Figure out where you want to punch holes so it evenly divided the planter into thirds. If your hole is too small, make a few more punches till it is the correct.
Take a cord and string it through and tie a knot.
Then cut the cord to the height that you want your plant to hang (leave a little extra so you can tie a knot at the top. Repeat on all sides.
Then take all 3 strands tie together so you have a loop at the top for hanging.
Take a lighter and singe the ends of the cord strands so they are clean.