What You Need to Build a Basic Raised Bed

A raised bed box is a four-sided frame you fill with soil and plant into. The simplest version uses untreated wood boards, corner posts, and fasteners—no special tools or carpentry experience required. Most people build one in an afternoon using materials from a hardware store and a drill or screwdriver.

The standard size is 4 feet long, 2 feet wide, and 12 inches deep, though you can adjust these to fit your space. Depth matters most: 12 inches works for most vegetables and herbs; root crops like carrots need at least 12 inches, while leafy greens can grow in 8 inches. Length and width depend on what fits in your yard and how far you can comfortably reach into the center without stepping inside.

Key Takeaways

  • Untreated cedar or composite boards last longer than pine, but pine is cheaper and works fine if replaced every five to seven years.
  • You need four boards, four corner posts, sixteen fasteners (screws or bolts), a drill or screwdriver, and a level to check that the frame sits flat.
  • Screw the boards to the posts from the outside so the frame sits flush and you can fill it completely with soil.
  • Lay landscape fabric on the bottom to block weeds, then fill with soil and water it down before planting.

Choosing Wood and Materials

Untreated cedar resists rot naturally and lasts 10 to 15 years. It costs more than pine but saves you from replacing the bed sooner. Composite boards (wood fiber mixed with plastic) last 20+ years and never rot, but cost significantly more upfront and are heavier to handle.

Pressure-treated wood was once common but is now avoided for vegetable beds because the chemicals can leach into soil. Avoid it. Pine boards are the cheapest option and work fine—they typically last five to seven years before the bottom boards rot out. Many gardeners replace them on that schedule and accept it as a maintenance cost.

For a 4-by-2-foot bed, you need two 4-foot boards and two 2-foot boards, all the same thickness (usually 2 inches nominal, which is actually 1.5 inches). You also need four corner posts—2-by-2 lumber, 12 to 18 inches long. Posts longer than 12 inches let you drive them into the ground for extra stability, which is useful on sloped yards.

Fastening the Frame Together

Lay the four boards in a rectangle on flat ground. Stand a corner post at each corner, on the outside of the frame. The post should be flush with the top of the boards and centered on the corner so equal wood shows on both sides.

Drill pilot holes through each board into the post—this prevents the wood from splitting. Use 3-inch exterior screws (two per corner, one near the top and one near the bottom) or 3/8-inch bolts with washers and nuts. Screws are faster; bolts are stronger and last longer. Drive or tighten all fasteners snugly but not so hard you crush the wood.

Once all four corners are fastened, flip the frame over and check it with a level. If one corner sits higher than the others, you can shim it by placing a shim (a thin wedge of wood or plastic) under the low corner, or dig out soil under the high corner. The frame does not have to be perfectly level, but a slope of more than a few inches will cause water to pool on one side.

Preparing the Ground and Positioning the Bed

Choose a spot that gets at least six hours of direct sun for vegetables, or three to four hours for leafy greens and herbs. Clear away grass, weeds, and debris from the area where the bed will sit. You do not have to remove the sod completely—the landscape fabric will block it—but removing it makes the bed sit flatter and gives you more usable soil depth.

Set the frame in place and check it with a level again. If the ground is very uneven, you can dig out the high spots or add soil under the low spots. Once you are satisfied, lay landscape fabric (also called weed cloth) across the bottom, overlapping the edges by a few inches. Staple it to the inside of the boards or just weigh it down with soil—it will stay in place once the bed is full.

Filling and Watering the Bed

Fill the frame with soil mix. Most gardeners use a blend of topsoil, compost, and peat moss or coconut coir in roughly equal parts, though any combination of topsoil and compost works. Avoid filling with pure compost—it settles and compacts over time. Avoid pure topsoil—it drains poorly and compacts easily under foot traffic.

Fill the bed to within an inch of the top. Water it thoroughly and let it sit for a day or two. The soil will settle, and you may need to add more. This settling is normal and happens every year as organic matter breaks down. You will typically add 1 to 2 inches of compost each spring to top it back up.

Common Mistakes to Avoid

The most common error is fastening the boards to the inside of the posts instead of the outside. This leaves a gap between the board and the post, and soil spills out through the gap. Always fasten from the outside so the boards sit flush against the posts.

Another mistake is skipping the landscape fabric. Without it, grass and weeds grow up through the bottom of the bed and compete with your plants. Fabric blocks them while still letting water drain. Do not use plastic sheeting—it traps water and rots the bottom boards.

Filling the bed with only compost or only topsoil is also common. Compost alone settles too much; topsoil alone drains poorly and compacts. A mix gives you both drainage and nutrients. If you are on a tight budget, use whatever you have and plan to add compost each year.

When to Call a Professional

Building a raised bed is a straightforward project for most people. You do not need a professional unless your yard is on a steep slope, the ground is extremely hard or rocky, or you want a very large or complex design.

If you are unsure about your soil or want to test it before planting, a local extension office can run a soil test for a small fee—that is worth doing before you invest in a full bed. Extension offices are run by your state's land-grant university and offer free or low-cost soil testing and gardening information specific to your region.

Frequently Asked Questions

Can I build a raised bed without corner posts?

Yes, but it is less stable. You can overlap the boards at the corners (like a log cabin) and fasten them together, or use metal corner brackets on the inside. Posts are simpler and stronger, especially for larger beds or if you plan to fill the bed with heavy, wet soil.

How deep does a raised bed need to be?

Twelve inches is the standard and works for most vegetables, herbs, and flowers. Shallow-rooted plants like lettuce and spinach can grow in 8 inches. Root crops like carrots, beets, and parsnips need at least 12 inches, and some prefer 18. Deeper is always better if you have the space and budget.

What is the best wood for a raised bed?

Cedar lasts longest and resists rot naturally. Pine is cheaper and works fine for five to seven years. Composite boards last 20+ years but cost more. Avoid pressure-treated wood for vegetable beds. Choose based on your budget and how often you want to replace the bed.

Do I need to line the bottom of the bed?

Landscape fabric blocks weeds and grass from growing up through the bottom. It is not required, but it saves you years of weeding. Do not use plastic—it traps water and rots the bottom boards. Fabric lets water drain while blocking weeds.

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

Yes, but you will need to water more often because water cannot drain into the ground below. Use landscape fabric to prevent the concrete from wicking moisture away from the soil. The bed will work, but it will dry out faster than one on bare ground.