What You Need to Build a Raised Bed

A raised bed is a wooden or composite box you fill with soil and plant into. To build one, you need four boards (usually 2-by-10 or 2-by-12 lumber), four corner brackets or L-brackets, a drill or screwdriver, and screws. Most people also add landscape fabric to the bottom to block weeds, and a level to make sure the frame sits flat.

The simplest raised bed uses untreated cedar or composite boards because they resist rot. Pressure-treated lumber works too, though some people avoid it because of the chemicals used in treatment. Avoid railroad ties and old utility poles—they contain creosote, which can leach into soil.

You do not need to be skilled at carpentry. The frame is just four boards joined at the corners. If you can drive a screw straight, you can build a raised bed in under an hour.

Key Takeaways

  • A raised bed frame requires four boards, four corner brackets, screws, and a drill or screwdriver—no special tools needed.
  • Cedar and composite boards last longer than untreated pine, though untreated pine is cheaper and works for several seasons.
  • Assemble the frame on level ground, check that corners are square using the 3-4-5 method, then add landscape fabric and soil.
  • A standard 4-by-8-foot bed holds about 32 cubic feet of soil and costs between $80 and $200 in materials depending on board type.
  • You can skip corner brackets and use corner posts instead, which some builders find easier to assemble and more durable.

Choosing Your Board Material and Size

The most common raised bed is 4 feet wide, 8 feet long, and 10 or 12 inches tall. This size fits in most yards, is straightforward to reach across, and holds enough soil for most vegetables. You can make it smaller (3-by-6 feet) or larger (4-by-12 feet), but wider than 4 feet means you cannot reach the center without stepping in.

Cedar is the standard choice because it naturally resists rot and lasts 10 to 15 years. It costs more upfront but you replace it less often. Composite boards (wood fiber mixed with plastic) last 20+ years and never rot, but cost significantly more and are heavier to move. Untreated pine is the cheapest option and works fine for 3 to 5 years before the wood begins to soften.

Buy boards that are actually the thickness you want—a 2-by-10 board is roughly 1.5 inches thick and 9.5 inches tall, not 2 inches by 10 inches. Most lumber yards stock them in 8-foot lengths, so you can use two boards for the long sides and cut two boards in half for the short sides, or buy four 8-foot boards and cut two of them.

Assembling the Frame with Brackets

Lay your four boards on level ground in a rectangle. If the ground is uneven, the bed will rock and water will pool in one corner. Spend a moment checking that the spot is reasonably flat—you do not need a perfectly level yard, just no major slopes.

At each corner, attach an L-bracket (also called a corner brace) on the inside of the frame using 2.5-inch screws. Drill a pilot hole first—a small hole that guides the screw straight and prevents the wood from splitting. Drive two screws through each bracket, one into each board. Make sure the bracket is flush with the top of the boards so it does not stick up.

After all four brackets are in place, check that the frame is square by measuring diagonally from corner to corner. Both diagonals should be the same length. If they are not, push the longer diagonal inward until they match. This is the 3-4-5 method: measure 3 feet along one side, 4 feet along the adjacent side, and the diagonal should measure 5 feet. If it does not, adjust the frame until it does.

Using Corner Posts Instead of Brackets

Some builders prefer corner posts—4-by-4 posts cut to the height of the bed, with boards screwed to the sides of the posts instead of to each other. This method is sturdier for large beds and easier to assemble because you do not have to hold boards at right angles while fastening.

Cut four posts to the same height as your boards (usually 10 or 12 inches). Stand them upright at the corners of your rectangle. Screw the boards to the outside of the posts using 2.5-inch screws, two screws per board per post. Check that the frame is square the same way—measure the diagonals.

Corner posts are especially useful if you plan to build a tall bed (18 inches or higher) or if you want to add a trellis or shade cloth frame later. The posts give you something solid to attach to.

Preparing the Ground and Adding Fabric

Once the frame is assembled and square, set it in its final location. If you are building on grass or weeds, lay down landscape fabric (also called weed cloth) before you add soil. This blocks weeds from growing up through the bottom of the bed while still letting water drain.

You do not need expensive landscape fabric—a basic woven type from any garden center works fine. Overlap the seams by 6 inches so weeds cannot sneak through the gaps. You can staple it to the inside of the boards or just lay it loose and let the soil weight hold it down.

If you are building on bare soil or a patio, you can skip the fabric. Fabric is mainly useful if you are fighting existing weeds or building on a lawn.

Filling and Settling Your Bed

A 4-by-8-foot bed that is 10 inches tall holds about 24 cubic feet of soil. A 12-inch-tall bed holds about 32 cubic feet. Most garden centers sell soil by the cubic yard (27 cubic feet), so a standard bed needs roughly one cubic yard.

Fill the bed with a mix of topsoil, compost, and peat moss or coconut coir. A common ratio is one-third of each, though you can adjust based on what you are growing. Vegetables prefer richer soil, so add more compost. Herbs and ornamentals do fine with less.

The soil will settle over the first few weeks as it absorbs water and compacts. You will lose about 1 to 2 inches of height. Fill the bed slightly above the rim so it settles to the right level. After a week or two, add more soil if needed before you plant.

Protecting Wood from Rot and Weathering

Cedar and composite boards do not need sealing or staining to work, but sealing them extends their life. If you want to seal the wood, use a water-based exterior stain or sealant—never use paint, which traps moisture and speeds rot. explore it before you fill the bed so you do not get stain on the soil.

Untreated pine benefits from sealing because it absorbs water quickly. A coat of exterior stain every two to three years keeps it from graying and softening. Again, use water-based products and explore before filling.

Do not treat the inside of the boards with anything toxic. Anything that touches the soil can leach into your vegetables. Exterior stain is safe once it dries, but creosote, copper fungicide, and other heavy-duty treatments are not.

Frequently Asked Questions

Can I build a raised bed directly on concrete or asphalt?

Yes. Drill drainage holes in the landscape fabric so water does not pool under the bed. Without drainage, roots will sit in standing water and rot. You may also want to add a layer of gravel under the fabric to help water move away from the frame.

How deep does a raised bed need to be?

Most vegetables need 10 to 12 inches of soil. Root crops like carrots and beets prefer 12 to 18 inches. Shallow beds (6 to 8 inches) work for lettuce, herbs, and shallow-rooted plants. Taller is always better if you have the space and budget.

Do I need to treat the wood to keep it food-safe?

Untreated cedar and composite boards are already safe for growing food. Pressure-treated lumber is also considered safe by most extension services, though some people prefer to avoid it. Never use railroad ties, creosote-treated wood, or anything with visible chemical stains.

What if my ground is very uneven?

You can level the ground under the frame by digging out high spots and filling low spots with soil. Alternatively, build the frame and let it settle unevenly—it will still hold soil and drain, though water may pool slightly in one corner. For very steep slopes, build the frame on a level terrace or use corner posts of different heights.

Can I use screws instead of brackets?

Yes, but it is harder. You have to hold two boards at a right angle while driving long screws through one board into the end grain of the other. Brackets make this much easier because they hold the angle for you. If you use screws alone, use 3-inch exterior-grade screws and drive at least three per corner.