What You Need to Build a Raised Bed
A wood raised bed is a wooden box you fill with soil and plant in. You can build one in a weekend with basic tools and materials you can buy at any home center. The most common size is 4 feet by 8 feet by 12 inches deep, though you can make yours smaller or larger depending on your space and how much you want to lift when you're planting.
You will need untreated wood boards (cedar, composite, or redwood last longest), wood screws, a drill, a level, and a saw if you're cutting boards to length. You do not need concrete footings or a foundation—a raised bed sits directly on the ground. The soil weight holds it in place.
Avoid pressure-treated wood from before 2004, which contains arsenic. Pressure-treated wood made after 2004 is safe for vegetable gardens. Cedar and composite boards cost more but last 10 to 15 years instead of 5 to 8. Untreated pine is the cheapest option and will rot in 3 to 5 years, but it works fine if you're willing to replace it.
Key Takeaways
- A basic raised bed uses four boards screwed together at the corners, no digging or foundation required.
- Cedar and composite boards last 10 to 15 years; untreated pine lasts 3 to 5 years and costs less.
- You can build a 4-by-8-foot bed in two to three hours with a drill, level, and saw.
- Set the bed on level ground, fill it with soil, and water it down before planting so the soil settles.
Choosing Your Wood and Sizing Your Bed
The wood you choose affects how long your bed lasts and how much you spend. Cedar is naturally rot-resistant and looks good, but costs $3 to $6 per board foot. Composite boards (wood fiber mixed with plastic) last the longest and don't rot, but cost $5 to $8 per board foot. Pressure-treated lumber made after 2004 is safe and costs $1 to $3 per board foot. Untreated pine is cheapest at $0.50 to $1.50 per board foot but rots fastest.
For a 4-by-8-foot bed that is 12 inches deep, you need two 8-foot boards and two 4-foot boards, all 2 inches thick and 12 inches tall. If your home center doesn't stock 12-inch boards, you can buy 2-by-10 boards (which are actually 9.5 inches tall) and add a 2-by-2 board on top of each side. A 4-by-4-foot bed uses four 4-foot boards and takes up less space. A 2-by-4-foot bed is good for a patio or small yard.
Depth matters for what you grow. Lettuce and herbs need 6 to 8 inches. Tomatoes, peppers, and carrots need 12 inches. Root vegetables like potatoes need 18 inches. If you're growing a mix, 12 inches is the practical middle ground.
Preparing the Ground and Assembling the Frame
Choose a spot that gets at least six hours of direct sun for vegetables. Clear away grass, weeds, and large rocks. You do not need to dig down or remove the sod—the soil in your bed will sit on top of it. If the ground is very uneven, remove the high spots with a shovel so the bed sits mostly level.
Lay out your boards in a rectangle on the ground where you want the bed. Check that the corners are square by measuring diagonally from corner to corner—both measurements should be the same. Adjust the boards until they match.
Drill pilot holes (small starter holes) through the end of one board into the end of the adjacent board at each corner. Use three 3-inch wood screws per corner, spaced a few inches apart vertically. Screw them in with a drill set to medium speed. Do not use nails—they will loosen as the wood shifts and the bed will rack (twist out of square).
Once all four corners are screwed, place a level on the inside of the bed and check that it is level side to side and front to back. If one corner is high, you can shim it (slip a shingle or thin board under it) or dig out soil underneath. A slightly unlevel bed is fine; perfectly level is not necessary.
Filling and Settling Your Bed
Before you add soil, lay landscape fabric or cardboard on the ground inside the bed. This blocks weeds from growing up through the bottom. Cardboard breaks down over time and is fine; landscape fabric lasts longer. Staple it to the inside of the boards so it stays in place.
Fill the bed with a mix of topsoil and compost. A common ratio is half topsoil and half compost, though you can adjust based on what you have available. For a 4-by-8-foot bed that is 12 inches deep, you need about 32 cubic feet of soil, which is roughly 1.2 cubic yards. Most soil is sold by the cubic yard, so order 1.5 cubic yards to account for settling and waste.
Dump the soil into the bed and spread it evenly with a shovel. Water it thoroughly with a hose until water runs out the bottom. The soil will settle over the next few days as the water drains. Add more soil if the level drops below the top of the boards. After a week, the soil will have settled to its final level and you can plant.
Tools and Materials Checklist
| Item | Quantity (4x8 bed) | Notes |
|---|---|---|
| 2x12 boards (untreated, cedar, or composite) | 2 at 8 feet, 2 at 4 feet | Or use 2x10 boards plus 2x2 trim boards |
| 3-inch wood screws | 12 screws | 3 per corner; use exterior-grade screws |
| Landscape fabric or cardboard | 1 roll or 4-5 sheets | Covers the bottom to block weeds |
| Topsoil and compost mix | 1.5 cubic yards | Accounts for settling; adjust for bed size |
| Drill with bits | 1 | For pilot holes and driving screws |
| Level | 1 | 2 to 4 feet long; checks if bed is square |
| Saw (circular or hand) | 1 | Only needed if cutting boards to length |
Common Mistakes to Avoid
Using nails instead of screws is the most common mistake. Nails loosen as the wood shifts with temperature and moisture changes, and the bed will rack and leak soil. Screws hold tight and can be tightened again if needed.
Buying pressure-treated wood from before 2004 is a real concern if you're growing vegetables. Older pressure-treated lumber contains chromated copper arsenate (CCA), which can leach into soil. Lumber treated after 2004 uses copper-based preservatives and is safe. Check the label or ask the home center staff when the lumber was treated.
Placing the bed in shade or part shade will slow growth and reduce yields. Vegetables need at least six hours of direct sun. If your yard is shaded, choose a sunnier spot or grow shade-tolerant crops like lettuce and spinach.
Overfilling the bed with soil so it overflows when you water wastes soil and makes the bed harder to work in. Fill it to about an inch below the top of the boards.
Maintaining Your Raised Bed Over Time
Each year, add 1 to 2 inches of compost to the top of the bed. This replaces nutrients the plants used and keeps the soil rich. You do not need to replace all the soil—just top it off.
Check the boards every spring for rot, especially the bottom corners where wood meets soil. Cedar and composite boards rarely rot. Pressure-treated boards may show soft spots after 5 to 8 years. If rot is only on the surface, you can scrape it out and treat it with a wood preservative. If the rot goes deep or affects the structural corners, replace that board.
Tighten screws if the bed starts to rack or if you notice gaps opening at the corners. Use a drill to drive them in a quarter turn at a time until they are snug. Do not over-tighten, which can strip the wood.
Frequently Asked Questions
Do I need to put a bottom on the raised bed?
No. A solid bottom would trap water and cause rot. Landscape fabric or cardboard on the ground blocks weeds but lets water drain. If you have a serious gopher or mole problem, you can line the bottom with hardware cloth (a metal mesh), but this is not necessary for most gardens.
Can I use old pallets to build a raised bed?
Pallets work if they are made of untreated wood and were not used to ship chemicals or treated materials. Pallets that held food or non-hazardous goods are usually safe. Avoid pallets stamped with "HT" (heat-treated) or "MB" (methyl bromide), which indicate chemical treatment. Pallets are often shorter than 12 inches, so you may need to stack two or add trim boards.
How deep should a raised bed be for growing vegetables?
Shallow-rooted crops like lettuce, spinach, and herbs need 6 to 8 inches. Medium-rooted crops like tomatoes, peppers, and beans need 10 to 12 inches. Deep-rooted crops like carrots, beets, and potatoes need 12 to 18 inches. A 12-inch bed works for most mixed vegetable gardens.
What should I fill the bed with if I don't want to buy soil?
You can layer materials in a lasagna-bed style: cardboard on the bottom, then leaves, grass clippings, kitchen scraps, and compost in alternating layers. Over time, these break down into soil. This works but takes longer to settle and may not be as rich as purchased topsoil and compost mixed together. It is a good option if you have free materials available.
Can I build a raised bed on concrete or a patio?
Yes, but water will not drain through the concrete, so the soil will stay wet. Drill or drill-and-tap holes in the concrete bottom of the bed to let water escape, or build the bed with a solid wood bottom and drill drainage holes in that. Alternatively, use a raised bed with a built-in drainage layer or grow in containers instead.