What you will need
1x1 pine edging
Spade drill bit (32mm)
Sander (any kind)
How to do this project
Cut your pine sleeper to desired length, it all depends how big you want it and the quantity of plants.
Mark out a rectangle on the sleeper, this is where the plants will go. Again it all depends on how big you want it.
Get the drill with the spade bit and just randomly drill out inside the rectangle at desired depth, go as close to the line as possible. The edging will cover up any mistakes doing this.
Then when most of its out, use a sharp chisel to chisel out along the edges and tidy it all up. Like in the picture. Drill drainage holes going through the material.
Sand the sleeper and line the inside of it. Paint and glue the edging along the edges like in the picture. Then add the soil and your plants.