Tufa bed

In the immediate vicinity of the large fissure bed, a bed of tons of tuff, a very porous limestone material, has been established. The tuff is formed continuously in rich-lake environments, where calcium-saturated water comes into contact with open air, causing carbon dioxide to evaporate and the lime to precipitate as calcium carbonate – i.e. limestone.

Bacteria, blue-green algae, mosses, leaves and twigs are encapsulated in the limestones, making them extremely porous and suitable for planting alpine plants.

The formation of the tufa stones used is a very slow process, and based on the fossils found in the stones, they are believed to be about 60 million years old. The stones come from a quarry near Munich, and are sponsored by the Circle of Friends.

The stones are placed in a "vat" of sand with underlying rubber foil, so that the stones can absorb moisture all the way to the top of the material, and thus provide moisture to the plants that are placed in the stones.

The planting is special in that holes are drilled for the plants in suitable places in the tuff blocks. A 15 mm masonry drill and a hammer drill have been used to make holes - preferably sloping backwards downwards and as deep as the drill can reach. The drilled lime material is collected and has been very carefully stuffed between the roots in the planting holes with thin wooden sticks.

The lime material can be mixed with a little growing medium and sand, and a small lump of clay can be placed on the outside to hold the plant in place while it establishes itself.
Experience shows that the many plants planted in cracks and crevices in sand and tuff soil have been able to establish themselves very quickly, while the plants that have been very carefully placed in drilled holes need a little longer to recover and form new rosettes.