My greenwall is based on Patrick Blanc's design. Here's a quote from him describing his system published in Dwell Nov 2006:
"10mm thick waterproof PVC slabs covered with polyamid felt, into which holes (pockets actually) are cut for plants; a small hose, punctured every 10cm by a 2mm hole, to run the length of the top of the wall; a timing device to ensure regular, light watering- like a trickle slowly wending its way down a mossy rock. The ensemble is then attached to a metal structure that stands out from a supporting wall, trapping a cushion of air, which acts as insulation."
That's basically exactly what we built. The frame is a lattice work of 1" aluminum ("aluminum square stock" is what you google)tubes. Sheets of expanded PVC (Sintra is the brand name I used) have been screwed on with rust proof screws. Then 2 layers of the moisture retention mat (synthetic felt sourced from Green Roof Solutions product number MRM14) is stapled on with rust proof (Arrow Brand "Monel") staples. There is a submersible pump on a timer that pumps water up to a tube running under the felt across the top of the wall. There is a basin at the bottom of the wall also built from expanded 3/4" PVC.
We planted 3.5 inch plants in slits 5" wide separated horizontally by 2" gaps. The rows were 4" apart vertically and the plants are staggered every other row.
