A great document by ShroomGod discusses the various aspects of casing.
Hello fellow mushroom growers! Over the last week, I've been considering how
important casing colonization is in mushroom production, especially growing our
favorite friend, Mr. cubensis, the magic mushroom. I've discovered that a casing
really makes or breaks a tray regardless of the supporting substrate. I know of
four common results of casings. Let's go from worst to best.
In the first case, a casing will not colonize at all. Perhaps moisture
content is incorrect or the mix may be too acidic because the cultivator
did not add enough lime flour (peat moss is very acidic by nature). Another
common reason, is packing down of the casing either deliberately or accidentally
through repeated watering; rather, the casing should be sprinkled down and
remain light and fluffy. Yet another reason is that the temperature might
not be in the incubation range (approximately 85oF). In each case, the cultivator
will wait and wait yet the mycelium never makes it through. Given enough
time, mold usually appears. The cultivator might be inclined to think he/she
needs to sterilize the casing next time or try a different casing mix, but
in reality, incorrect conditions set the stage for contamination, not materials.
In the second case, the cultivator will lay the casing but immediately
pins will form before the casing is colonized. In this case, the cultivator
might be very happy to get pins but will soon realize that the first flush
is not particularly impressive. Those mushrooms that do form may even be
large, but they will be few. Soon after the first flush, the uncolonized
casing has a great risk of contamination.
The reason for premature pinning is usually the cultivator inadvertently
presented initiators. Perhaps the casing or substrate incubation temperature
dropped too low (for example, in the mid-70s or even lower). Maybe too much
air or light was given to the substrate prior to casing provoking pins.
For whatever reason, the mycelium switched to the fruiting mode prior to
full colonization of the casing resulting in a meager fruiting and a precarious
position for the casing.
The third case is nearly the opposite of the second. In this case, the
mycelium grows densely through and OVER the casing, and, hence, this is
called overlay. The casing effectively becomes part of the substrate mass
and so looses its ability to store moisture or form pins within its moist
microclimate. The mycelium will often grab the casing so tightly it will
pull away from the sides of the container. The cultivator may try to mist
the casing thinking this will help yet, in extreme overlay, even water cannot
penetrate the casing!
When overlay strikes, the cultivator will sometimes get a decent first
flush but struggles to keep the humidity high enough so the surface doesn't
dry out. Other times the cultivator will see pins only form along the edges
because that's where the moisture is highest. But the worst is still to
come: subsequent flushes will not be any more impressive that without a
casing at all!
The reason for overlay is usually too long of incubation time. I've also
read that too wet of a casing mix can contribute to this condition. It's
best prevented by switching to the fruiting temperatures immediately once
the valleys of the casing show mycelium. Overlay, while very destructive
if not treated, can be remedied by mixing up the casing material with a
fork and waiting a couple days until it recovers prior to fruiting.
The fourth case is what we all want to happen each time. It's casing perfection.
Casing perfection is when the cultivator lays the casing with the correct
pH, moisture, consistency, and incubation temperature. In a week or two,
the mycelium can be seen running through the casing in many of the valleys
but not covering the casing as in overlay. Once the valleys show growth,
the tray is uncovered, placed in the fruiting chamber, and in about a week
(or even less) there are dozens of pins every square inch! The mushrooms
explode everywhere, yet, throughout, the casing remains open and receptive
Why is a great casing so important? In a word, YIELD! Straw trays can fruit
up to 180 dry grams per square foot given a great casing, yet the same tray
without a good casing will produce 20 dry grams per square foot or even less!