What You Need Before You Start
A raised bed garden is a wooden or composite box filled with soil, sitting on top of your existing ground. To build one, you need four pieces of lumber (or composite boards), corner brackets or screws, a drill or screwdriver, a level, and a saw if you are cutting boards to length. Most people also add landscape fabric to the bottom to block weeds, and a shovel to fill it with soil.
The most common size is 4 feet by 8 feet by 12 inches deep, which fits two standard bags of soil and is straightforward to reach across without stepping inside. You can build smaller or larger, but anything wider than 4 feet means you cannot reach the center from either side without stepping on the soil, which compacts it and damages plant roots.
Untreated cedar or composite boards last longest — cedar naturally resists rot for 10 to 15 years, while composite lasts 20 years or more. Pressure-treated lumber is cheaper but contains chemicals that can leach into soil over time, so avoid it for vegetable gardens. Avoid railroad ties entirely; they are soaked in creosote, a known toxin.
Key Takeaways
- A raised bed is a wooden box 4 feet by 8 feet by 12 inches deep, built from untreated cedar or composite boards and filled with soil.
- You assemble it on level ground using corner brackets or deck screws, then line the bottom with landscape fabric to stop weeds.
- Fill it with a mix of topsoil and compost, not garden soil alone, because garden soil compacts and drains poorly in a confined space.
- A standard 4-by-8 bed costs between $150 and $400 depending on board material, and holds enough soil for 16 to 20 vegetable plants.
Choosing Your Location and Preparing the Ground
Place your raised bed where it will get at least six hours of direct sun per day — most vegetables need this to produce well. Avoid spots under tree branches or next to fences that cast afternoon shade. The ground does not have to be perfectly level, but it should be relatively flat; a slope of more than a few inches means water will pool on one side and dry out on the other.
Clear the area of grass, weeds, and large rocks. You do not need to remove every stone, but pull out anything bigger than your fist. If the ground is very compacted or has poor drainage, loosen the top 2 to 3 inches with a garden fork before you place the bed. This helps water drain through the bottom and lets roots eventually reach deeper soil.
Building the Frame and Securing the Corners
Cut your boards to length if needed — a 4-by-8 bed uses two 8-foot boards and two 4-foot boards. Lay them on the ground in a rectangle and check that the corners are square by measuring diagonally from corner to corner; both measurements should be equal. Adjust the corners until they match.
find the corners with either galvanized corner brackets (bolted or screwed on the inside) or 3-inch deck screws driven through one board into the end of the adjacent board. Brackets are faster and more reliable; screws are cheaper but require a drill and a steady hand. Use at least two fasteners per corner so the frame does not rack (twist) when filled with wet soil.
Once the frame is assembled, place a level across the top in both directions and adjust the ground underneath until the bed is level. A bed that tilts will cause water to run off one side and leave the other dry.
Lining the Bottom and Adding Soil
Lay landscape fabric across the bottom of the bed, overlapping the seams by 6 inches. This blocks weeds from growing up through the bottom while still letting water drain. Staple it to the inside of the boards so it does not shift when you add soil. You do not need expensive weed cloth; basic landscape fabric from a hardware store works fine and costs a few dollars.
Fill the bed with a mix of topsoil and compost — aim for roughly 60 percent topsoil and 40 percent compost by volume. Do not use garden soil alone; it compacts in a raised bed and drains poorly. A standard 4-by-8-by-12-inch bed holds about 32 cubic feet of soil, which is roughly 1.2 cubic yards. Most garden centers sell soil by the cubic yard or in bags; a 2-cubic-foot bag is easier to handle but costs more per volume than bulk soil delivered by truck.
Water the soil as you fill so it settles and compacts naturally. The soil level will drop over the first week as it settles further; add more if needed so you have at least 10 inches of soil depth for most vegetables.
Cost and Material Comparison
A 4-by-8-foot raised bed built from untreated cedar boards costs roughly $200 to $250 for the lumber alone, plus $30 to $50 for corner brackets or screws, and $100 to $150 for soil and compost. Total: $330 to $450. Composite boards cost more upfront — $300 to $350 for the frame — but last twice as long, so the cost per year is lower if you plan to keep the bed for many years.
Smaller beds (3-by-6 or 2-by-4) cost less but hold fewer plants and require more frequent watering because they dry out faster. Larger beds (4-by-12) hold more soil but are harder to reach across and use more material. A 4-by-8 bed is the best balance for most home gardeners.
If budget is tight, start with one bed and add more the following year. A single bed produces enough vegetables for one person or a couple through much of the growing season.
Maintenance and Long-Term Care
Check the frame each spring for rot or loose fasteners. Cedar boards will gray over time but remain structurally sound for years. If a board begins to split or crack, you can replace just that board without rebuilding the whole bed — unbolt or unscrew the corners, slide the damaged board out, and slide a new one in.
The soil will settle and compress over time as organic matter breaks down. Add 1 to 2 inches of compost each spring to maintain depth and fertility. After five to seven years, the original soil may be depleted; at that point, you can either replace the top 6 inches with fresh compost or empty the bed entirely and refill it.
Landscape fabric at the bottom will eventually degrade, usually after five to ten years depending on sun exposure. You do not need to replace it unless weeds start coming up through the bottom; if that happens, you can add a new layer on top of the old one without emptying the bed.
Frequently Asked Questions
Can I build a raised bed on concrete or pavement?
Yes, but drainage becomes critical. Drill or drill holes in the landscape fabric so water can drain out the bottom, or skip the fabric entirely and accept that some weeds may grow up from cracks. Soil will dry out faster on concrete, so plan to water more often.
What size should I make my first raised bed?
Start with 4 feet by 8 feet by 12 inches deep. It is large enough to grow 16 to 20 plants, small enough to manage, and fits standard lumber sizes so you waste nothing. If you have limited space, a 3-by-6 or 2-by-4 bed works, but anything narrower than 2 feet is awkward to fill and plant.
Do I need to add a bottom to my raised bed?
No. An open bottom lets roots grow deeper into native soil and improves drainage. A solid bottom (wood or plastic) prevents root growth and can trap water, causing rot. Landscape fabric alone is enough to stop weeds.
How deep should the soil be for vegetables?
Most vegetables need 10 to 12 inches of soil depth. Shallow-rooted crops like lettuce and spinach can grow in 8 inches; deep-rooted crops like tomatoes and carrots need 12 to 18 inches. A 12-inch-deep bed is a good compromise for a mixed vegetable garden.
Can I use old wood or reclaimed boards?
Only if you know what the wood was treated with. Reclaimed lumber from old buildings or fences may contain lead paint or unknown chemicals. Untreated or naturally rot-resistant wood (cedar, redwood, black locust) is safe; pressure-treated or painted wood is not worth the risk in a vegetable garden.