How to Build a Raised Garden Bed

Pick a spot that gets at least 6-8 hours of direct sunlight per day — most vegetables and herbs need full sun to thrive. Avoid low-lying areas where water pools after rain, and stay at least 2 feet away from fences or walls so air circulates around your plants. Make sure you can reach the center of the bed from both sides — a 4-foot width is ideal because you can reach 2 feet in from each side without stepping on the soil. Place the long side facing south if possible, so all plants get even sun exposure.

For a 4x8-foot bed that's 12 inches deep (two boards high), you need: four 8-foot lengths and four 4-foot lengths of 2x6 cedar. If you bought 8-foot boards, cut two of them in half to get the four 4-foot pieces. Cut four 12-inch lengths of 4x4 cedar post for the interior corner supports. Use a speed square to mark straight cut lines and a circular saw or miter saw to make the cuts. Most home improvement stores will also make cuts for free if you prefer.

Stand a 4x4 corner post inside one corner, flush with the top edge of a long board. Pre-drill two pilot holes through the 2x6 into the post to prevent splitting, then drive two 3-inch deck screws through the board into the post. Attach a short (4-foot) board to the same corner post the same way — pre-drill, then screw. Continue around the rectangle, attaching boards to corner posts until you have a complete 4x8 frame. Check that the frame is square by measuring diagonals — they should be equal (within 1/4 inch).

Stack the second set of 2x6 boards on top of the first layer to bring the bed to 12 inches deep. Offset the seams — if the first layer has the long boards overlapping the short boards at the corners, reverse it on the second layer so the short boards overlap the long ones. This interlocking pattern adds rigidity, similar to how bricks are laid. Pre-drill and screw each board into the corner posts below with two 3-inch screws per joint. For extra strength on the long sides, add a mid-span support by screwing a short piece of 2x4 vertically inside the center of each 8-foot side.

Place the assembled frame in its final position and use a level across the top edges to check that it sits evenly. If the ground slopes, dig down on the high side until the frame is level — this prevents soil and water from shifting to one end. You don't need to remove the grass underneath. Lay cardboard or landscape fabric inside the bed footprint directly over the grass — it will smother the existing vegetation and decompose over a few months. Overlap cardboard pieces by 4-6 inches so weeds can't find gaps.

A 4x8-foot bed that's 12 inches deep requires approximately 1 cubic yard of soil (about 27 cubic feet). Use a mix of 60% topsoil, 30% compost, and 10% coarse vermiculite or perlite for drainage — this is sometimes sold pre-mixed as "raised bed mix." Dump the soil into the bed with a wheelbarrow and spread it evenly with a garden rake. Fill to within 1 inch of the top to leave room for mulch. Water the soil thoroughly after filling — it will settle 1-2 inches over the first week, so top off as needed.