Diatomaceous earth is composed of the silica skeletons of diatoms. For
those unfamiliar with the product, it can be found naturally as clay-like
or rock-like forms. The clay-like form is finely powdered and is used
both as a polishing agent and as a filter medium.
The rock-like form is crushed and sold both as kitty litter and as an oil
absorbent for garage use. One common name is oil-dri.
Diatomaceous earth has lots of surface area, like zeolite clays. It is
therefore great for adsorbing other materials, buffering variations in
nutrients and PH. When mined, it has rather a lot of trace mineral ions
already adsorbed so it is often used as a trace mineral amendment.
It holds water well but also passes air freely. It shares that
characteristic with the open-pore forms of agricultural pumice.
I use it in place of pearlite. It is at least as good for encouraging
drainage but doesn't float out the way pearlite does. Some hydroponic
growers use it exclusively. The oil-dri/kitty litter packaging is most
availabe but must be sifted to remove the largest and smallest particles.
It is a great equalizer. A recent edition of the CSSA journal reported
cacti and tender herbs growing close together in a high rainfall area
rooted only in diatomaceous earth. The drainage and porosity kept the
cactus roots from rotting while the water holding ability kept the herbs
from drying. The mineral holding ability prevented all nutrients from
being washed away. Neat stuff!
Bob Cruder - bcruder@miaco.com