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 and costs between $50 and $200 depending on materials and size. You need four boards (usually 2-by-10 or 2-by-12 lumber), corner brackets or screws, a drill or screwdriver, a saw if you're cutting boards to length, and a level. Most people build beds 4 feet long by 2 feet wide by 10 to 12 inches deep, though you can adjust these dimensions to fit your space.

The most common mistake is buying untreated wood that will rot in three to five years. Cedar and redwood naturally resist rot and last 10 to 15 years. Pressure-treated lumber rated for ground contact (marked "UC3B" or "UC4") also works and costs less, though some gardeners avoid it due to chemical concerns—research your local regulations. Composite boards made from wood fiber and plastic last longer but cost two to three times more. Avoid railroad ties and old utility poles; they contain creosote, which leaches into soil.

Key Takeaways

  • Cedar or pressure-treated lumber rated for ground contact will last 10 or more years, while untreated wood rots within three to five years.
  • A standard 4-by-2-foot bed requires four boards, corner brackets or deck screws, a drill, and a level—most hardware stores will cut boards to length for free.
  • Assemble the frame on level ground, check all corners with a level, and add landscape fabric to the bottom to block weeds without preventing drainage.
  • Fill your bed with a mix of topsoil, compost, and peat moss or coconut coir rather than garden soil alone, which compacts over time.

Choosing Your Location and Preparing the Ground

Pick a spot that gets at least six hours of direct sun for vegetables, or three to four hours for leafy greens. Avoid low spots where water pools after rain—raised beds drain better than ground beds, but standing water still causes root rot. Clear away grass, weeds, and debris from the area where your bed will sit. You do not need to remove the top layer of soil, but do pull out any large rocks or roots.

Use a level to check that your ground is reasonably flat. A bed that slopes more than a few inches will cause water to pool on one side and dry out on the other. If your ground is very uneven, you can dig out the high spots and fill the low spots, or build the bed slightly larger and adjust the board heights at each corner. Do not worry about making it perfectly level—close is good enough.

Cutting and Assembling the Frame

Measure your space and decide on bed dimensions. A 4-by-2-foot bed is straightforward to reach across and fits most spaces. If you want a different size, aim for a width of 2 to 3 feet so you can reach the center from either side without stepping into the bed. Most hardware stores will cut boards to length for free when you buy them, so ask them to cut two boards to your length and two to your width.

Lay the four boards on flat ground in a rectangle. Drill pilot holes (small starter holes) at each corner to prevent the wood from splitting. Use either corner brackets (metal L-shaped pieces bolted to the inside corners) or deck screws (3-inch exterior-grade screws driven through one board into the end of the next). Brackets are faster and more durable; screws are cheaper. Drive two fasteners per corner. Check each corner with a level as you tighten—the frame should sit flat, not tilted.

Placing the Frame and Adding Landscape Fabric

Move the assembled frame to your prepared ground and set it in place. Use a level to check that the top edges are even all the way around. If one corner sits higher than the others, you can shim it by sliding a shingle or thin wood piece underneath, or you can dig out soil from the high side. This step matters because water will run toward the low corner and leave the high side dry.

Once the frame is level, line the bottom with landscape fabric (a woven cloth that blocks weeds but lets water through). Overlap the seams by 6 inches and staple the fabric to the inside of the boards. This step prevents grass and perennial weeds from growing up into your bed. Do not use plastic sheeting—it traps water and causes root rot. If you skip the fabric, you will spend the season pulling weeds from the bottom of your bed.

Filling Your Bed With Soil

Do not fill a raised bed with garden soil alone. Garden soil compacts over time and drains poorly in a raised bed. Instead, mix three parts topsoil, two parts compost, and one part peat moss or coconut coir. This blend drains well, holds nutrients, and stays loose enough for roots to grow. You can buy these materials by the bag or cubic yard. A 4-by-2-foot bed that is 10 inches deep needs about 6 cubic feet of soil, or roughly 8 to 10 bags of bagged soil.

Dump the soil into the bed and mix it with a shovel or garden fork. Water it lightly as you fill—this helps the soil settle and makes it easier to work. Let the bed sit for a day or two before planting so the soil can compress slightly. The soil level will drop an inch or two as it settles, which is normal. You can add more soil later if needed, but most gardeners find they need to top off their beds once a year as the organic matter breaks down.

Protecting Your Bed From Pests and Weather

Once your bed is filled and settled, you can plant right away. If you live in an area with burrowing animals like gophers or moles, add a layer of hardware cloth (a metal mesh) to the bottom before you add soil. Staple it to the inside of the frame so animals cannot push through from below. This adds cost and labor but prevents years of frustration.

In very hot climates, consider adding a shade cloth frame during summer to protect leafy greens from bolting. In cold climates, you can cover the bed with row covers or cold frames in spring and fall to extend your growing season. These are optional upgrades—a basic raised bed works fine without them, but they solve specific problems if you run into them.

Maintaining Your Raised Bed Year to Year

At the end of each growing season, add 2 to 3 inches of compost to the top of your bed. This replaces the organic matter that broke down during the year and keeps the soil rich. Do not remove the old soil—just layer new material on top. Over time, the bed will settle and compress, so you may need to add soil every year or two to keep it at the original depth.

Check the frame for rot or damage each spring. Cedar and pressure-treated wood last a long time, but boards can split or warp. If a board cracks but is still structurally sound, you can leave it. If it is rotting or falling apart, replace it by unbolting the corner brackets and sliding out the damaged board. Keep the landscape fabric in place and add a new board in its place.

Frequently Asked Questions

Can I build a raised bed directly on top of grass?

Yes. The landscape fabric will block the grass underneath, and it will eventually decompose. You do not need to remove the sod first, though pulling it back saves you from having to dig it out later if the fabric tears. If you leave the grass in place, it will take a season or two to fully break down.

How deep does a raised bed need to be?

Ten to twelve inches works for most vegetables and herbs. Root vegetables like carrots and beets need 12 inches minimum. Shallow-rooted plants like lettuce and spinach can grow in 6 to 8 inches. Deeper is always better if you have the space and budget—it gives roots more room and holds more moisture.

What kind of wood should I avoid?

Avoid untreated pine, which rots in three to five years. Do not use railroad ties, creosoted utility poles, or wood treated with chromated copper arsenate (CCA), an older preservative. Cedar, redwood, and pressure-treated lumber rated UC3B or UC4 are safe choices that last 10 or more years.

Do I need to add a bottom to my raised bed?

No. A solid bottom traps water and causes root rot. Landscape fabric alone is enough to block weeds while letting water drain. Add hardware cloth only if you have burrowing animals in your area.

How much does it cost to build a raised bed?

A basic 4-by-2-foot bed with cedar boards costs $80 to $120. Pressure-treated lumber costs $50 to $80. Composite boards cost $150 to $250. Soil and compost to fill it add another $40 to $80 depending on whether you buy bagged or bulk material.