silica sand- CAUTION

Sat, 15 Nov 2014 17:10:30 PST
Silica sand comes in a number of grades from sugar-like (#30) to chicken
grit-like (#12). It is usually used for sandblasting and is regulated by
OSHA as a hazardous material because of the fine dust that can cause
silicosis in the lungs. I believe the signal word is WARNING. (Perlite, by
contrast, has what is officially regarded as a nuisance dust). Any silica
sand user must abate the risk with rated respirators and follow all
precautions given before use.

Years ago, when I saw a very good collection of species Hippeastrum growing
in mostly silica sand and coarse black lava rock, I decided to try it for
bulbs more sensitive to rotting. My impression after a few years was that
it did yield better results than the general purpose river sand that is
commonly sold for concrete work. Silica sand is almost entirely free of
silt and clay and the sharply angular grains seem to be favored by bulb
roots that attach to them. I would mix this sand, usually #20, with pumice
and less than 15% organic matter. I still like its performance very much
but eventually the health risk outweighed horticultural benefits.

Subsequently I did a little looking into what types of silica sand there
are, looking for an angle because resuming the use of river sand was
somewhat disappointing. From recollection, there are about a dozen
recognized types of crystalline silica sand and a few types of amorphous
(non-crystalline) silica sand. It is the former that poses the danger,
while amorphous sand is not a health risk. This is due to the microscopic
structure of the particles (invisible to the naked eye) that are sharp and
abrasive in the crystalline types of silica sand. Translating this
information into product sourcing is still a work in progress.

Currently I am happy with a "play sand" that is similar to silica sand in
appearance. It is nearly colorless and very clean, with a grade a little
coarser than table salt.

Dylan Hannon

*"The greatest service which can be rendered any country is to add an
useful plant to its culture..." --**Thomas Jefferson*

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