Create sturdy concrete containers for your patio, yard or garden to spice up a spot and give it a rustic appearance. Concrete has a natural appearance that blends with the surrounding and lasts for many years. Depending on your taste and available space, make square or rectangular containers and plant a single large plant or several smaller ones, or any angular shape for added appeal. Avoid making the concrete containers thicker than 2 or 3 inches, as they could get heavy and difficult to move when filled with soil.
Determine the length, width and height of your container so you can cut the ¾-inch plywood to make two molds accordingly. Each mold requires five lengths of plywood for its five sides--two long sides (for the front and back), two short sides and a base. The inner mold should be 2 inches smaller than the outer mold, so the concrete you pour between them cures to form a 2-inch-thick container.
Measure and draw lines for the five sides of inner mold on the plywood. Cut over the marks with a handsaw. Repeat the process for the outer mold. Sand all edges with a medium-grit sandpaper to make them smooth.
Assemble the inner mold by attaching the long and short edges to each other with nails to form a square or rectangle. Use two wood screws per short side and three for the long sides. Turn the structure upside down and attach the base. Assemble the outer mold the same way.
Lower the smaller (inner) mold in the bigger (outer) mold. Drill a 1-inch-wide hole through the middle of both bases. Lift the inner mold and lubricate it by spraying oil on its outer walls. Spray cooking oil on the inner walls of the outer mold.
Mix concrete to water according to label directions. Insert the plastic pipe in the drainage hole of the outer mold. Add concrete over the base, and level it with a hand trowel.
Lower the inner mold inside the outer mold, extending the pipe through the drainage hole in its base. Add concrete between both the molds until it is an inch below the rims. Level the concrete with a hand trowel, pressing it down gently to remove trapped air pockets.
Allow the concrete to cure for 24 hours. Gently remove the inner mold, which should slide off easily because of the cooking oil. Turn the container over and remove the outer mold. Allow the container to dry for at least three days before adding soil and planting.