Cut four landscape timbers into 16 2-foot-long sections. Each 4-inch-square timber measures 8 feet long; one timber will yield four 2-foot sections.
Stack two 2-foot-long timbers lengthwise so that the edges are flush. Hammer a 6-inch pole barn nail through the top timber and into the bottom timber 2 inches from each end.
Stack a third 2-foot-long landscape timber on top of the second timber. Make sure that the edges are flush. Insert 6-inch-long nails through the third timber and into the second timber, 4 inches from each end.
Stack a fourth 2-foot-long landscape timber on top of the third timber; fit the timber so that the ends are flush. Hammer a 6-inch pole barn nail through the fourth timber and into the third timber, 2 inches from each end. The four 2-foot-long landscape timbers make up one side of the flower pot.
Repeat Steps, 2, 3 and 4 three more times to make the remaining three sides of the flower pot.
Stand one completed side of the flower pot at a 90-degree angle to a second completed side. Fit the outside edges of one side flush against the outside edges of the second side. Insert a 6-inch-long pole barn nail through each of the four landscape timbers to join the two sides together.
Repeat Step 6 to join the two remaining sides together. Fit the two sections of the flower pot together to make a square. Insert 6-inch pole barn nails through each timber to join the seams together.
Measure the length and width dimensions from the outside edges of the flower pot. Measure and cut 1/2-inch-thick treated plywood to fit. This is the base of the flower pot. Attach the plywood to enclose one of the square openings created by the four timbers sides. Insert 2-inch-long deck nails every 4 inches around the perimeter of the flower pot.
Drill four 1/4-inch-diameter drainage holes through the plywood. Space the holes 3 inches apart.