GROWING GOURMET - Anto2ni.it

210 CASING: A TOPSOIL
A dozen or so casing soils have been used
successfully in the commercial cultivation of
mushrooms. They all revolve around a central
set of components: peat moss, vermiculite, calcium
carbonate (chalk), and calcium sulfate
(gypsum). Recently, "water crystals," a watercapturing
plastic, have been tried as a casing
component with varying results.These crystals
can absorb up to 400 times their weight in water
and do not support contaminants, two highly
desirable characteristics.
Unfortunately, the
fact that water crystals are not fully biodegradable
and can not be easily recovered from the
spent substrate greatly limits their acceptance
by environmentally astute growers. Starchbased
water absorb ants tend to clump and must
be added with an aggregate. Cultivators must
weigh in balance these factors when designing
the casing mixture.
For many years, cultivators have used the
following casing formula.
Casing Formula (by volume)
10 units peat moss
unit calcium sulfate (gypsum)
1
I unit calcium carbonate (chalk)
Calcium carbonate is used to offset the acid-
ity of the peat moss and should be adjusted
according to desired pHlevels. Calcium sulfate,
a non-pH affecting salt*, provides looseness
(particle
and mineral salts, especially
sulphur and calcium, essential elements
for mushroom metabolism. Peat moss, although
lacking in nutrition, is resplendent with
mushroom stimulating bacteria and yeasts .The
above-described formula depends greatly on
the starting pH of the peat moss. Generally, the
pH of the resultant mixture is 7.5-8.5 after
make-up. As the mushroom mycelium colonizes
the casing layer, pH gradually falls. For
some acid-loving species mentioned in this
book, calcium carbonate should be excluded.
Typically, this chalk-free mixture gives pH
readings from 5.5-6.5.
Mix the dry components together in a clean
bucket or wheelbarrow. Add water slowly and
evenly. When water can be squeezed out to form
brief rivulets, then proper moisture has probably
been achieved. A 75% moisture content is
ideal and can be tested by measuring the moisture
lost from a sample dried in a hot oven.
Once wetted, the casing is applied to the top
of a substrate, but only after it has been thoroughly
colonized with mycelium. Casing soils
are best used with tray, bag, or outdoor mound
culture. Although some of the following mushroom
species are not absolutely dependent
upon a casing soil, many benefit from it.Those
species marked with an"*" are dependent upon
soil microorganisms for fruitbody formation.
Under sterile conditions, the "k" species will
not fruit well, or at all. Typically, a one-inch
layer of casing soil is aplaced onto 4-10 inches
of myceliated substrate.
Agaricus brunnescens*
Agaricus bitorquis*
Agrocybe aegerita,
Coprinus comatus
Ganodernia lucidurn,
* Gypsum.
The Button Mushroom
The Warm Weather
Button Mushroom
The Black Poplar
Mushroom
The Shaggy Mane
Reishi or Ling Chi
calcium sulfate, may affect pH by 1/2 of a
point. Its pH-altering ability is minor until the
sulphur evolves into sulfuric acid. Calcium and
sulphur are essential elements in mushroom
metabolic processes. If the substrate is lacking in
these essential elements, yields are adversely
affected. Shiitake, in particular. benefits from the
addition of calcium sulfate to sawdust substrates.
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