We are using a porous mix which is composed of fine soil (like the one commercialized for seedlings – mostly fine leaf mould) to which a sandy garden soil and a completely mineral mix for the drainage (lava, pumice, granite, washed sand) is added. The mineral proportion varies from 1/3 to 2/3, depending on the species grown. We also add a little amount of charcoal. The size of the draining elements is chosen according to the size of the containers (coarse for big containers, and fine for small containers or seedlings). What is important is that the used mix is not compact when pressing it in the hand (when the mix is lose, it will not retain water for a too long period). In case we use deep containers, we add a little coarse lava at the bottom to ensure the drainage. Finally, a fine layer of coarse sand is put on the surface of the soil, to stabilise the plants and for aesthetic reasons.