Tufa Rock
Tufa is a naturally forming limestone rock which can be used as a medium for growing certain plants.
Tufa is formed when lime deposits in a stream build up over the years around debris such as small twigs and leaves. The imprints of the debris is clearly visible in all tufa rock. While the exterior surface of the rock hardens with age, the inside remains soft enough for plant roots to penetrate and extract all the nutrients required to sustain the plant. Being porous, the rock will hold a resevoir of water and take up moisture by capillary action from the soil below. While any lime-loving plants can be grown in tufa (it is often used in bonsai cultivation) the most suitable are those high alpine cushion plants which have low nutrient and low water requierments. These plants will happily live for a number of years with only the occasional top up of water during a hot summer. Even a small piece of rock can have a comparitively
large surface area, so a number of plants can be planted in each piece. In general the planting distance should be no less than 20cm.
Plants suited to tufa cultivation include:
Saxifrage (silver foliage and 'kabschias')
Androsace varieties
Drabas
Some Helichrysums
Dwarf/cushion Dianthus
Vitaliana
Select the positions for your plants - make the holes in the rock approximately 2-3cm wide by 10cm deep. This can be easily achieved with a drill and an old teaspoon. Make sure the holes slope downwards so that any rain or water will flow into the rock. Take the plant out of the pot and carefully roll the roots to make a long sausage shaped root ball which can be persuaded to fit into the hole - if the rootball is too long, simply break off the bottom few centimeters of root.The tufa dust from the planting hole can be mixed with an equal part of soil and used as a filler when planting the alpine. A pencil can be used as a dibber to firm the plant and poke the filler compost around the roots. Once completed the plant should be sitting tightly on the rock. If loose, small pieces of tufa can be used as wedges around the neck of the alpine or a wire staple can be used to temporarily pin the plant to the rock. After planting regular watering will be required until the roots have grown into the rock.