What You Need to Build a Raised Bed

A raised garden bed made from wood is a frame you build yourself from lumber, soil, and fasteners. You choose the size and depth, set it on level ground, fill it with soil, and plant directly into it. Most people build them in a weekend with basic tools—a saw, a drill, and a level—and the whole project costs between $50 and $200 depending on the wood type and bed size.

The most common design is a rectangular box made from four boards joined at the corners. You can build it on grass, bare soil, or a patio. The wood sits directly on the ground; you do not need a foundation. Once it is assembled and level, you add landscape fabric to the bottom to block weeds, then fill it with garden soil and compost.

Key Takeaways

  • Cedar and composite lumber last longest (10+ years), while untreated pine lasts 3 to 5 years and requires replacement sooner.
  • A 4-by-8-foot bed 12 inches deep is a standard size that holds about 32 cubic feet of soil and is straightforward to reach across.
  • Assemble the frame on the ground with corner brackets or screws, check it with a level, then add landscape fabric and soil.
  • Avoid pressure-treated wood from before 2004 because it contains arsenic; newer pressure-treated lumber is safe for vegetable gardens.

Choosing the Right Wood

Cedar is the most popular choice because it resists rot naturally and lasts 10 to 15 years. It costs more upfront—roughly $2 to $4 per linear foot—but you will not need to replace it for a decade. Cedar also smells pleasant and looks finished without staining.

Composite lumber (wood fibers mixed with plastic) lasts 20+ years and never rots, but costs $4 to $6 per linear foot and can feel plastic-like. It is a good choice if you want to build once and forget about it.

Untreated pine is the cheapest option at $1 to $2 per linear foot, but it rots in 3 to 5 years and will need replacing. Many gardeners use it anyway because the low cost makes replacement painless.

Pressure-treated lumber made after 2004 is safe for vegetable gardens—the arsenic was removed from the treatment formula. Older pressure-treated wood (pre-2004) should not touch soil where you grow food. Pressure-treated lumber costs $1.50 to $3 per linear foot and lasts 10 to 15 years.

Avoid railroad ties and old utility poles; they are treated with creosote, which leaches into soil. Do not use plywood or particle board—they break down too quickly when wet.

Sizing and Depth Decisions

The depth you choose depends on what you want to grow. Shallow-rooted crops like lettuce, spinach, and herbs need 6 to 8 inches. Root vegetables like carrots and beets need 10 to 12 inches. Deep-rooted plants like tomatoes and peppers do best in 12 to 18 inches.

A common first bed is 4 feet wide by 8 feet long by 12 inches deep. This size is straightforward to reach across from either side, holds about 32 cubic feet of soil, and fits in most yards. Narrower beds (2 to 3 feet wide) are better if you have limited space or want to reach the center without stepping into the bed.

Taller beds (18 to 24 inches) are easier on your back and knees if you have mobility issues, but they require more soil and cost more to fill. A 4-by-8-foot bed at 18 inches deep needs about 48 cubic feet of soil, which is roughly 1.8 cubic yards.

Assembling the Frame

Cut your boards to length. For a 4-by-8-foot bed, you need two 4-foot pieces and two 8-foot pieces. If you do not have a saw, most lumber yards will make straight cuts for free or a small fee.

Lay the boards on the ground in a rectangle. Check that the corners are square by measuring diagonally from corner to corner—both measurements should be equal. If they are not, adjust the frame until they match.

Fasten the corners. The easiest method is corner brackets—L-shaped metal plates that bolt or screw to the inside of two boards at each corner. Drill pilot holes first to prevent the wood from splitting, then drive 3-inch deck screws through the bracket into each board. You need two brackets per corner (one on each side) for strength.

Alternatively, you can drive 3-inch deck screws directly through one board into the end of the adjacent board, using 3 screws per corner. This method is faster but requires a drill and a bit of practice to keep the boards aligned.

Do not use nails. Screws hold better and are easier to remove if you need to adjust the frame later.

Leveling and Positioning

Once the frame is assembled, place it where you want it to sit permanently. Use a level (a 2-foot or 4-foot level works well) to check that the top edge is level in both directions—lengthwise and widthwise. If the ground slopes, you have two choices: dig out the high side and fill in the low side to level the ground, or build the frame and accept that it will sit slightly tilted.

Most gardeners accept a slight tilt. Soil will settle and shift slightly over the first season anyway. If the tilt is more than 1 inch over the length of the bed, it is worth leveling the ground underneath.

Remove grass and weeds from inside the frame. You can dig them out, or lay cardboard or newspaper over the area and let it smother the grass over a few weeks before filling with soil.

Adding Landscape Fabric and Filling with Soil

Lay landscape fabric (also called weed cloth) across the bottom of the frame. 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 so it does not shift when you add soil.

You can skip the fabric if you removed all the grass and weeds, but it saves work later. Do not use plastic sheeting—it blocks drainage and creates a swamp.

Fill the frame with a mix of soil and compost. A common ratio is 60 percent garden soil and 40 percent compost, but you can adjust based on what you have. Garden soil provides structure and nutrients; compost adds organic matter and improves water retention. Fill to about 1 inch below the top of the frame to leave room for mulch and watering.

The soil will settle over the first few weeks. You may need to add more soil after the first watering and again after a few weeks. This is normal.

Maintenance and When to Replace

Check the frame each spring for rot, especially at the corners and where the wood touches the soil. Poke the wood with a screwdriver—if it sinks in easily, that section is rotting and needs replacement.

Cedar and composite beds rarely need repair if built correctly. Untreated pine beds typically last 3 to 5 years before the bottom boards rot through. When that happens, you can replace just the rotted boards or rebuild the entire frame.

Keep the soil level consistent year to year. If soil washes out during heavy rain, refill it. Over time, compost breaks down and the soil level drops—add fresh compost or soil each spring to maintain depth.

Frequently Asked Questions

Can I build a raised bed on top of grass without removing it first?

Yes. The grass will die and break down under the frame over the first season. Lay cardboard under the frame to speed up the process, or just leave it—the decomposing grass adds organic matter to your soil. You will not have a problem with grass growing up into the bed.

What size should my first raised bed be?

A 4-by-8-foot bed 12 inches deep is a good starting size. It is large enough to grow a variety of plants but small enough to manage without feeling overwhelming. If you have limited space, a 2-by-4-foot bed works just as well.

Do I need to line the bottom of the bed with anything besides landscape fabric?

Landscape fabric is enough. It blocks weeds while letting water drain. Do not use plastic—it traps water and creates soggy soil. If you are worried about burrowing pests like gophers or moles, use hardware cloth (metal mesh) under the fabric, but this is rarely necessary in most gardens.

How much soil do I need to fill a raised bed?

Multiply length × width × depth (in feet), then divide by 27 to get cubic yards. A 4-by-8-foot bed 12 inches deep needs 32 cubic feet, or about 1.2 cubic yards. Most garden centers sell soil by the cubic yard, and many deliver for a fee.

Can I use reclaimed wood from old pallets or fences?

Pallets are risky—you do not know what was stored on them or what chemicals they were treated with. Old fence wood works if it is solid and not rotted, but inspect it carefully. Avoid any wood that was painted or stained, as the finish can leach into soil.