What You Need to Build a Raised Bed

A raised bed is a wooden or composite box you fill with soil and plant into. Building one takes a weekend afternoon and requires only basic tools—a drill, a saw, and a level. The simplest design is a rectangular frame made from untreated wood boards, held together at the corners with screws or brackets.

You will need four boards (typically 2-by-10 or 2-by-12 lumber), four corner brackets or L-brackets, a drill with a screwdriver bit, wood screws (3-inch exterior-grade), a circular saw or hand saw, a level, and a measuring tape. If you are building on grass or soil, you may also want landscape fabric to line the bottom and prevent weeds from growing up through the bed.

Most raised beds are 4 feet long by 2 feet wide by 10 to 12 inches deep, though you can adjust these dimensions to fit your space. A bed this size holds roughly 8 cubic feet of soil and is wide enough to reach the center from either side without stepping inside.

Key Takeaways

  • Cut four boards to length, drill pilot holes at each corner, and fasten them together with 3-inch exterior-grade screws or metal L-brackets.
  • Set the frame on level ground, check that all corners are square using the 3-4-5 method, and adjust until the frame sits flat.
  • Line the bottom with landscape fabric if you are building on grass or soil to block weeds from growing upward into your bed.
  • Fill the bed with a mix of topsoil and compost, water it thoroughly, and let it settle for a few days before planting.

Cutting and Preparing Your Boards

Start by deciding on your bed dimensions. A 4-by-2-foot frame is standard and manageable for most gardeners. If you are using 2-by-10 boards, you will need two boards cut to 4 feet (the long sides) and two cut to 2 feet (the short sides). If your boards come longer than you need, use a circular saw or hand saw to cut them to length. Wear safety glasses and measure twice before cutting.

After cutting, inspect the boards for large splinters or damage. Sand down any rough edges where you will be handling the wood. If you are using untreated wood, it will last 5 to 10 years depending on your climate; treated wood lasts longer but costs more. Do not use pressure-treated wood from before 2004, as it contains arsenic.

Assembling the Frame at the Corners

Lay your four boards on a flat surface in a rectangle. At each corner, you have two options: drill pilot holes and use 3-inch exterior-grade wood screws, or use metal L-brackets bolted or screwed to the inside of the frame.

If you are using screws, drill a pilot hole (a small hole that guides the screw) about 1 inch from the end of each board, angled slightly inward so the screw pulls the corners tight. Drive two screws per corner, one near the top and one near the bottom. This prevents the frame from racking (twisting out of square) as it weathers.

If you are using L-brackets, position the bracket on the inside corner and drill holes through the bracket into both boards. Use bolts or lag screws to fasten it. Brackets are stronger and easier to disassemble later if you need to move the bed.

Leveling and Positioning Your Bed

Move your assembled frame to the location where it will sit. Choose a spot that gets at least 6 hours of direct sun per day and is relatively level. Place the frame on the ground and use a level to check if it sits flat. If one corner is higher than the others, you can dig out soil under the high corner or add soil under the low corners until the frame is level.

Check that all four corners are square using the 3-4-5 method: measure 3 feet along one side from a corner, 4 feet along the adjacent side from the same corner, and measure the diagonal distance between those two points. If the diagonal measures 5 feet, the corner is square. Adjust the frame until all four corners pass this test.

Once the frame is level and square, you can anchor it to the ground if you live in a windy area. Drive 12-inch stakes or rebar through the frame into the soil at each corner, or screw the frame directly to the ground if you are building on a patio or deck.

Lining the Bottom and Adding Soil

If you are building on grass or bare soil, lay landscape fabric across the bottom of the frame before filling it. This blocks weeds and grass from growing up into your bed while still allowing water to drain. Overlap the edges by 6 inches and staple or pin the fabric to the inside of the frame. You do not need fabric if you are building on concrete or pavement.

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. For a 4-by-2-foot bed that is 10 inches deep, you will need roughly 5 to 6 cubic yards of soil. Water the bed thoroughly after filling it; the soil will settle over a few days, and you may need to add more to bring it back to the top.

Let the bed sit for at least three days before planting. This allows the soil to settle and the compost to begin breaking down. If you are planting when ready, water deeply and watch for settling over the first week.

Common Mistakes to Avoid

The most common error is building the frame on uneven ground and not checking for level. An unlevel bed causes water to pool in one corner and dry out in another, creating inconsistent growing conditions. Always use a level and adjust the ground before filling.

Another mistake is using treated wood that is too old or of unknown origin. Pressure-treated lumber from before 2004 can leach harmful chemicals into the soil. Stick with untreated wood, composite boards, or wood treated after 2004 with copper-based preservatives.

Skipping the landscape fabric is tempting but often regretted. Without it, grass and weeds will grow up through the bottom of the bed and compete with your plants. Fabric is inexpensive and saves months of weeding.

Finally, do not skimp on soil depth. A bed that is only 6 inches deep limits what you can grow. Most vegetables need 8 to 12 inches of soil to develop healthy roots. Shallow beds work for herbs and shallow-rooted greens, but plan for at least 10 inches if you want flexibility.

Frequently Asked Questions

How much does it cost to build a raised bed?

A basic 4-by-2-foot bed made from untreated 2-by-10 boards costs $30 to $50 for lumber and hardware. Soil and compost to fill it cost $40 to $80 depending on your location and whether you buy in bulk. Total cost is typically $70 to $130 for a complete bed ready to plant.

Can I build a raised bed on top of concrete or pavement?

Yes. You do not need landscape fabric if you are building on concrete, since nothing can grow through it. Fill the bed with soil as usual. Concrete beds warm up faster in spring and cool down faster in fall, which can be an advantage or disadvantage depending on what you are growing.

How long does untreated wood last in a raised bed?

Untreated wood typically lasts 5 to 10 years in a raised bed, depending on your climate and how wet the soil stays. Wood in dry climates lasts longer. You can extend the life by staining the outside with a non-toxic wood stain, though avoid sealing the inside where it touches soil.

Do I need to replace the soil every year?

No. Add 1 to 2 inches of compost to the top each spring to replenish nutrients and organic matter. After 3 to 5 years, you may want to replace the bottom 4 to 6 inches of soil if it has compacted heavily, but most of the original soil can stay in place.

What size raised bed should I build?

A 4-by-2-foot bed is the standard size and works well for most gardeners. If you have limited space, a 4-by-1-foot bed is manageable. Avoid beds wider than 3 feet, since you will not be able to reach the center without stepping inside and compacting the soil.