked "CCA" or "ACQ" contains copper compounds that leach into soil and accumulate in vegetables over time. Untreated cedar, redwood, or composite boards are safer. If you already have a treated bed, line it with landscape fabric to reduce contact between soil and wood.

How deep does a raised bed need to be?

Leafy greens and herbs need 6 to 8 inches. Root vegetables like carrots and beets need 10 to 12 inches. Tomatoes, peppers, and other fruiting crops need 18 inches minimum. A 12-inch-deep bed works for most vegetables and is a good middle ground if you grow a mix.

Do I have to remove the grass before building the bed?

No. Lay cardboard over the grass, overlapping the pieces by 6 inches, and set the frame on top. The cardboard smothers the grass over the first season. By the time you plant the next year, the sod underneath has mostly decomposed and become part of the soil.

What is the best size for a raised bed?

A 4-by-8-foot bed is standard because it fits most garden spaces and holds enough soil for a productive garden. A 4-by-4-foot bed is easier to reach into from all sides if you have limited mobility. Avoid beds wider than 4 feet—you will struggle to reach the center without stepping on the soil.

Can I build a raised bed on concrete or pavement?

Yes, but drainage becomes critical. Drill or drill-and-chisel drainage holes in the concrete so water does not pool underneath. Without drainage, roots will rot. Alternatively, place the bed on landscape fabric over the concrete so water can seep through the fabric to the ground below.