What You Need to Build a Raised Bed

A raised garden bed is a wooden frame you build on top of your existing ground. You fill it with soil and grow vegetables, herbs, or flowers inside. The simplest version uses four wooden boards, four corner brackets or screws, a level, and a drill or screwdriver. Most people finish one in an afternoon.

The most common size is 4 feet long, 2 feet wide, and 12 inches tall, though you can adjust these measurements to fit your space. Untreated cedar or composite wood lasts longer than pine, but pine costs less and works fine if you replace it in five to seven years. Avoid pressure-treated wood from before 2004, which contains arsenic; newer pressure-treated wood is safer but still not ideal for vegetables.

You will also need a tape measure, a square to check corners, a drill with a screwdriver bit (or a manual screwdriver), exterior wood screws at least 2.5 inches long, and a level to make sure the frame sits flat. A circular saw or handsaw helps if you need to cut boards to length, but many hardware stores will cut them for you when you buy them.

Key Takeaways

  • A basic raised bed uses four boards, four corner brackets or 16 screws, and takes about two hours to build without power tools.
  • Cedar and composite wood last 10 to 15 years; pine lasts 5 to 7 years and costs half as much.
  • Assemble the frame on level ground, check all corners with a square, and use a level to confirm the whole bed is flat before filling with soil.
  • Screw boards to corner posts or use L-brackets at each corner; both methods are stronger than nails and allow you to disassemble the bed later.

Choosing Wood and Sizing Your Bed

Cedar heartwood resists rot naturally and lasts 10 to 15 years without treatment. It costs more upfront but saves money over time because you will not need to rebuild as often. Composite wood (plastic and wood fiber mixed) lasts even longer, 15 to 20 years, but costs the most and is heavier to move.

Pine boards are the cheapest option and work well for a first bed. They rot faster than cedar, usually in 5 to 7 years, but you can replace them affordably when the time comes. Pressure-treated wood made after 2004 is safe for vegetables and lasts 10 to 12 years, though some gardeners avoid it out of preference.

Standard dimensions are 4 feet by 2 feet by 12 inches tall. This size fits two standard garden rows, is straightforward to reach across, and uses boards you can buy at any hardware store without cutting. If your space is smaller, 3 feet by 3 feet works well and is easier to fill with soil. Taller beds (18 inches) suit people with back pain or those gardening in containers on a patio.

Preparing the Ground and Laying Out Your Frame

Choose a spot that gets at least six hours of direct sun and is relatively level. Remove grass, weeds, and large rocks from the area where the bed will sit. You do not need to dig deep, but clearing the surface helps the frame sit flat and prevents grass from growing up into your soil later.

Lay out your four boards in a rectangle on the ground where you want the bed to be. Use a tape measure to check that opposite sides are equal length and that the diagonals (corner to corner) are equal too. If the diagonals match, your corners are square. Adjust the boards until they form a true rectangle, then mark the corners with chalk or a stick so you know where to place fasteners.

Place a level along each side of the frame. If the ground slopes, you have two choices: shim the frame with shims or gravel so it sits level, or accept a slight slope and fill the bed with extra soil on the low end. A level bed drains and waters more evenly, so it is worth taking time to get it right.

Fastening Corners with Screws or Brackets

The strongest method uses exterior wood screws driven through the face of one board into the end grain of the adjacent board. Drill a pilot hole first (a small hole that guides the screw and prevents splitting), then drive a 2.5-inch or 3-inch screw through the pilot hole. Use four screws per corner, spaced about 2 inches apart vertically, for a bed that will last years without wobbling.

If you prefer not to drill, L-brackets bolted to the outside corners work equally well. Attach one bracket per corner using bolts, washers, and nuts; tighten with a wrench. Brackets are visible from outside the bed but make disassembly easier if you ever want to move or rebuild.

A third option is corner posts: 4x4 wooden posts cut to the height of your bed, with boards screwed to the sides of the posts. This method is overkill for a small bed but gives you a very sturdy frame and looks finished. It also uses more wood and costs more.

Checking Square and Level Before Filling

After fastening all four corners, measure both diagonals again. They should be exactly equal. If they are not, the frame is racked (twisted), and you need to loosen fasteners and adjust until the diagonals match. This step takes five minutes and prevents a wobbly bed that shifts as you walk around it.

Place a level along the length and width of the frame. The bubble should sit in the center of the level tube. If one end is higher, you can shim it with gravel or soil, or you can accept a slight slope if it is less than an inch over 4 feet. Most gardeners do not notice a slope that small, and plants grow fine on it.

Once the frame is square and level, walk around it and push on each side. It should feel solid with no flex or movement. If it moves, tighten fasteners or add more screws. A rigid frame prevents soil from spilling out and keeps the bed usable for years.

Adding a Landscape Fabric Liner (Optional)

A landscape fabric liner sits inside the frame and blocks weeds from growing up from the ground below. It is optional but saves weeding time, especially in the first year. Lay the fabric flat inside the frame, overlapping seams by 6 inches, and staple it to the inside top edge of the boards. Trim excess fabric with a utility knife.

Do not use plastic sheeting; it traps water and kills soil organisms. Landscape fabric (also called weed cloth) lets water through while blocking weeds. It costs five to ten dollars for a bed this size and lasts two to three years before breaking down.

If you skip the liner, you will likely see weeds in the bed by mid-summer, especially if the ground below was weedy. Pulling them is not difficult, but a liner makes the first season much easier.

Filling and Planting Your Bed

A 4-by-2-by-12-inch bed holds about 8 cubic feet of soil, which is roughly one cubic yard. You can buy bagged garden soil, potting mix, or a blend of topsoil and compost. Bagged soil costs more per cubic foot but is easier to transport and handle. Bulk soil delivered by truck costs less but requires a truck to unload it.

Fill the bed to within an inch of the top. The soil will settle over the first few weeks, so do not fill it completely. Water the bed thoroughly after filling; this helps soil settle and removes air pockets. Wait a few days, then add more soil if the level drops noticeably.

You can plant when ready after filling, though the soil will continue to settle for several weeks. If you are planting seeds, wait until the soil has settled completely so seeds do not sink deeper than intended. Transplants (seedlings or small plants) can go in right away.

Frequently Asked Questions

How deep should a raised bed be?

Twelve inches is the standard minimum for most vegetables. Root vegetables like carrots and beets need 12 inches; leafy greens need 8 inches; tomatoes and peppers need 12 to 18 inches. If you are growing only shallow-rooted plants like lettuce or herbs, 8 inches works, but 12 inches gives you more flexibility.

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

Yes, but grass will grow up through the soil and into your bed for the first year or two. Removing the grass first saves weeding time later. If you leave it, lay cardboard or newspaper over the grass before filling the bed; this smothers the grass and breaks down over time.

What is the best wood for a raised bed in a wet climate?

Cedar heartwood or composite wood resist rot best in wet conditions. Pressure-treated wood made after 2004 also works well. Avoid pine in very wet climates; it rots in three to four years instead of five to seven. Cedar costs more but lasts twice as long, so it is the better choice if you want to avoid rebuilding often.

Do I need to treat the wood with sealant or stain?

No. Sealants and stains can leach chemicals into soil and are unnecessary for cedar or pressure-treated wood. These woods are already treated to resist rot. Leaving them bare and letting them weather naturally is fine and keeps your soil clean.

How long does it take to build a raised bed?

One to two hours for a single bed, depending on whether you drill pilot holes and how carefully you check for square and level. If you are building multiple beds, the second and third go faster because you develop a rhythm. Most of the time is spent checking measurements and fastening corners, not assembly itself.