Bougainvillea on Roof Terrace
I have a rooftop terrace in zone 10 with a 40 foot long fence along which I would like to plant bougainvillea that will fill out and climb to form a beautiful occlusive wall. I'd like the height to be around 8 feet ultimately. I want to build a 40 foot long planter with the same wood as the decking along the fence line for this purpose.
Can anyone please tell me how deep and wide I should make this planter? (Or at least the cubic foot of soil volume I should aim for). Also, how far apart should I plant the starts?
Any other recommendations for the planter specific to bougainvillea? I know it needs good drainage. I'd like this planter to last as long as possible.