The basic steps to build a raised bed
A raised planting bed is a bottomless box you fill with soil and plant into. You build it by choosing a location, assembling four sides from wood or composite material, securing the corners, and filling it with soil. The whole job takes two to four hours for a standard 4-by-8-foot bed, and you need only basic tools: a drill, a saw (or have the lumber yard cut your boards), a level, and a tape measure.
The most common approach is to use untreated wood boards stacked and fastened at the corners with screws or bolts. Cedar and redwood resist rot longer than pine, but any untreated lumber will work—treated lumber is no longer recommended for vegetable beds because the preservatives can leach into soil. Composite materials like recycled plastic lumber cost more upfront but last 15 to 20 years instead of 5 to 10.
Key Takeaways
- Untreated wood boards fastened at the corners with deck screws is the fastest and cheapest method for most home gardeners.
- Cedar and redwood last longer than pine, but any untreated lumber works; treated lumber should not be used for vegetable beds.
- A level bed prevents water from pooling in one corner, so check your ground before you fill it and adjust the frame if needed.
- Filling a 4-by-8-foot bed 12 inches deep requires about 32 cubic feet of soil, which you can calculate for your own dimensions using length × width × depth.
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. Check that water drains away after rain—if the ground stays soggy, the bed will too. Avoid areas directly under trees, where roots will compete with your plants and falling leaves will clog the bed.
Clear away grass, weeds, and debris from the footprint. You do not have to remove the sod entirely, but pull up any large clumps so the frame sits flat. If the ground is very uneven, you can level it by removing high spots and filling low spots with soil, or you can build the frame and shim it level with shims or soil underneath. Use a level to check—a bed that tips even slightly will cause water to pool on the low side.
Selecting and cutting your materials
For a standard 4-by-8-foot bed, you need two 8-foot boards and two 4-foot boards. Most people use 2-by-12 lumber (which is actually 1.5 inches thick and 11.25 inches tall), giving you about 10 inches of planting depth after the frame sits on the ground. If you want deeper soil for root vegetables, use 2-by-14 or stack two layers of 2-by-12 boards.
Untreated cedar and redwood are sold at most lumber yards and cost roughly 50 to 100 percent more than pine, but they resist rot for 10 to 15 years instead of 5 to 7. Composite lumber costs two to three times as much as pine but lasts 15 to 20 years and requires no maintenance. If you choose pine, expect to replace boards in five to seven years as they rot at the corners and base.
Have the lumber yard crosscut your boards to length if you do not have a saw at home. Bring your measurements written down so you get the right lengths the first time.
Assembling the frame and securing the corners
Lay the four boards on the ground in a rectangle. Drill pilot holes (small starter holes) at each corner to prevent the wood from splitting when you drive screws in. Use 3-inch deck screws—at least three per corner, one near the top, one near the middle, and one near the bottom. Deck screws hold better than nails and are easier to remove if you need to adjust the frame later.
Alternatively, you can use corner brackets (metal L-shaped fasteners bolted to the inside of the frame) or lag bolts drilled through the boards. Brackets are the easiest for beginners and cost $5 to $15 per corner. Lag bolts are stronger but require a drill bit sized to the bolt diameter and take longer to install.
Once the corners are fastened, place the frame where you want it and check it with a level in both directions. If one corner is high, you can either dig out soil underneath it or add soil under the low corners. Adjust until the frame is level or slopes very slightly toward one side for drainage.
Calculating and adding soil
Multiply the length, width, and depth of your bed to find the cubic feet of soil you need. A 4-by-8-foot bed that is 12 inches (1 foot) deep needs 32 cubic feet of soil. Soil is sold by the cubic yard (27 cubic feet), so you would order about 1.25 cubic yards, which is usually rounded up to 1.5 cubic yards to account for settling.
You can buy bagged soil from a garden center or order bulk soil delivered. Bulk soil is cheaper per cubic foot but requires a truck or trailer to haul it. Bagged soil is convenient for small beds but adds up quickly for large ones. Many gardeners use a mix: bulk topsoil or garden mix as the base, topped with a few inches of bagged compost or potting soil for better drainage and nutrients.
Spread the soil evenly and rake it level. Water it lightly and let it settle for a day or two before planting. The soil will compact over time, so you may need to add more after the first season.
Preventing pests and extending bed life
If you are concerned about burrowing pests like gophers or moles, line the bottom of the bed with hardware cloth (a metal mesh) before adding soil. Staple it to the underside of the frame so it does not shift. This adds cost and labor but is effective in areas with heavy pest pressure.
To extend the life of wood boards, you can line the inside with landscape fabric or plastic sheeting to slow rot. Staple it to the frame so it does not sag into the soil. This is optional and does not prevent rot entirely, but it can add a year or two to the frame's life. Do not use plastic if you are concerned about moisture retention—fabric breathes better.
Common mistakes and how to avoid them
The most common mistake is building on uneven ground and not checking with a level. Water will pool on the low side, and plants on the high side will dry out faster. Spend five minutes leveling the ground before you fasten the corners.
Another mistake is using treated lumber for vegetable beds. Older treated lumber contained arsenic, which is no longer used, but modern treatments still contain copper compounds that can leach into soil over time. Stick with untreated wood or composite materials.
A third mistake is filling the bed with only topsoil. Topsoil alone compacts and drains poorly. Mix in compost or aged manure (about one-third compost to two-thirds topsoil) so plants have better drainage and more nutrients. You can add more compost as a top layer each spring.
Frequently Asked Questions
How deep should a raised bed be?
Most vegetables need 8 to 12 inches of soil. Root vegetables like carrots and parsnips need 12 inches or more. Leafy greens and herbs can grow in 6 to 8 inches. A 2-by-12 board gives you about 10 inches of usable depth, which works for most gardens.
Can I build a raised bed on top of grass?
Yes. The grass will die under the frame and decompose into the soil, adding organic matter. Pull up large clumps of sod so the frame sits flat, but you do not need to remove all the grass. The bed will settle slightly as the grass breaks down, so fill it a little higher than you want the final level to be.
What size raised bed should I build?
A 4-by-8-foot bed is standard because it is large enough to be useful but narrow enough that you can reach the center from either side without stepping into it. Smaller beds (3-by-6 or 2-by-4) work well for patios or tight spaces. Avoid beds wider than 4 feet unless you plan to step into them, because you will compact the soil reaching across.
Do I need to put anything on the bottom of the raised bed?
No, unless you have gophers or moles. A bottomless bed lets roots grow into the native soil below and allows water to drain. If you line the bottom with plastic, water will pool and roots will rot. Hardware cloth stops burrowing pests but still lets water drain and roots grow down.
How often do I need to replace the boards?
Untreated pine lasts five to seven years before rot becomes a problem at the corners and base. Cedar and redwood last 10 to 15 years. Composite lumber lasts 15 to 20 years. You can extend the life of wood by lining the inside with landscape fabric, which slows (but does not stop) rot.