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Limestone Substrates

I thought I might add a word here inspired by my reading of Eduardo
Goncalves’s article in the recent Aroideana. For those who might not
have gotten into the issue that far, the article is entitled “The
Araceae from the Limestone Outcrops in Central-Western Brazil”. As the
title suggests there are aroids that are adapted to limey substrates.
I was surprised that they are as common as he indicates.

Of course, a substrate dominated by limestone (calcium carbonate) will
have an effective pH in the range of around 7.5 to about 8.5. Compared
to the typical horticultural blend, containing generous amounts of
organic material and, perhaps, pH-neutral amendments like vermiculite
and silica sand, limestone-dominated substrates are very distinct
growing media. Organic-dominant soils will have pHs in the range from
about 6.5 to as low as perhaps 5.

Chemically, the pH difference between 6 and 8 is drastic all by
itself. In addition to pH, it’s pretty certain that the nutrient
content and elemental availability of whatever might be present is
also very different between soils at the extremes. Anyone familiar
with soil science will know what I am talking about. I am thinking
that plants adapted to grow in calcareous substrates (those containing
limestone and its variants) will do poorly in the typical planting
media used by domestic growers.

>From time to time we’ve had discussions in this forum about substrate
likes and dislikes. For example, I remember a rather lengthy
discussion a while back of the merits and demerits of using coir. My
query to our readers is whether anyone has attempted to pay attention
to soil pH and/or limestone content in the growing of aroids. It might
be that certain “difficult” aroids are seen as difficult only because
they have been grown in inappropriate soils.

Ted Held.
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