Vertical gardening takes very little effort once it has been put in place. Looking after it three or four times a year is usually enough. It creates it's own humidity and can subsist on a weak fertilizer solution added to the drip lines, which provide water in much the same way as the surface of a cliff. Vertical gardens have been shown to improve atmospheric humidity in their vicinity, so are perfect for greenery-starved high density cities.
I first became acquainted with vertical gardening on a visit to Paris, where I saw this lively assortment growing at the Quai Branly Museum. From then on, I've seen them in many other places in my travels and they delight every time!
And this example is um, vertical gardening of another sort?
Patrick Blanc, a french artist who also happens to have a very green thumb, is the man responsible for the renewed interest in vertical gardening. He has constructed his botanical tapestries in dozens of private and public spaces around the world. Many of his creations use over 1.000 plants!
If you would like to try vertical gardening for yourself, check out this month's issue of Lowe's Creative Ideas. In it, they give details instructions for making a 'living wall' with drought tolerant succulents and moss, at a cost of only about $200!