An Interview with Organic Architect Patrick Blanc
There’s no soil involved at all?
Plants don’t need soil in any situation because the soil is merely nothing more than a mechanic support. Only water and the many minerals dissolved in it are essential to plants, together with light and carbon dioxide to conduct photosynthesis. Wherever water is available all year long as in tropical forests or in temperate mountain forests, plants can grow on rocks, tree trunks, and slopes free-of-ground.
For instance in Malaysia, 2 500 out of the 8 000 known species are growing without any soil. Even in temperate climate zones many plants grow on cliffs, cave entrances or cracked up rocks. On these rather steep places many Berberis, Spiraea, and Cotoneaster species are able to grow. Their naturally curved branches indicate that they originated from natural steep biotopes and not from flat areas like the gardens where they are usually planted. So - it is possible for plants to grow on virtually any vertical surface nearly free-of-ground, as long as there is no permanent shortage of water.
interview (and more pictures)