What You Need to Build a Raised Bed

A raised garden bed is a wooden or composite box you fill with soil and plant in. To build one, you need four sides (usually boards), corner fasteners (screws or brackets), a level surface, and soil to fill it. Most people use untreated cedar, composite lumber, or galvanized metal. The whole project takes two to four hours for a standard 4-by-8-foot bed, depending on your tools and experience.

The materials cost between $80 and $300 for a single bed, depending on size and what you choose. Cedar costs more upfront but lasts 10 to 15 years. Composite materials last longer but cost 30 to 50 percent more. Galvanized steel is durable and affordable but narrows your planting options because it conducts heat.

You do not need power tools, though a drill makes the work faster. A level, tape measure, saw, and screwdriver are the minimum. If you are buying lumber, ask the supplier to cut it to length — most will do this for free or a small fee, which saves you the cost of a saw if you do not own one.

Key Takeaways

  • Untreated cedar and composite lumber are the most common choices; cedar is cheaper but lasts 10 to 15 years, while composite lasts 20 years or longer.
  • A standard 4-by-8-foot bed requires four boards, corner brackets or screws, a level, and soil; the whole assembly takes two to four hours.
  • Screw the corners together rather than nailing them, because screws hold better as the wood shifts and settles over time.
  • Level the ground before you build, because an unlevel bed will drain unevenly and make watering harder.
  • Fill the bed with a mix of topsoil and compost rather than garden soil alone, because it drains better and holds nutrients longer.

Choosing Your Lumber and Size

Untreated cedar is the standard choice for most home gardeners. It resists rot naturally, costs less than composite, and looks finished without staining. A 4-by-8-foot bed made from 2-by-10 cedar boards costs roughly $120 to $150 in materials. Cedar lasts 10 to 15 years before the wood begins to break down, especially at the corners where water collects.

Composite lumber (wood fiber mixed with plastic) costs 40 to 60 percent more than cedar but lasts 20 to 25 years. It does not rot, splinter, or need staining. Trex and Fiberon are common brands. The trade-off is weight — composite is heavier to move and harder to cut if you need a custom size.

Galvanized steel and aluminum last indefinitely but conduct heat into the soil, which can stress plants in hot climates. Steel is cheaper than composite but more expensive than cedar. Aluminum is lightweight but dents easily.

Avoid pressure-treated lumber unless it is labeled "copper-free". Older pressure-treated wood contains arsenic, which leaches into soil over time. Avoid railroad ties and creosote-treated wood for the same reason.

Standard sizes are 4-by-8 feet, 4-by-4 feet, and 2-by-4 feet. Larger beds are harder to reach into from the sides, so 4 feet wide is a practical limit. Length does not matter as much. A 4-by-8 bed holds about 32 cubic feet of soil and costs less per square foot than a smaller bed because you use fewer corners.

Preparing the Ground and Laying Out the Frame

Choose a spot that gets at least six hours of direct sun and is reasonably level. Remove grass, weeds, and large rocks from the area. You do not need to dig deep — just clear the surface so the boards sit flat.

Use a level to check the ground. If one corner is more than 2 inches lower than another, either dig out the high spots or add soil to the low spots. An unlevel bed drains unevenly: water pools on the low side and the high side dries out faster. This makes watering harder and can kill plants on the dry side.

Lay out your boards in a rectangle on the ground. Use a tape measure to check that opposite sides are equal length and that the diagonals are equal (this confirms the corners are square). Adjust until the frame is square, then mark the corner positions with chalk or a stick so you can find them again when you flip the frame over to fasten it.

Fastening the Corners

Screw the corners together rather than nailing them. Nails work at first, but as the wood dries and shifts, nails loosen and the corners separate. Screws hold better because they grip the wood fibers and tighten as the wood shrinks.

Use 3-inch exterior-grade deck screws, which are long enough to go through one board and into the end grain of the adjacent board. Drill a pilot hole first (a small hole that guides the screw and prevents splitting). Drill at a slight angle — about 15 degrees — so the screw pulls the corners tight.

Use at least two screws per corner, one near the top and one near the bottom. If your boards are 10 inches tall or taller, use three screws. Tighten each screw until it is snug but do not over-tighten, which can strip the wood or bend the screw.

An alternative is a corner bracket — an L-shaped metal piece that bolts to the inside of both boards. Brackets are faster if you are building multiple beds and work well with composite lumber, which is harder to screw into. Brackets cost $5 to $15 per corner.

Setting the Bed in Place and Checking Level

Flip the assembled frame right-side up and position it on the prepared ground. Slide it into place so the corners align with your chalk marks. Use a level on all four sides to check that the frame is level. If one corner is high, either dig out soil under that corner or add soil under the low corners.

Do not rely on the frame itself to level the ground — the frame will flex and settle unevenly if the ground underneath is not level. Spend time on this step. A level bed is easier to water and drains evenly.

If the ground is very uneven, you can dig a shallow trench around the perimeter and set the frame into it. This takes longer but ensures the frame sits stable and level.

Filling and Settling

Fill the bed with a mix of topsoil and compost. A common ratio is 60 percent topsoil and 40 percent compost, though you can adjust based on what you are growing. Compost holds moisture and nutrients; topsoil provides structure and drainage. Garden soil alone is too dense and drains poorly.

A 4-by-8-foot bed that is 10 inches deep holds about 26 cubic yards of soil. Most suppliers sell soil by the cubic yard. Order slightly more than you think you need, because soil settles as it dries and compacts.

Fill the bed in layers if you are mixing topsoil and compost. Spread half the topsoil, then half the compost, then the rest of the topsoil, then the rest of the compost. This distributes nutrients evenly. Water lightly as you fill so the soil settles and compacts.

The soil will settle over the first few weeks. You may need to add more soil after a month to bring it back to the top of the frame. This is normal and expected.

Protecting the Wood and Long-Term Care

Cedar does not need sealing or staining to function, but staining extends its life. If you stain, use a water-based exterior stain, not paint, which traps moisture and speeds rot. Stain every two to three years. Do not use varnish or polyurethane, which peel and create maintenance work.

Composite lumber does not need staining. Wipe it down with a damp cloth if it gets dirty, but that is the only maintenance.

Check the corners every spring. If screws have loosened, tighten them. If wood is soft or crumbling at the corners, that board is rotting and needs replacement. Cedar corners usually last 8 to 10 years before they need replacing; you can replace a single board without rebuilding the whole bed.

Do not let water sit against the wood. If you have a drip line or soaker hose, position it so water does not pool against the frame. This slows rot and extends the life of the bed.

Frequently Asked Questions

Can I build a raised bed on concrete or a patio?

Yes, but drainage is the issue. Concrete blocks water from draining down, so the soil stays wet and roots rot. Drill drainage holes in the bottom of the frame or set it on gravel so water can escape underneath. Alternatively, line the bottom with landscape fabric and drill holes through it.

How deep should a raised bed be?

Eight to 12 inches is standard for most vegetables. Root vegetables like carrots and beets need 12 inches or more. Shallow-rooted plants like lettuce and herbs do fine in 6 to 8 inches. Deeper beds hold more water and require less frequent watering, but cost more to fill.

Do I need a bottom or liner?

No, unless you are building on concrete or contaminated soil. A bottom blocks drainage and traps water. If you want to keep burrowing pests out, line the bottom with hardware cloth (a metal mesh), but leave gaps so water drains.

What is the best wood for a raised bed in a hot climate?

Cedar or composite lumber. Avoid galvanized steel and aluminum, which conduct heat and can cook roots on hot days. If you use metal, paint it white or cover it with shade cloth in summer.

Can I use reclaimed wood from a barn or old building?

Only if you know what it was treated with. Reclaimed wood from barns, sheds, or old houses may contain lead paint, creosote, or other toxins. If you cannot confirm the wood is safe, buy new cedar or composite instead.