Patrick Blanc is a contemporary garden designer from France who basically “invented” the concept of a vertical garden. What Patrick did is invent a hydroponic structure on which plants can easily grow vertically without any soil. Essentially plants need water and minerals dissolved in it. Many plants in the wild grow on vertical surfaces - rocks and cliffs. Many plants have the root ability to grow without any soil as long as there is sunlight, minerals and water. Being soil-less, vertical gardens are very light and thus easy to implement on any wall. Metal frame is installed that supports two layers of polyamide felt . These layers mimic cliff-growing mosses and support the roots of many plants. A network of pipes provides a nutrient solution containing dissolved minerals. The roots of the plants take up the nutrients they need, and excess water is collected at the bottom of the wall by a gutter before being re-injected into the network of pipes.
(via Design Squish Blog: VERTICAL GARDEN RENAISSANCE