Here's a figure deep in thought on a plaza in the museum district of Madrid, Spain. It's a beautiful spring day. What could he possibly be so perplexed about?
Nearby, there's a garden with many kinds of flowers, some of which look suspiciously like foamflowers native to the U.S.
Some others look like hostas and wild geraniums. Nothing particularly unusual.
But wait a minute! They're growing on a wall! Now that IS something to puzzle over.
From the side of the wall, it looks like the plants are growing in nothing much more than a thin wool-like fabric with small pockets cut into it, and a strong nylon backing. One thing about wall gardens: They're easy to water. Water is released from the top of the wall and trickles down through all the vegetation below. And you get a big effect while using next to no real estate.