Fargesia in wooden planter

Igrowfromseed

I'm planning on making a wooden planter similar to the picture. 2m long by 50cm high and 30cm deep. It's for a fargesia to be used as a screen. Should I line the planter with plastic to retain moisture.  I know fargesias like moist but free draining soil; how best can this be achieved in this planter? The planter will be sited on some wooden decking
Thanks