<b><font color="blue">Carl Bozicek, Amycel UK</b> </font>

Further to the aged casing tome of mine that appears elsewhere, I wanted to comment upon what appears (at least to me) to be currently salient points on casing characteristics.

It goes without saying that a disease free, manageable material that holds copious amounts of water within its structure for the duration of the flush is the nirvana of most casing manufacturers. 

A casing that readily yields its water to the crop is unfortunately one that will not produce high quality mushrooms.  The casing needs to have a high osmotic pressure so that the mushroom have to work hard to replace moisture lost due to evaporation and utilisation as it grows.  This replacement moisture is best obtained from the compost in the form of a nutrient "soup" rather than "fresh water" easily taken from the casing.  I admit that I have no idea if this view is actually technically correct but argue that observations made in the field over the years have more often than not been corroborative.

The above simplistic explanation highlights the dilemma in manufacturing casings soils where the required characteristics have to be balanced against producing a material that can be handled in the mushroom farm. The heavier deep dug peats are ideal at holding water but can be difficult to handle on the bed, so a compromise has to be made.

We are looking for a casing that is not too "open" nor too "solid" and definitely not anaerobic: 

A deep dug material with perhaps a relatively small percentage of milled "brown" material added for manageability mixed together with SBL is one of the most commonly used mixes.  The quality of the deep dug material is a very important factor.  This dense material should contain many small air spaces that hold moisture effectively, and make the moisture harder to extract.  Adversely, this material will be harder to fill will water if over-worked or over-dried. The deep dug material should contain a good supply of string fibre, this will not only provide safety against mechanical over-working but they will also provide "wicks" as routes for water movement through the denser parts of the material.

One can also have a sludgy casing that will hold a lot of water but has air spaces that are relatively large and thus again osmotic pressures will be lower.  Over-working can also reduce the water holding capacity of this type of material as it is easy to knock the c**p out of most casings during application and remove the air spaces completely.  Such a result will be less suitable for use with Ph2 compost because here, water input tends to be applied with the casing behaving as a slow funnel to the compost.  Excess water applied will not be readily absorbed by the casing but instead pass down to the interface and probably cause damage.  High water inputs will consequently be  extremely difficult to achieve.  This will be less critical with Ph3 compost but in both cases total water input will be limited so reducing the availability of water to the crop.

Readers might comment that there is nothing new in the above text.  This is true, but I have recently seen various materials (after application - i.e. not the supplier's responsibility!) that definitely do not match my perceived idea, or those in the accepted tomes on casing, for an ideal casing as described above. These characteristics are important and growers should keep an eye on the “creeping variances” as Geoff Ganney used to say. !

CKB October 2009.