I have a 28' wide structurally-sound rooftop terrace that is looking pretty bare, garden-wise. The terrace overlooks a major street in central Toronto. There is a newish 5' tall black chain-link fence running the entire 28' width that sits on top of a 3' brick "knee" wall, probably erected to keep people from falling off the roof onto the sidewalk below.
Several friends have suggested I erect a cedar hedge against the 5' fence, growing from a to-be-contructed trough-like P.T. container that would be permanently attached to the steel flashing that covers the top of the 3' brick wall.
The only problem is that I have only 12" of width for the "trough" to sit on, and would like to restrict the depth of this to 12-15" maximum.
My question is this. Is there enough soil mass in a 28 foot-long 10" wide x 12" deep container to support 9 or 10 cedar shrubs placed 30" apart?
How durable would such a container be, assuming I used pressure-treated (P.T.) wood? Would 1/2" diameter holes drilled near the bottom provide adequate drainage?
Thanks for any advice any of you may have.