What different casing layer ingredients are there?
Peat (=Sphagnum Peat Moss)
Unconsolidated soil material consisting largely of undecomposed, or only
slightly decomposed, organic matter accumulated under conditions of excessive
moisture. Main ingredient of many casing formulations, its pH ranges from 3-4
(acidic), has to be brought to neutral or slightly basic (pH 7-8) by adding
a buffer (limestone flour, calcium carbonate or oyster shells)
There are different kinds of peat, depending on its decomposition
state. In mushroom cultivation mostly the darker varieties are used.
Vermiculite
Ingredient of the popular 50/50
casing mix, can also be used as the solely casing ingredient. The drawback of
using pure vermiculite is that it's hard to tell the moisture of the casing
by solely looking at it's surface, since the vermiculite stays more or less
the same color despite its saturation level. Other materials, like peat or coco
coir have a lighter color when they dry out.
Peat based potting soil
Can be used instead of peat, in this case one can use less limestone flour,
since the pH of the soil is usually already around 5 - 6.
Coco coir
It has very good water retaining capabilities and can be used as a casing material
either alone or in mix with peat and/or vermiculite.
Used in the 60/40 Vermiculite
and Coco Coir Casing Tek.
 On the left is expanded coco coir. On the right is coco fiber, which is NOT what you want! |
 Coco coir usually comes in compressed bricks each weighing a bit more than a pound. When water is added, it expends to a tenfold volume. |
Limestone flour (Calcium carbonate, CaCO3, chalk (NOT blackboard
chalk!)
Acts as a buffer agent in the casing formulation, rises the pH. Depending on
the initial pH of the casing mix, 10 -20 vol% of limestone flour should be used.
Limestone is the buffer agent used by the most cultivators. Also used as feed
supplement for cows and horses.
http://www.google.com/search?q=limestone flour
Hydrated lime, Ca(OH)2
Also rises the pH but it's a much stronger base than limestone, therefore it
should be used only in about 2/3rd of the amount compared to limestone.
Generally limestone is preferred to hydrated lime. If you use hydrated lime
make sure to measure the pH of your casing or you might end up with a much too
high pH, the reason for many failures.
ATTENTION: Hydrated lime can cause irritation of the skin, even blindness,
if it's in prolonged contact with eyes, so be careful when handling it.
Crushed oyster shell
Chemicaly mainly CaCO3, but its structure is much coarser than limestone
flour therefore the immediate effect on the pH is not so strong. But it acts
as a longtime buffer along with limestone, so it's a good idea to substitute
a part of limestone with crushed oyster shells.
Check this FAQ for sources for some of the the above ingredients.