I am wondering about the role of charcoal as an additive to potting media. I
have seen references to charcoal "sweetening" a bark mix, but what does that
mean?

While in Wisconsin, I helped my mother-in-law repot one of her orchids, and
was surprised to find a huge chunk of charcoal in the pot (this orchid had
been potted in sphagnum moss). Since the orchid had been flourishing
especially well and we didn't know if the charcoal chunk contributed to
that, we decided to leave the charcoal chunk in it and just replaced the
moss with fresh bark (since my mother in law prefers bark).

Any insight on the role of charcoal for orchids would be appreciated.

Joanna

If I'm not mistaken, the "sweetening" effect is the absorption of
decomposition byproducts.

However, we have to keep in mind that this is absorption into the
surface porosity of the charcoal granules, NOT adsorption as happens
in activated charcoal. There is _some_ activation in horticultural
charcoal, but it is miniscule compared to truly activated charcoal.
"Activation," in this case, refers to heating to create a great deal
of surface area in the form of microporosity. Some activated carbons
have as mush as 3000 square meters of area per gram, while the
porosity in horticultural grades can be as low as a few square meters.

If you use regularly charcoal in your media, you'll see that it
develops mineral deposits long before other components, and it's
particularly difficult (read as "impossible") to leach them out again.

I used to mix fine charcoal with sphagnum for phals, and it seems to
keep the moss from compacting as rapidly as it did when used alone...

There are other theories concerning "cation exchange capacity," but
that relies, again, more on adsorption than absorption, so the
relatively low activation of horticultural charcoal limits that, as
well.

On the other hand, charcoal absorbs water quite well, then releases it
back into the medium as the overall content diminishes.

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Books, Artwork, and Lots of Free Info!
..
"J Fortuna" wrote in message
news:kXABd.15767$L7.2151@trnddc05...
I am wondering about the role of charcoal as an additive to potting
media. I
have seen references to charcoal "sweetening" a bark mix, but what
does that
mean?

While in Wisconsin, I helped my mother-in-law repot one of her
orchids, and
was surprised to find a huge chunk of charcoal in the pot (this
orchid had
been potted in sphagnum moss). Since the orchid had been flourishing
especially well and we didn't know if the charcoal chunk contributed
to
that, we decided to leave the charcoal chunk in it and just replaced
the
moss with fresh bark (since my mother in law prefers bark).

Any insight on the role of charcoal for orchids would be
appreciated.

Joanna