Suzanne Williamson, RD
Registered dietitian and founder of Frugal Organic Mama. I've built seven raised beds over the past decade — three cedar, two pine (both rotted within five years), one galvanized steel, and one experimental hugelkultur bed. Each one taught me something. The cedar beds I built nine years ago still look good. The pine ones are gone.
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Building a raised bed is one of the most straightforward home garden projects — the concept is simple, the tools required are minimal, and the result is immediately usable. Where people get tripped up is usually in three places: wood choice, depth, and what to do with the ground underneath.
I've made all three mistakes at various points. This guide is what I'd tell myself before building the first one.
Wood Choice: The Decision That Determines How Long Your Bed Lasts
This is where the most consequential decision gets made, and where the most misleading advice circulates.
Cedar: The Right Answer for Most Situations
Cedar contains natural oils — primarily thujaplicins — that make it toxic to the fungi responsible for wood rot. Untreated cedar in direct soil contact lasts 10–20 years depending on climate and rainfall. In wet climates, closer to 10. In dry climates, 20 is realistic.
Western red cedar is the most widely available variety in North America. It's relatively lightweight, easy to work with standard tools, takes screws without splitting if you pre-drill, and is safe for food gardens with no chemical treatment.
Cost: At current lumber prices, a 4×8×12-inch bed using 2×6 cedar runs approximately $55–80 depending on region. This is the most significant upfront cost difference compared to pine. Over a 15-year lifespan, cedar costs $4–5 per year. Pine that lasts 4 years costs $6–10 per year after you factor in replacement.
What to Avoid and Why
Pine and untreated fir: These work and are inexpensive ($20–35 for the same 4×8 bed). They will rot in 3–5 years in direct, moist soil contact. If budget is the primary constraint, pine is fine — just expect to rebuild.
Pressure-treated lumber: This requires more explanation than most guides provide. Modern pressure-treated lumber uses copper-based preservatives (ACQ — alkaline copper quaternary, or CA-B — copper azole) to replace the arsenic-based treatments phased out in 2003. These are less toxic than the old formulations, but copper does leach into surrounding soil, particularly in acidic conditions.
Studies measuring soil copper levels adjacent to raised beds built with ACQ-treated lumber have found elevated copper at the soil-wood interface. Copper at elevated concentrations is toxic to earthworms and soil microorganisms — exactly the organisms that make garden soil productive. For ornamental beds, this is a minor concern. For food gardens, I don't use it.
If you see lumber labeled "Ground Contact" or "Above Ground" with a green tint — that's pressure-treated. Check the tag attached to the lumber for the specific treatment type.
Railroad ties: Treated with creosote, a coal tar derivative that is a known carcinogen. Not appropriate near food plants under any circumstances.
Composite lumber: Made from wood fiber and recycled plastic. Doesn't rot, looks clean, but is expensive ($150–300 for the same bed), difficult to cut without special blades, and the plastic content raises questions about leaching that haven't been thoroughly studied for food garden applications.
Galvanized steel kits: A legitimate option. Galvanized steel doesn't rot, is easy to assemble, and modern food-grade galvanized steel poses minimal zinc leaching concern. The look is different from wood — more industrial. Cost runs $80–200 for a 4×8 kit. Lifespan is essentially unlimited.
Dimensions: What Size Actually Makes Sense
Width: 4 Feet Maximum
The reason for the 4-foot standard: you can reach the center of a 4-foot wide bed from either side without stepping in. This is the entire point of raised beds for many gardeners — you never compact the soil by stepping on it. A 5-foot wide bed requires stepping in to reach the center, defeating the purpose.
If the bed is against a wall or fence and accessible from only one side, reduce to 2 feet.
Length: Flexible, But Think About Materials
8 feet works with standard lumber dimensions without cuts on the long sides — an 8-foot 2×6 board forms one complete long wall. 4-foot and 12-foot lengths also work with standard lumber without waste.
Odd lengths (7 feet, 10 feet) require cuts that create waste. The lumber yard will cut for you, but design around standard lengths when possible.
Depth: More Than You Think
6 inches: Too shallow for most vegetables. Fine for lettuce, herbs, radishes, and shallow-rooted flowers. Roots will hit the native soil beneath — if the native soil is hard clay or compacted, growth will be limited.
12 inches: The practical standard. Accommodates the root depth of almost all common vegetables including tomatoes, peppers, carrots (short varieties), and squash. This is what I build.
18 inches: Eliminates concerns about native soil quality. Roots stay entirely within the raised bed mix. Useful when native soil is very poor, heavily compacted, or potentially contaminated. Also allows growing full-length carrot varieties (Nantes, Imperator types) without interference.
24 inches: Used for accessibility — raised enough that gardening doesn't require bending. Common in therapeutic gardens and for gardeners with mobility limitations. Requires significantly more soil and support structure.
The Material List for a Standard 4×8×12-Inch Bed
| Material | Quantity | Approx. cost | Notes |
|---|---|---|---|
| Cedar 2×6, 8 feet | 4 boards | $48–72 | 2 boards uncut for long sides; 2 boards cut to 45" for short ends |
| 3" exterior screws | 1 lb box | $8–12 | Stainless or coated for corrosion resistance; you'll use ~24 |
| Cardboard | Free | $0 | Appliance boxes, grocery store boxes — ask retailers |
| Total (before soil) | $56–84 | Cedar, 12" depth, no corner brackets needed |
Optional additions:
Corner brackets ($10–15 for a set of four) make assembly faster and add rigidity. Not necessary if the screwed corners are well-made, but useful for larger beds (12+ feet) or if you're building multiple beds and want consistency.
Ground stakes ($5–10) driven through the bed frame into the ground at the corners prevent the bed from shifting on sloped sites or in high-wind areas.
Assembly: Two Hours, One Tool
You need a drill with a Phillips screwdriver bit. That's the only power tool required. A miter saw makes cleaner cuts, but the lumber yard will cut for you.
Step 1: Get the short end boards cut.
If you're using 8-foot 2×6 boards for all four walls: the two long sides are 8 feet each (no cut needed). The two short ends need to be 45 inches — 48 inches (4 feet) minus 1.5 inches for each of the two side boards that will overlap them. Ask the lumber yard to make these cuts. Most do it free or for $0.50–1 per cut.
Step 2: Pre-drill corner holes.
Before screwing, drill pilot holes slightly smaller than your screw diameter through the long side boards at each corner — three holes per corner, spaced evenly. Pre-drilling prevents cedar from splitting, which it will do without this step at the ends of boards.
Step 3: Assemble on a flat surface.
Lay the two long side boards parallel on a flat surface, 45 inches apart (inside measurement). Butt a short end board against the inside of each end, flush with the top and bottom of the long boards. Drive three screws through the long board into the end grain of the short board at each corner.
Cedar end-grain doesn't hold screws as strongly as face grain — three screws per corner, angled slightly toward the center of the short board, provides adequate holding power. If you want more rigidity, add corner brackets on the inside.
Step 4: Check square.
Measure diagonally from corner to corner in both directions. If the measurements are equal, the frame is square. If not, push one corner gently until the diagonals match, then add a temporary brace (a scrap of wood across a corner) while the structure sets.
Step 5: Position and level.
Carry the assembled frame to its final location. Set it down and check level with a 4-foot level on both long sides and across the width. A slight out-of-level (under 2 inches across 8 feet) is acceptable — water will pool on one side but not catastrophically. If significantly out of level, dig down slightly on the high side rather than shimming up the low side.
Step 6: Cardboard and soil.
Lay overlapping sections of cardboard inside the frame, covering the entire bottom and extending 6 inches out from the walls in all directions. Remove all tape and staples — these don't decompose. Wet the cardboard thoroughly with a hose. The cardboard suppresses existing vegetation and decomposes into organic matter within one season. Fill with soil mix.
What to Plant and When
A freshly built raised bed can be planted immediately — there's no curing time needed for cedar, and the soil mix is ready from the first day.
For what to plant in a new raised bed, how to sequence crops through the season, and companion planting basics, see What to Plant in a Raised Bed in Your First Year.
For the soil mix that goes into the bed, see Best Soil Mix for Raised Beds — the right ratio of compost, topsoil, and amendments makes a larger difference than any other variable in raised bed productivity.
Ready to fill your new bed?
Enter your bed dimensions and the soil calculator tells you how many cubic feet you need — and how many bags to buy.
The Long-Term Cost Picture
A well-built cedar raised bed lasts 10–20 years. Over that period, the $60–80 construction cost works out to $3–5 per year before soil — less than a bag of potting mix annually.
The ongoing costs are soil amendments (compost added each season, roughly $10–20 per bed per year), seeds or transplants, and water. The structure itself requires essentially no maintenance once built. I've never sealed, painted, stained, or treated any of my cedar beds — they gray naturally and remain structurally sound.
The productivity return depends on what you grow and local food prices. A 4×8 bed in a good year can produce $200–400 in fresh vegetables at retail prices — tomatoes, peppers, lettuce, and herbs are the highest-value crops per square foot. Even at lower yields, the math typically favors building.
Related Reading
- Best Soil Mix for Raised Beds — The right ratio of compost, topsoil, and amendments for productive raised bed soil
- How Much Does It Cost to Fill a Raised Bed? — Full cost breakdown for every soil approach from budget to premium
- Raised Bed Soil Depth: How Deep Does Your Bed Really Need to Be? — The depth requirements for every vegetable category
- Hugelkultur Raised Bed Guide — The wood-core raised bed method that reduces watering and builds soil over time
- What to Plant in a Raised Bed in Your First Year — Crop selection and sequencing for a new raised bed
