Casing material pH and why it is important.

"pH", is a measure to describe the acidity of a medium.
pH 7 is neutral; higher means alkaline, lower acidic.

Peat is a major constituent of preferred casing mixes. The pH of peat is variable, dependent on the source it came from. Meaning, the pH of peat differs from various sources.
The preferred pH range of a casing mixture is 6.5 to 8. 7.5 is optimal.
Peat is acidic. Consequently, to achieve an optimal pH range of a casing mix, the pH of the casing mixture must be adjusted accordingly (within the range of 6.5 to 8).
The pH of the casing must be within certain limits to support strong mycelial growth. An overly acidic or alkaline casing mixture will depress mycelial growth and supports unwanted competitors.
It is generally easier to make casing materials more alkaline (i.e., increasing the pH) than it is to make them more acid (i.e., reducing the pH).
A movement of 0.5 is easy but, because the pH scale is logarithmic, a movement on the order of, 2.0 points becomes more difficult because there is a factor of 10x between each full point, so pH 5.0 is actually 100 times more acid than pH 7.0.

There are several common types of lime available for use, though care should be exercised with all of the products. Lime is caustic and a skin and eye irritant and can be dangerous if misused. If you choose to use such products, carefully read and follow all manufacturer directions exactly. The major types of lime products include:
Hydrated Lime: fast acting, but not long lasting. It is very effective to produce a fast change in pH level. It is also the "strongest" form of lime generally available, and you must follow all manufacturer precautions, since your skin and eyes can be easily irritated or burned if the product is misused.

Ground Limestone: a naturally occurring type of limestone that has been ground to a fine powder. How quickly it will act to modify pH and how long it will persist depends on how finely it was ground.

Generally, ground limestone is weaker than hydrated lime, needing about 30% more to raise the pH by the same amount. It has the advantage, however, of usually being significantly cheaper than the hydrated lime, and usually works more slowly and lasts much longer.

Mixed Lime: usually sold under a brand name. Most brands contain a variety of particle sizes to provide some immediate benefits, as well as a longer persistence. (this is often referred to as "time released" lime).

pH gradually falls to less than optimal by the end of cropping due to acids secreted by the mushroom mycelium. Consequently, a long lasting buffering agent is preferable.

If you wish to achieve optimal results when adjusting pH, it is highly advisable to use litmus strips (with color chart), or acquire a pH test probe (available at most garden supply stores, under $20) to accurately test, and adjust the pH of your casing mix, prior to application.

Doing all other cultivation steps properly, then applying a casing mixture outside the proper pH range, most often creates poor cropping results.


by SixTango