the_chosen_one said:

There's not much expansion with verm IME. Even the large chunks tend to stay about the same size. There's loft between the layers and I'd bet that's where most of the water goes.

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Synack said:

At the risk of walking into the flames I'm gonna ask this and probably regret it..

Is is possible that the additional water retention capacity of vermiculite vs. coir could reduce the degree of substrate shrink as water is consumed by the first flush or--relatedly--potentially make it easier to rehydrate the sub for later flushes?

My reasoning here is that verm, being able to retain more water than coir by weight, being lighter than coir, and having greater volume to weight, could result in the substrate being less dense after having the water sucked out of it by the first flush, and potentially leaving a more open (spongy?) structure to the cake that would allow [more] water to penetrate and be re-absorbed more easily.

For the record, I'm not *recommending* or *suggesting* anything here, just asking out of academic curiosity.

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Arkyhog said:

Hey, I found some really cool stuff about vermiculite and perlite in the link below! I thought the table was super interesting too!

The "grade" or size of the vermiculite flakes significantly impacts how much water it holds. Smaller particles (finer grades) have more surface area and typically hold more water than large, chunky flakes.

Grade Particle Size Water-Holding Capacity
Fine 1.0mm – 3.0mm 40% – 50% (Highest retention)
Medium 2.0mm – 5.0mm 35% – 40% (General potting)
Coarse 5.0mm – 10.0mm 30% – 35% (Best for aeration)

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cronicr said:

No not really, your substrate doesn't shrink due to water loss it shrinks because it's being eaten otherwise it would expand again once dunked

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cronicr said:

The issues with retesting after a flush is when we first spawn our grain is the first thing to absorb moisture , then everything colonizes and ultimately fruits but where as the at spawn your substrate was just coir/verm/grain at your second flush your substrate is now all the above plus mycelium which is largely hydrophobic and water resistant for x amount of time

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Synack said:

cronicr said:

The issues with retesting after a flush is when we first spawn our grain is the first thing to absorb moisture , then everything colonizes and ultimately fruits but where as the at spawn your substrate was just coir/verm/grain at your second flush your substrate is now all the above plus mycelium which is largely hydrophobic and water resistant for x amount of time

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But if the test is just uncolonized mixtures of coir/verm, wouldn't we expect the results (assuming they were favorable in the first place) to still be directionally correct when scaled up to an actual grow?  Some portion of the post-flush substrate being myc and decomposed coir would mean less effect relative to the uncolonized test, but plenty of that sub would still be usable coir and verm..

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tryptkaloids said:

Im not sure myc is actually eating verm, but i kinda agree. The extra mass of fruits doesn't come from nowhere.

Side note - I find super fine verm to be denser than i like when hydrated

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cronicr said:

So weigh your mushrooms , take 90 percent of that number and dump it back in lol ,it won't expand it won't absorb it all , it's digesting your substrate that's where your CO2 comes from it's also constricting it but of you have ever seen a substrate go a few flushes it gets comically small .I mean there's definitely a few percent of that from water loss but but it will never absorb that same amount again because there ain't the same amount of substrate there anymore

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