Download A quick google search will define Tufa as “a highly porous

Tufa:
A quick google search will define Tufa as “a highly
porous, sedimentary rock (limestone) composed
of calcium carbonate, CaCO3. It is formed by
biological and chemical precipitation of Calcite or
aragonite from cold, supersaturated surface or
ground waters (springs).”
You may be wondering “Why are you writing
about a porous rock for this month’s tips?” Well,
quite simply, tufa is the talk of the town right now
in rock gardens and will soon be the featured rock
of the new alpine house at Betty Ford Alpine
Gardens. In fact, tufa is already being used in the
rock garden. So, what is so special about tufa for
alpine and rock garden plants? The first thing to
know is that tufa is very porous, almost like a
sponge, which can mean a few things. 1. It drains
freely 2. It allows roots to grow in and around the
rock. If you have ever seen alpine plants in their
natural habitat in the mountains, you’ve probably
seen them growing in and among rocks. This
adaptation is quite hard for gardeners to duplicate
on any old rock which is where tufa comes in. This
delicate rock is quite light in comparison to other
denser rocks of comparable size. This makes it
Tufa Garden near Woodland Walkway
Tufa cliff in an alpine house in Europe – Photo: Mike Kintgen
easy to place and work with. Tufa is typically
placed partially buried to 1/3 to ½ by soil or other
growing media such as sand or peat. This technique allows the rock to absorb water and the
plants to grow into the soil. Tufa can contain small to large holes that allow plants to be directly
transplanted into it. If there are none, holes are also created by using a mason bit and drill. The
plant is then carefully placed into the hole where
it will then grow into the rock. Tufa can also be an
excellent medium for plants to re-sow themselves
in. Smaller tufa is often used in troughs or
sometimes used as a small display piece in itself.
This is for serious plant collectors and growers
who want to try more difficult alpines.
The tufa that the gardens will be selecting is
coming from a reputable source in South Dakota.
Several tons of this stone will be shipped in the
spring where it will be placed inside the alpine
house. It will be arranged naturally with much thought and care for design. The
Tufa boulder in SD
design of the bed will look “natural” like a mountain scene, and have several micro
growing conditions for unusual plants such as cliffs, overhangs and shady crevices. This will
provide habitat for some new, rare and difficult to grow plants.
In next month’s issue I will discuss some of the plants that grow in tufa and more on the alpine
house.
Large tufa rock in Mike Kintgen's high elevation garden