How to Plant in Tufa Rock
Tufa is formed as lime rich water evaporates, leaving behind a soft and porous calcium carbonate rich rock. This makes it an ideal rock for use in growing lime loving plants. In addition to its unique mineral content, the porous nature of tufa results in several properties of interest to rock gardeners. Tufa is light and easy to handle. For example, dry tufa can weigh half as much as a comparable size of granite. It also absorbs and holds water. When plants are grown in close proximity to tufa, they benefit from the slow and steady release of moisture. Finally, tufa is easily drilled to form planting holes and plants can be inserted directly into the rock to grow on as true rock plants.
Tools used to Drill Tufa
We use a cordless drill and masonry drill bits to drill directly into the tufa. For planting larger plants with an established rootball, we use a 1" bit while the 3/8" bit is used for smaller rooted cuttings
Drilling the planting hole
A ghost must be drilling this hole (or a driller/photographer). The technique used is to apply light, even pressure and pull the drill bit out of the rock every so often to clear the tufa sand that clogs the drill and slows the drilling process. These bits of calcium rich tufa sand can be saved to incorporate into potting mixes or used in the planting hole. It is not necessary to use a water when drilling this soft rock although the tufa seems somewhat easier to drill when it is moist rather than completely dry.
The planting hole
This planting hole is 1" in diameter and approximately 4" deep. This size allows a fairly large bare rooted plant along with some planting medium/tufa sand to be inserted. When using the smaller 3/8" drill, we generally drill a shallower 2" deep hole.
Planting in the hole
Our planting mix includes a small amount of time release fertilizer to help the plant become established in its new home. Many calcium loving rock plants will grow happily once their roots have tapped into the mineral rich environment of the tufa. If an established plant shows nutrient deficiencies such as yellowing foliage or failure to thrive, it can be sprayed occasionally using a liquid fertilizer.
A bamboo BBQ skewer was helpful to use when inserting this Primula auricula hybrid. The skewer was used to guide the rootball to the bottom of the hole. A flat head screwdriver can also be used for this purpose. After the plant is in place, I used my fingertips to compress the soil in the hole and to remove air voids and then gently pressed small pieces of grit into the area around the crown of the plant. Care must be taken not to damage the plant but this step helps retain loose soil in the planting hole and also provides the usual benefits of a grit mulch to the plant.
Some pieces of tufa have natural planting basins and these can be used as planters. Within a few weeks of planting, the roots of this mature Saxifraga x burnatii plant had penetrated the surrounding tufa and was sending out rosettes to fill adjacent voids. Tufa can also be shaped with cold chisels and planting holes can be created.
Pieces of tufa can be used as stand alone planted rocks. We planted this rock with an assortment of alpine Primulas and placed the rock in a saucer filled with tufa grit.
Is there any sight that makes a rock gardener happier than a healthy flowering alpine growing directly out of rock?
Saxifraga crustata in tufa. Silver saxifrages and dwarf cushion Kabschia saxifrages are ideally suited for growing in and around tufa
Time and Tufa
Here is Kabschia saxifrage 'Simplicity' flowering happily in tufa in mid-winter. Over time tufa will take on the "patina" of age with mosses and, in our NW climate, liverworts becoming embedded in its surface. This is not a problem until it threatens to overrun a precious alpine in which case a spritz of vinegar from a spray bottle can be used to control it.