Build a raised bed by stacking untreated wood boards into a rectangle, securing the corners, and filling it with soil

A raised bed is a wooden or composite box you fill with soil and plant directly into. You build it by cutting boards to length, joining them at the corners with screws or brackets, and setting it on level ground. The whole project takes two to four hours and costs between $40 and $150 depending on the wood you choose and the bed's size. Most home gardeners use boards that are 2 inches thick and 8 to 12 inches tall, which gives roots enough depth for most vegetables while keeping the bed straightforward to reach.

The most common mistake is using treated wood that contains copper or arsenic—these chemicals leach into soil over time. Use untreated cedar, redwood, or composite boards instead. Cedar and redwood last five to ten years outdoors. Composite boards (made from wood fiber and plastic) cost more upfront but last fifteen to twenty years and don't rot or splinter.

Key Takeaways

  • Untreated cedar or redwood boards are safer than pressure-treated wood because they don't leach chemicals into the soil where your vegetables grow.
  • A 4-by-8-foot bed with 12-inch-tall boards is a standard size that holds enough soil for most vegetables and stays within comfortable reaching distance.
  • find corners with galvanized deck screws or L-brackets rather than nails, which loosen as the wood shifts and settles.
  • Set the bed on level ground and line the bottom with hardware cloth if gophers or moles are active in your area.
  • Fill the bed with a mix of topsoil, compost, and peat moss or coconut coir rather than garden soil alone, which compacts over time.

Measure and cut your boards to the right length

Decide on your bed's outer dimensions first. A 4-by-8-foot bed is the most popular size—it's large enough to grow a variety of vegetables but narrow enough that you can reach the center from either side without stepping into the bed. If you have limited space, a 2-by-4-foot or 3-by-6-foot bed works well. Write down the length and width you want.

Buy untreated boards that are 2 inches thick (called "2-by-12" if you want 12 inches of height, or "2-by-10" for 10 inches). The "2-by" measurement is the actual thickness; the second number is the height. For a 4-by-8-foot bed, you need two boards 8 feet long and two boards 4 feet long. Have the lumber yard cut them to length if you don't have a saw at home—most yards do this for free or a small fee. Measure twice before cutting; boards are expensive to replace.

Assemble the corners with screws or brackets

Lay the four boards on level ground in a rectangle shape. The two long boards should overlap the two short boards at the corners (the short boards sit on top). This overlap gives you a solid surface to screw into.

Use galvanized deck screws, which resist rust. A 3-inch screw is standard for 2-inch-thick boards. Drill two or three screws through each short board into the end of each long board. If you don't have a drill, use an L-bracket (a metal corner brace) on the inside of each corner instead—these are sold at hardware stores and require only a screwdriver. Brackets are slower but just as strong and don't require a drill.

Check that all four corners are square by measuring diagonally from corner to corner. Both diagonal measurements should be the same length. If they're not, nudge the boards until they match. Tighten all screws or bolts fully before moving the bed.

Position the bed on level ground and add a barrier if needed

Move the assembled bed to its final location. It should sit on flat, level ground. If the ground slopes, dig out the high side and fill in the low side until the bed sits level. A bed that tilts will hold water unevenly and make it hard to water plants fairly.

If gophers, moles, or burrowing rodents are common in your area, line the bottom of the bed with hardware cloth (a metal mesh with half-inch holes). Lay it flat on the ground inside the bed before you add soil. This keeps burrowing animals from tunneling up into your vegetables. If you don't have a rodent problem, skip this step—it's not necessary.

Fill the bed with the right soil mixture

Don't use garden soil alone. Garden soil compacts over time and drains poorly in a raised bed. Instead, mix three ingredients: topsoil, compost, and peat moss or coconut coir. A common ratio is one-third of each. For a 4-by-8-foot bed that's 12 inches deep, you'll need about 32 cubic feet of soil mix, which is roughly 1.2 cubic yards. Most garden centers sell soil by the bag or cubic yard.

Dump the topsoil into the bed first, then add the compost, then the peat moss or coir. Mix it together with a shovel or garden fork until the colors are even. The bed will settle over the first few weeks as the soil compacts, so fill it slightly higher than the rim—about an inch above the top of the boards. Water it thoroughly after filling to help it settle.

Common mistakes to avoid

Using pressure-treated wood is the biggest mistake. The chemicals in treated lumber—especially older lumber treated with arsenic—leach into soil and accumulate in vegetables over years. Untreated cedar costs a bit more but is worth it for safety.

Filling the bed with only garden soil is the second common error. Garden soil is too dense and compacts into a brick-like texture within a season. The three-part mix (topsoil, compost, peat or coir) stays loose and drains well for years.

Building the bed on sloped ground causes water to pool on one side and dry out on the other. Spend time leveling the ground before assembly. If your yard is very sloped, consider building multiple smaller beds on different levels instead of one large bed.

Undersizing the bed is also common. A bed narrower than 3 feet wide forces you to reach too far to the center, and a bed shorter than 10 inches doesn't give roots enough depth for most vegetables. Aim for at least 12 inches of height and no more than 4 feet wide.

Frequently Asked Questions

How deep should a raised bed be?

Most vegetables need 10 to 12 inches of soil depth. Shallow-rooted crops like lettuce and spinach can grow in 8 inches, but tomatoes, peppers, and root vegetables like carrots need at least 12 inches. If you're growing a mix, build 12 inches tall to cover all bases.

Can I use composite boards instead of wood?

Yes. Composite boards (wood fiber mixed with plastic) cost more upfront—usually $2 to $4 per linear foot versus $1 to $2 for cedar—but they last much longer and never rot or splinter. They're a good choice if you want the bed to last fifteen to twenty years without replacement.

What if my yard is too sloped to level?

Build the bed with one side taller than the other to match the slope. Measure the height difference across the width of your bed, then cut the boards on the downhill side shorter and the boards on the uphill side taller. The soil surface will still be level even though the frame isn't.

Do I need to line the bottom with cardboard?

Cardboard is optional. It blocks weeds from growing up into the bed for the first year or two, but it breaks down and stops working after that. Hardware cloth is better if you have burrowing animals. If you have neither problem, skip both and just fill the bed with soil.

How much does it cost to build a raised bed?

A 4-by-8-foot bed with untreated cedar boards costs roughly $60 to $80 for the wood and hardware, plus $40 to $60 for soil and compost to fill it. Composite boards cost more—around $150 to $200 for the frame alone. Budget $100 to $150 total for a cedar bed and $200 to $250 for composite.