Step 2: Preparing the wood
The planks will be used to line the frame and make it more solid so it will later hold the weight of the earth back. Saw the planks at the right size to fit the frame. In the end you will get three pieces: a short one for the top of the frame, and two long ones for the sides.
The blocks (approximately 10 x 5 x 5 cm) will be used to attach the frame to the wall. Because you will use the long sides for this, get long nails (around 15 cm). Drill a hole through the wood using a drill with a diameter slightly smaller than the screw, then put the screw through.