Adding lime or soda ash to raise the pH
Soda ash – commercially manufactured anhydrous sodium carbonate.
How much to add these components depends on:
- alkalinity/acidity of your water;
- method of processing raw materials;
- the quality of the lime itself.
The main goal is to bring the pH (ph) of the substrate to 7.8-8.5.
Speaking in a completely scientific way, pH does not show the alkalinity or acidity of the substrate (or water) separately, but the acid-base balance.
If it is 7, the solution is said to be neutral.
If more than seven, then it is alkaline.
In some regions, the water has an alkaline reaction (above 7), and the substrate overgrows without stains and mold. If the mushroom grower uses fresh, clean husks, lime can be omitted.
Alkalize the water for the oyster mushroom substrate if tap or well water has an acidic reaction – from 6.5 and below.
How does pH affect the growth of oyster mushrooms
For the qualitative growth of oyster mushroom mycelium without spots, certain values of the alkalinity of the plant mass are needed.
After heat treatment, it should be in the range of 7.5 (preferably 7.8) – 8.5 (8.2).
It is with this value that the oyster mushroom mycelium develops well. And the straw or husk is gradually acidified by the waste products of the mycelium.
Mold grows well in more acidic environments, so the pH we need will inhibit its growth.
High alkalinity (pH above 9) can damage the oyster mushroom mycelium.
Oyster mushroom mycelium develops slowly in such an alkaline environment; when it is oppressed, colonies of bacteria will grow. As a result, we get yellow spots not overgrown with mycelium.
More about mushroom block overgrowth problems
How much lime to add to the substrate?
You must determine empirically: first give the water for analysis, in some regions it is alkaline enough to not add lime at all during hydrothermia.
But, if you still have to work with lime in hydrothermy, it is preferable to add lime paste to dry husks when filling bags.
When pasteurizing the substrate in the tunnel, a solution of lime or soda ash is poured in equal portions when soaking straw or sunflower husks.
At xerothermy (steaming dry raw materials with steam), lime must be mixed into water, which is used to cool the plant mass.
You can start adding 200 grams of quicklime per 100 kg of soaked raw material or (approximately) 35-40 kg of dry raw material. And be sure to control the pH. If it is lower than necessary, add the amount of lime, for example, take 300 grams.
Which lime is better to alkalize the oyster mushroom substrate
Quicklime (such as in the photo at the top of the article) must be of good quality so that after diluting it in water, all the pebbles will dissolve. Such lime is called fatty (at least, that’s what it is called in my country) – it does not contain insoluble impurities.
In addition, lime must necessarily be calcium, and not magnesian or dolomite. The last two have a large amount of magnesium oxide, MgO, and we do not need this at all.
Ash for oyster mushroom
It will not work to increase the alkalinity with ash. You can verify this empirically – by soaking ash with husks in water, and then measuring the pH.
How to measure the pH of a substrate?
This device is called a pH meter.
It is necessary to make an extract from the substrate in accordance with GOST 26180-84.
Here is a short guide.
Take a glass jar, pour 250 ml of water into it and make a mark at this level.
Here in such a jar with a label, you can now measure the pH correctly.
Take a sample of 25 gr. and fill up to the mark with distilled water.
Stir, leave for 30-40 minutes. Then define.
It is desirable to grind a straw substrate sample with scissors up to 1-2 cm. But, as far as I know, no one grinds it.
When pasteurizing in a tunnel, pH is measured twice – before laying in the tunnel and during sowing, three or four samples (depending on the length of the tunnel) from different places in the tunnel.
This method is, of course, very approximate.
A strip of litmus is pressed with a finger to the steamed mass on the inoculation table and the result will be seen. But there will be no tenths, and sometimes it is important.
Of course, if a litmus paper shows a pH of less than 7, you will understand that you need to add lime, but it will be difficult to “guess” how much to add without an accurate device.