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Trying to assess poor David Kurtz' root
problem from the information provided is a little like Senator Frist trying to
assess Terry Schiavo's brain activity from film clips. To begin with the
problem with pH is not that it is difficult to measure but it is so ephemeral
when measured in pure, unbuffered water. The slightest thing can alter the
pH, usually downward, as Leo pointed out, even the environment of the
medium around the roots. As Tris comes out of the bottle it is
strongly alkaline and would further raise the pH. I don't see why anyone
would advise sodium citrate, which is also alkaline, but I don't understand
what could be meant by Oliver's comment, "...not very durable in
solution".
I do not understand why so many growers get
hung up over pH, but the easiest way of lowering pH into the truly neutral zone
would be the addition of almost any commercial fertilizers; all I have tested
are distinctly acidic. I concur with Leo's comment about using fertilizer
to adjust pH. If pH control is the objective, addition of as little of 1/4 tsp
would probably do the trick. The fertilizer I advocate, Jacks [used to be
called "Peters"] Classic Excel Cal-Mag, [15-5-15], is mildly acidic and low
phosphate to boot. It resembles the MSU formulation and is easier to find.
I am not convinced that high phosphate contributes to the problem, but no one
has documented that it ever does any good, despite all the advocates of high
phosphate "blossom booster".
Regarding hardness, remember plants do not
have built in conductivity meters and the nature of the salts present in the
water is all important. I suspect even moderate amounts of Sodium are bad,
but orchids have a rather high requirement for Calcium. The municipal
water in Miami has its Calcium content LOWERED for laundry purposes by
the ADDITION of CALCIUM HYDROXIDE, which paradoxically lowers Calcium from
about 100 ppm to 40 ppm by raising the pH to about
8.6, thereby allowing some of the Calcium originally present to
precipitate as Calcium Carbonate. Nevertheless most of
the commercial orchid growers in the Miami area use untreated well water
successfully. Incidentally our water is practically devoid of the major
nutrient, Magnesium, hence the added beneficial effects of
"Cal-Mag".
It may be that orchids from cool high
elevations are more sensitive to moderate salt concentrations, even
Calcium, but they are not grown in our
area. Bert
Pressman
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