Cut the Boards
Using out cut list above and a miter saw or circular saw, cut the 2×6 boards to size.
Prep the Boards
Using a drill/driver and a pocket hole jig, drill two pocket holes into one edge of 4 of the 5 boards of each wall.
Assemble the Boards
Apply glue to the adjoining edges of the boards. Center the boards. Using a drill/driver and 2-inch pocket hole screws, assemble the boards to create four walls, each made of 5 boards.
Mark the Cut Lines
Mark the width of the bottom of each wall centered on the width of the bottom board. You can keep all four sides the same size (which will result in a rectangular planter) or cut the side walls—that will set between the front and the back—skinnier. I marked the base of my front and back walls at 9 inches, while the sides that will set between them only measure 7 inches. Mark a line from the top corner of each side to the mark along the bottom edge. (or two inches in at the top if you’re opting for skinner side walls like mine).
Trim the Edges
Using a circular saw, cut along the cut lines on each wall. I’m using a Kreg AccuCut to create a straight cut, but you can also clamp a scrap board to the wall to create a fence for the circular saw to ride along.
Assemble the Walls
Apply glue to the edges of the side walls. Stand the sides on edge. Apply glue to the edge of each side wall. Place the front onto the side walls. Drill three pilot holes, and then sink 2 ½-inch screws through front wall and into the edges of the side walls. Repeat to attach the back wall.
Add the Blocking
Using the leftovers from the original boards, or scrap wood, create a ledge for the plant to set on near the top of the planter. Also, if you’re worried about the planter tipping, you can opt to add a base to the planter so it can be filled with rocks or sand to add weight.
Add the Coating
Apply a coating of flexible spackling to the surface of the planter using a large putty/taping knife.
Comb the Coating
Pull a notched trowel of any kind (I’m substituting a Cove Base Adhesive Spreader) across the surface to create the ribbed look. Wipe the trowel off between passes and dip it in water. Start at one edge corners and carrying the pass across the entire wall in one pass. Tip: try tilting the comb handle closer to the surface as you pull for a less raised surface, and at a 90-degree angle from the surface for a deeper groove. Allow the coating to completely dry.
Paint the Coating
Apply several light coats of spray paint to the surface, frequently changing angle and direction to coat all edges of each groove. I’m using a flexible coating meant for plastic that expands and contracts to (hopefully) eliminate cracks in the coating as the wood and spackling expands and contracts.