What You Need to Build a Raised Bed

A raised garden bed is a wooden or composite box you fill with soil and plant into. Building one yourself costs less than buying a pre-made kit and takes a weekend. You need four boards (usually cedar or composite lumber), corner brackets or screws, a drill, a saw, and a level. Most people spend $40 to $150 on materials, depending on size and wood type.

Cedar lasts 10 to 15 years outdoors without treatment. Composite boards (wood-plastic blend) last 15 to 20 years but cost more upfront. Pressure-treated lumber is cheaper and lasts longer, though some gardeners avoid it because of chemical concerns. Untreated pine is the budget option but rots in 3 to 5 years. Choose based on how long you want the bed to stand and what you are willing to spend.

You do not need expensive tools. A basic cordless drill, a circular saw or handsaw, a level, and a tape measure are enough. If you do not own a saw, most lumber yards will make straight cuts for free or a small fee when you buy the wood.

Key Takeaways

  • Cedar and composite boards last longest (10 to 20 years), while untreated pine rots in 3 to 5 years and pressure-treated wood splits the difference on cost and durability.
  • A basic raised bed needs four boards, corner brackets or deck screws, a drill, and a level — no specialized tools required.
  • Assemble the frame on level ground, check corners with a square, and backfill with soil after the frame is square and stable.
  • A 4-by-8-foot bed 12 inches deep holds about 32 cubic feet of soil and costs $60 to $120 in materials for a cedar frame.

Choosing Your Dimensions and Wood

Standard raised beds are 4 feet wide by 8 feet long by 12 inches deep. This size fits through a standard gate, lets you reach the center from either side without stepping in, and holds enough soil for most vegetables. If you have a small space, 3 by 6 feet or 4 by 4 feet works just as well. Depth matters most for root crops like carrots and potatoes — go 12 inches minimum, 18 inches if you can.

Measure your space and mark where the bed will sit. It should be on level ground or as close as possible. If the ground slopes, you will need to dig out the high side or build up the low side with soil. Sunlight matters more than perfect level — aim for at least 6 hours of direct sun for vegetables, 3 to 4 hours for leafy greens.

For a 4-by-8 bed, buy four boards: two at 8 feet and two at 4 feet. If your lumber yard stocks 6-foot or 10-foot lengths, ask them to cut them to size. Cedar 2-by-12 boards (which are actually 1.5 inches thick and 11.25 inches tall) are the standard choice. Composite boards come in similar sizes and cost 50 to 100 percent more but do not rot.

Assembling the Frame on the Ground

Lay all four boards on the ground in the shape of a rectangle. Do not attach anything yet. Check that the corners are square by measuring diagonally from corner to corner — both diagonals should be the same length. If they are not, nudge the boards until they match. This step prevents a twisted frame that will not sit flat.

Once the frame is square, attach the corners. You have two main options: corner brackets (L-shaped metal pieces bolted to the inside of the boards) or deck screws driven through one board into the end of the other. Brackets are faster and stronger; screws are cheaper. If using screws, drill pilot holes first to prevent splitting, then drive three 3-inch deck screws per corner, staggered vertically.

Flip the assembled frame over and check the bottom for gaps. If the ground is uneven, the frame will rock. Dig out high spots or add soil under low spots until the frame sits flat. This prevents water from pooling and keeps the bed from twisting as it settles.

Positioning and Leveling Your Bed

Move the frame to its final location. Use a level across the length and width to check how far off it is. Most beds do not need to be perfectly level — a slight slope (less than 1 inch over 8 feet) is fine and actually helps drainage. If one corner is more than 2 inches lower than the others, dig out soil under the high corners or add soil under the low ones.

Once the frame is in place and reasonably level, check the corners again with a square. The frame may have shifted during the move. If it is square and stable, you are ready to fill. If it has twisted, loosen the corner fasteners, square it up, and retighten.

If you are building on grass or weeds, lay cardboard or landscape fabric on the ground inside the frame before filling with soil. This blocks weeds from growing up through the bottom and breaks down over time. Cardboard works fine and costs nothing if you have boxes on hand.

Filling and Settling Your Bed

Fill the frame with garden soil or a mix of topsoil and compost. Do not use potting soil — it is too expensive for a large bed. A 4-by-8-foot bed 12 inches deep needs about 32 cubic feet of soil. Most soil is sold by the cubic yard (27 cubic feet), so you will need just over one cubic yard. Bulk soil suppliers deliver for less than bagged soil from a garden center.

As you fill, water the soil lightly and let it settle for a few days. It will compact and drop 1 to 2 inches. Add more soil to bring it back to the top of the frame. Do not pack it down — loose soil drains better and is easier to dig in.

The first year, the soil will settle more as it breaks down and compacts naturally. Top it off in spring before planting. After that, add 1 to 2 inches of compost each year to replace what breaks down and keep the soil level consistent.

Protecting Your Frame From Rot

Cedar resists rot naturally and does not need sealing, though some gardeners explore a food-safe wood stain for appearance. Do not use exterior paint or varnish — it can crack and peel, trapping moisture. Composite boards do not need treatment. Pressure-treated wood should not be sealed because the treatment works best when exposed to air.

The bottom of the frame touches soil and will rot first, regardless of wood type. Lining the inside with landscape fabric or hardware cloth (a metal mesh) slows this. Hardware cloth also keeps burrowing animals like moles and voles out. Staple it to the inside of the frame before filling with soil.

Replace boards as they rot. You do not have to rebuild the whole bed — remove the fasteners at the corners, slide out the rotted board, and slide in a new one. This usually happens to the bottom boards first, after 5 to 10 years depending on wood type and climate.

Common Mistakes to Avoid

Do not skip the squaring step. A twisted frame will not drain evenly, corners will separate, and the bed will look crooked. Spend five minutes checking diagonals before you attach anything.

Do not build on a slope without leveling first. Water will run to the low side, and soil will wash out. A slight slope is fine, but more than 2 inches of drop across the length needs correction.

Do not use untreated pine if you want the bed to last. It rots quickly in wet climates. Cedar or composite is worth the extra cost if you plan to keep the bed for more than five years.

Do not fill with potting soil or garden soil alone. Potting soil is too expensive and drains too fast. Garden soil alone compacts and drains poorly. A mix of topsoil and compost (half and half) works best and costs less.

Frequently Asked Questions

How deep does a raised bed need to be?

Twelve inches is the minimum for most vegetables. Leafy greens and herbs need only 6 to 8 inches. Root crops like carrots, potatoes, and parsnips need 12 to 18 inches to develop properly. If you are growing a mix, go 12 inches and you will be fine for everything except deep-rooting perennials.

Can I use reclaimed wood or pallets?

Pallets work if they are not treated with chemicals (check for "HT" stamped on the wood, which means heat-treated and safe). Reclaimed wood is fine as long as it is not pressure-treated or painted. Avoid wood from old fences or buildings that may have been treated with arsenic or lead paint.

Do I need to line the bottom of the bed?

Lining is optional but helpful. Cardboard blocks weeds and breaks down over two years. Hardware cloth keeps out burrowing animals. Landscape fabric lets water through but slows weed growth. None of these are required, but they reduce maintenance.

How long does it take to build a raised bed?

Assembly takes 30 to 60 minutes if you have tools and the wood is cut to size. Filling takes another hour or two depending on how you get the soil. Leveling and positioning can add time if the ground is very uneven. Plan for a full afternoon or morning.

What is the best soil mix for a new raised bed?

A mix of 50 percent topsoil and 50 percent compost works well and costs less than buying bags of potting soil. Some gardeners use 40 percent topsoil, 40 percent compost, and 20 percent perlite or coarse sand for drainage. The exact ratio matters less than avoiding pure garden soil, which compacts, or pure potting soil, which is too expensive.