How to Make Square Concrete Pots

Measure and cut five 10-inch-square pieces of plywood. Measure and cut five 6-inch-square pieces of plywood. Set the smaller squares aside.

Lay one of the 10-inch pieces flat. Line up each of the other four 10-inch pieces along one side of the flat board, making the ends flush. Drill a screw into the side of the upright piece into the edge of the flat piece 2 inches from each end where they meet. Repeat this step for all four sides to create an open-faced box.

Repeat Step 2 with the smaller squares to create the smaller box.

Lay out and center a plastic sheet over a workbench.

Coat the exterior sides of both boxes with linseed oil. The oil will help the pot slide free of the mold.

Open a bag of ready-mix concrete. Mix the concrete with the proper amount of water as directed on the bag. You want it to be the consistency of thick mud or paste.

Pour concrete mix into the bottom of the larger frame to a depth of 2 inches.

Center the smaller box inside the larger box on top of the concrete mix. Rest the box on the concrete but not in the concrete, as the depth must be maintained to avoid cracking the pot later.

Place a clamp over adjacent sides of the boxes at the center. Set a clamp on each side. Tighten the clamps to keep the smaller box in place.

Pour concrete mix in between the boxes. Push down into the space with a knife, packing the mixture and pushing out any air bubbles. Continue filling the mold until it is full.

Fold the plastic sheet over the molds on all sides. Set a 2-inch by 4-inch board horizontally over the mold to hold the plastic in place. Allow the concrete to cure for up to 14 days.

Remove the board on top of the mold. Unfold the plastic. Flip the mold upside down carefully and gently to avoid cracking or chips. Unscrew the outer box and remove the sides.

Flip the mold right side up again, using care to prevent damage to the concrete pot. Slide the smaller box out of the pot. You may need to wiggle the box free because of how tightly the mold and concrete are fitted together.

Flip the pot upside down. Drill a series of drainage holes through the upturned base. Flip the pot upright to use it.