Garden containers include planters and pots made from wood, ceramic, bricks, concrete, metal and a variety of weather-resistant materials. These containers allow people who lack garden space or own poor quality soil to grow plants, vegetables, flowers or herbs of their choice year round, both inside and outside. Although planters or pots made from any of the materials above offer their own set of advantages, rectangular concrete planters are very easy to construct, are sturdy, add rustic charm, and are disease and rot resistant.
Mark the plywood to create the pieces needed to create two rectangular molds. Each mold should resemble a rectangular box with five sides--a front and back, a base and two sides. Keep the outer mold 2 inches larger than the inner mold overall, so your container is 2 inches thick. Visualize the final length, depth and width of the concrete planter to decide each form's dimensions.
Cut the pieces for each mold with a handsaw.
Assemble each mold, in turn. Secure the front piece of the mold to a short side with wood glue. Then glue the back to the structure before attaching the second side. Flip the structure over and place the base over the cavity.
Drill a 1-inch wide drainage hole through the bases of both the inner and outer mold, in turn. Make sure the locations match. Lift the inner mold and spray an even coat of cooking oil on its outer surfaces to lubricate it. Also spray cooking oil on the inside of the larger mold.
Mix cement and water until the consistency of ice cream. Place the plastic pipe into the hole in the base of the outer mold to prevent it from blocking with concrete. Pour 2 inches of concrete into this mold and shake it gently to level the top.
Place the smaller mold inside the outer mold. Extend the drainage pipe so it leads out of the hole in the inner mold. Pour concrete slowly between both molds until it reaches an inch or two below the rim.
Press the inner mold down a little to remove trapped air bubbles. Let the concrete cure for 24 hours. Grasp the outer mold and pull it gently to release it. Remove the inner smaller mold. Both molds should come off easily because of the lubrication.