pH and soil mixes

Barry Meyers-Rice (
Thu, 17 Feb 94 10:27:25 MST

>>So are _Pings_ that are said to grow in a neutral or neutral-basic media
>>really doing so?

>If you take one of those meters on a stick (you know, the portable pH
>metre kind that not so cheap stores like to con us into buying) and if
>you plunge it into the soil where these lime lovers reputedly live,

You know, I once heard that those portable pH meters on the long metal
probes do not measure pH directly, but rather measure something else,
maybe conductivity of water or something which is not the same thing
as pH in some circumstances. Does anyone have comments on this? I measure
pH in the field with my rolls of pH paper, one goes from 1--14, and the
others have more limited ranges. I usually get sensible results this way.

I had a great time this summer at one pond (Terry, the one I wrote about
for the Bulletin of the A.C.P.S.) in South Carolina. I got in a friendly
argument with a relative. I said the pH of this _Sphagnum_ bog was probably
in the range of 4--5, he said it was probably 5.5--7. Since I know something
about bogs, and he works with water quality and sewage, we both respected
each other's knowledge base. So when we worked out an arrangement where I
would borrow one of his nice and fancy pH probes from work (that one of his
chemists calibrated that a.m.) we both got nervous enough that we adjusted
our pH estimates to 4--5.5 and 5--7. Well, I measured the pH in several
places in the bog, including where water entered and exited, and in
beds of _Sphagnum_ (at various depths), and found that the water was all
hanging around 5.1--5.3, right in the overlap region of our two estimates!
Now, that's science for you!

>An obvious test is to supplement the mix with granulated gypsum rather
>than ground limestone. You don't need much because it dissolves faster
>than limestone.

>In the past, I have only used gypsum outdoors to flocculate clay soils.
>Large amounts (10-20 lb/100 square feet) can be applied to correct salt
>pollution without apparent phyto-toxicity.

I know someone who puts a big chunk of ``plaster of paris'' (gypsum) in his
_P.gypsicola_ pots. They do wonderfully.

So, I've been reading the latest bulletin from the Ping Study Group, where
Studnicka recommends the use of ``chalky clay'' as a potting material.
It sounds like he gets the stuff from some ``Cretaceous formation.'' For
those of us not so geologically well placed, is there some good replacement
for this? When I think of clay, I envision the dense gritty stuff I used to
see on riverbanks in the midwest. Sure, it was fun to slide on and make into
little primitive figures, but is this the same stuff Miloslav is talking