Most store-bought raised bed kits bow outward after their second spring thaw because wet topsoil exerts hundreds of pounds of lateral pressure against thin half-inch planks. When you assemble a garden box, you are building an earth-retention structure, not a picture frame. Investing in rough-sawn dimensional cedar and securing your corners with internal hardwood cleats guarantees that your work survives freezing winter cycles without splitting.
Selecting Rough-Sawn Cedar Over Chemically Treated Lumber
True two-by-eight western red cedar carries natural thujaplicins that inhibit fungal decay and insect damage without the chemical copper treatments found in standard green pressure-treated lumber. Check your local yard for tight-knot architectural rough boards rather than surfaced dimensional stock, as the unplaned face provides extra timber thickness for pocket joinery and resists cupping under direct summer sun.
Locking the Corners with Structural Cleats
Avoid face-screwing end grain directly through exterior planking. Instead, mill four internal corner posts from untreated two-by-four stock, cutting each cleat two inches shorter than your bed depth to keep wood off bare subsoil. Fasten your cedar side walls into these posts using three-inch ceramic-coated exterior structural screws, staggering your fasteners so you never drive two screws along the same grain line.
Ground Preparation and Rodent Exclusion
Level your perimeter footprint down to mineral earth with a flat spade, removing all surface turf to prevent uneven settling under irrigation. Staple a continuous sheet of half-inch galvanized hardware cloth along the bottom edges of the bottom frame before setting it in place, which blocks burrowing rodents while letting earthworms and mycorrhizal fungi migrate freely into your root zone.