An appropriate title for a blog written on Easter Monday.

Normally the 7th day is a day of rest. Good for people after a week of working but not always good if mushrooms take a rest. Read: they stop growing. This can happen during the fructification and if the reaction of the grower is too slow, the flush grows out to be too small.

Fructification is split into two sections. 4 to 5 days for making the mushrooms or forming the primordia. The second part is roughly from day 5 till the start of the first flush. During the first part RH, ambient temperature and CO2 are the main parameters to control the number of primordia. Compost temperature is for me not that important at that time. After day 5 the RH is lowered to let the primordia grow out to be mushrooms. The CO2 is dropped slowly and we also start dropping the temperature to reach 17.5° C ambient temperature at the start of the flush (my favourite temperature to work with).

On day 7 one can see mushrooms developing in the size of 2 to 5 millimetres. And then this phenomenon can occur. You look during your morning check and everything looks good. The next day, nothing has happened. General reaction is waiting. But if you look carefully, in most of the cases the room is not taking enough fresh air. CO2 is okay, RH is okay, air temperature is okay and the compost temperature is declining. If the minimum fresh air setting is too low, the room can have a lack of oxygen and mushrooms just stop developing. Simplest thing to do is to drop the CO2 setting to 800 ppm for a couple of hours. To avoid this however and the best way to handle this, is to make sure that the minimum fresh air setting is around 25%. Then the climate unit will always use enough fresh air and mushrooms keep growing. By the way, this happens mostly with strains which tend to give bigger mushrooms. Because they already tend to give fewer mushrooms.

In many systems steam is used for humidifying the grow rooms. It’s a good solution to keep the right climate in the grow rooms but just keep the amount of steam going into the grow room under control. Let me explain what I mean by that.

Especially on the moment just after cool down we get a lot of steam in the grow rooms for humidity to keep the right, set humidity level. That also brings in a lot more heat in the room and especially in summer period that will give extra demand on your cooling. After some time, you will see in the computer that not only the steam valve will keep opening but the cooling as well, one will bring in humidity, the other will bring it down. The result is loss of energy and not a pleasant climate in the room with a RH level variating from very high too low, due to a lot of steam used by the climate control unit. It will be more visible under the air bags, where the steam comes out, and the RH on the growing surface will be higher. The mycelium will continue to grow there, if you compare it with the rest of the room, and less pins will grow out on those spots.

By simply wetting the floor the first 3 days after cool down you can minimize the steam by bringing in the extra moisture with the wet floors. You can do that 3 times/day if needed. Watch the steam demand in your climate computer and that will tell you if you need to wet the floor.

Erik de Groot
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After the last water during the incubation in the casing soil, the grower wants the mycelium to grow onto the surface.
To ensure a good recovery of the mycelium in this period the right settings for the room climate are essential.
An RH at a minimum of 95%. A very slow air speed, if possible zero and an adequate room temperature. That room temperature should be as close to the optimum for vegetative growth as possible. That optimum temperature is 25° C to 26° C.
This means often a room temperature of around 21° as a minimum.
Then the mycelium has the right conditions to grow onto the surface.
The next question is: how high do I let it grow ?
Higher means better control of the number of primordia, so no surprises about the number of mushrooms growing out. Higher also means easier picking so a higher pick rate. Another positive experience is that clustering is easier avoided.

But the big dis-advantage of having the mycelium higher on the surface is that the climate conditions have to be perfect. The influence of the climate onto the mycelium and the primordia is bigger. So one moment of for instance too low RH means that you will lose primordia.
Deeper mycelium is also easier to stagger the mushrooms so that is an advantage too. Another point is the fact if the grower can stop the mycelium when it grows too high. Overlay as that is called makes the outgrow of primordia more difficult. They come from underneath the blanket of mycelium.

So what determines the choice?
Both ways have their pro’s and con’s.
But for me the crucial point to choose a way is the technical capacity of the farm and the experience of the grower. If you are able to stop the mycelium at all times, still create the stagger and have perfect control of the environmental conditions, grow white.
If you are not sure of all this, grow deeper into the surface of the casing soil. So grow blacker.
Generally blacker is safer.

Does a higher filling weight give better quality?
The filling weight, i.e. the number of kilos of compost per square metre, should be between 80-95 kg/m2. The general trend is the more compost, the better the mushroom quality. But is that right?
Mushroom growing is all about the difference between air temperature and compost temperature, referred to by growers as activity. Activity is essential to grow good quality mushrooms. As the compost is warmer than the air, moisture is released in the form of evaporation. This caused the mushrooms to grow.

Managing activity
Managing activity is key to mushroom growing. So too much activity, because the filling weight is too high, results in faster, uncontrollable growth. For example, a first flush that produces 8 to 10 kg/m2 of mushrooms on the third day. The quality has been lost. The compost temperature has risen too quickly to 25-26 degrees Celsius. So any added value of filling that extra kilo of compost has been wasted. Say you had filled 90 kg/m2 of compost. In that case a filling weight of 85 kg/m2 would have been a better choice. This makes it easier to manage and control activity.

Casing soil
The casing soil on the compost plays a significant role here. The more activity there is, the more the casing soil dehydrates. This means that more mycelium grows in the casing soil. Dried out casing soil cannot absorb water, and neither can mycelium. What is left is dry casing soil that disrupts the water transport from the compost to the mushrooms. The casing soil effectively acts as insulation blanket. So there is activity, but little growth.

Best production
I see the highest yields and the best quality, from the first to the third flush, in situations where compost activity is well managed and controlled and the casing soil stays soft and wet.

Mark den Ouden

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