A raised garden bed lifts your growing soil above compacted, rocky, or clay-heavy ground and gives you complete control over soil quality, drainage, and access. Building one from cedar takes an afternoon and costs $50 to $100 for a 4x8-foot bed. Cedar is naturally rot-resistant without chemical treatment, making it safe for growing food without worrying about preservative chemicals leaching into the soil.

Build a Garden Raised Bed

Design and Sizing

Width: 4 feet maximum. You need to reach the center from either side without stepping into the bed. Wider beds require stepping on the soil, which compacts it and defeats the purpose.

Length: 8 feet is standard (one board length, minimal cuts). Shorter beds (4x4, 4x6) work for smaller spaces. Longer beds need additional mid-span support to prevent the sides from bowing outward under soil pressure.

Height: 12 inches minimum for most vegetables. 18 to 24 inches for root vegetables (carrots, parsnips, potatoes) and for raised beds on hard surfaces (concrete, gravel) where roots cannot penetrate below the bed.

Materials

For a 4x8-foot bed, 12 inches tall:

• Four cedar 2x12 boards, 8 feet long (two for the 8-foot sides, two ripped or cut for the 4-foot ends and reinforcement)
• Four cedar 4x4 posts, 12 inches long (corner posts)
• 3-inch stainless steel or hot-dip galvanized deck screws (standard steel corrodes against cedar and stains it black)
• Landscape fabric (optional, for the bottom)

Total cost: $60 to $120 depending on local cedar prices.

Alternative materials: Pressure-treated lumber is cheaper ($40 to $60 for the same bed) and lasts longer. Modern ACQ-treated lumber is approved for use around garden beds. Some gardeners prefer cedar for the peace of mind of no chemical treatment near food plants. Both work.

Do not use railroad ties, old telephone poles, or CCA-treated lumber (pre-2004) for garden beds. These contain creosote, pentachlorophenol, or arsenic that leaches into soil.

Cutting

8-foot sides (2 pieces): Use the 2x12 boards at full 8-foot length. No cuts needed.

4-foot ends (2 pieces): Cut from the remaining two 2x12 boards at 45 inches (4 feet minus the combined thickness of the two side boards at the corners — accounting for the side boards overlapping at the corners). Or cut at 48 inches and butt them inside the side boards.

Corner posts (4 pieces): Cut 4x4 cedar into 12-inch lengths (minus 1.5 inches for the board thickness if the posts sit inside the bed). Posts provide rigidity and prevent the corners from spreading under soil pressure.

A circular saw or miter saw handles all cuts. No power tools? A hand saw cuts cedar easily.

Assembly

1. Stand two side boards and two end boards on edge to form the rectangle on a flat surface (driveway, garage floor)
2. Place a corner post inside each corner, flush with the top edges of the boards
3. Pre-drill two screw holes per board into each corner post to prevent splitting
4. Drive 3-inch screws through the side boards into the corner post. Two screws per board face.
5. Drive screws through the end boards into the same corner posts
6. Check for square by measuring diagonals — if both diagonals are equal, the bed is square

For beds taller than 12 inches, stack a second course of boards and add mid-height horizontal cleats or additional vertical posts at the midpoints of the long sides to resist outward bowing.

Site Preparation

1. Choose a location with 6 to 8 hours of direct sunlight
2. Level the ground where the bed will sit. Remove sod if present — a flat-blade shovel works. The bed must sit level; an unlevel bed causes water to pool at one end.
3. Optional: Lay cardboard or landscape fabric under the bed to suppress weeds growing up through the soil. Cardboard decomposes over one season; fabric persists.
4. Position the assembled bed on the prepared site
5. Drive stakes or rebar through the corner posts into the ground for stability if the site is sloped or windy

Filling the Bed

Do not fill a raised bed with garden soil from a bag alone — it compacts too much and drains poorly. Use a mix:

Standard mix:

• 50 percent topsoil or garden soil
• 30 percent compost (homemade or bulk purchased)
• 20 percent perlite, vermiculite, or coarse sand for drainage

Mel’s Mix (Square Foot Gardening method):

• 1/3 compost (from multiple sources)
• 1/3 peat moss or coconut coir
• 1/3 vermiculite

Fill the bed to within 1 inch of the top edge. The soil settles 1 to 2 inches over the first month — add more mix to maintain the level.

A 4x8x1-foot bed holds approximately 32 cubic feet of soil (about 1 cubic yard). Buying soil in bulk (by the cubic yard) from a landscape supply company costs 50 to 70 percent less than buying individual bags.

Enhancements

Drip irrigation: Run a soaker hose or drip line across the bed surface under mulch. Connect to a garden hose with a timer. Consistent, automatic watering produces better results than hand watering and saves time.

Trellis: Attach a vertical trellis to the back (north) side for climbing vegetables — tomatoes, cucumbers, pole beans, peas. Build from cedar 2x2s and wire mesh or string.

Protective mesh: Staple hardware cloth (1/2-inch mesh) to the bottom of the bed before filling to prevent burrowing animals (gophers, moles) from entering from below.

Seat cap: Screw a flat 2x6 cap along the top edges of the bed. This creates a comfortable seat for weeding and provides a surface for setting tools and seed trays.

Maintenance

Cedar raised beds last 8 to 15 years without any treatment. The wood grays naturally. Applying an exterior wood sealer extends the life but is optional.

Each spring:

• Top off the soil with 1 to 2 inches of fresh compost (the soil level drops as organic matter decomposes)
• Check corner joints and tighten or replace screws if loosened by freeze-thaw cycles
• Clear debris and old plant material from the previous season

Bottom Line

A 4x8 cedar raised bed costs $60 to $120 in materials and takes one afternoon to build. Cut four boards, screw them to corner posts, level the site, fill with soil, and plant. It is one of the most satisfying home projects because the results are immediate — you plant the same weekend you build. Stack beds along a sunny fence line and you have a productive garden that stays organized, weed-free, and accessible for years.