(Tippin gets out the massive reference manual, to answer this one)
That is fairly common. Because, the first flush substrate did not contain optimal moisture level.
First flush many pins. Substrate cannot pump enough nutrient/moisture to all of them. So, they are smaller.
Second flush, fewer pins. Substrate can pump more nutrient moisture to all of them. So, they are larger.
Assuming your substrate moisture level is near optimal (68/72% saturated)at spawning. The moisture level will decrease as the tray colonizes, by assimilation, respiration, and evaporation.
Then, you add a hydrated casing mix, and generally expose the tray to fruiting conditions quickly.
The reality most often is, you did not replace all the moisture the substrate lost during colonization. You simply blanketed the substrate with a moist casing layer, then quickly exposed the tray to FAE & cycled light exposure.
Consequently, the substrate does not usually have time to replenish itself, from the additional moisture the casing mix added.
The point being, once a tray is fully colonized, it is better to add a casing layer, then continue incubation, without pinning triggers, for a few days. Which will allow the substrate time to replenish itself, from the additional moisture, the casing layer provides.
Secondly, there is a school of thought, that cased substrate trays, will do fine at 70 to 80% Rh.
I beg to differ.
IMO, They will do better,as primordia forms, at 90% + Rh.
The reason why is, mushrooms fruit bodies do not have "skin", per se.
A mushroom fruit body breaths, and will assimilate moisture from surrounding air. If it is there, to be had.
Consequently, if you bump Rh up as high as possible, in the pinning/growth stage, without super saturation of the tray content.
Besides what the substrate, and casing layer is providing. You are providing more moisture directly to fruit bodies, as they grow.
Which, will allow them to grow larger.
Think of a fruit body, like a piece of leather.
When moist, it is supple, and will stretch. When dry, it will harden, and not stretch.
The same goes for fruit bodies.
Up to a certain point, the more moisture you provide to the tray, and air the tray is in, the larger fruit bodies can become.
This school of thought was born out by weighing a tray, after spawning.
Then, weighing it again, fully colonized.
Then, adding X amount of hydrated casing mix. Which contained X amount of water weight.
Then, weighing the tray as it begins, and continues to flush.
By doing so, you can determine how much water weight, the tray has lost, and how much should be replaced.
All of which is rather laborious.
So, instead, simply maximize water applications, to the point of saturation, and, pour any excess off.
As well as maximize Rh, during the fruit growth cycles.
Being careful NOT to super saturate a tray.
To much moisture, you drown it. Not enough, you inhibit growth.
Leaning when to apply moisture, and how much is an art form.
-------------------- Perfection is attained by slow degrees; it requires the hand of time... [
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