CVG vs coir-only substrate — is vermiculite actually necessary?
29 replies · Cultivation
I've seen a few growers skip vermiculite entirely and just use hydrated coco coir as their bulk substrate. Their grows look fine. Is vermiculite actually doing something important, or is it one of those 'traditional' steps that's hard to eliminate because nobody bothers to test it?
Vermiculite serves a real function — it acts as a water reservoir, holding moisture between the coir particles and releasing it slowly as the mycelium consumes water. Coir-only dries out faster, especially in low-humidity grows. The gypsum in CVG also improves structure. Both are doing something. Whether they're necessary for a successful grow is another question — many people grow fine without them.
I've done parallel tubs — CVG vs coir-only with identical conditions. CVG produced heavier first and second flushes, about 15% more total weight. Vermiculite also makes field capacity easier to judge. Coir-only is more forgiving of overwatering though — the vermiculite layer can become anaerobic if too wet.
The gypsum matters more than people think. It buffers pH and improves substrate structure for pinset density. I skip vermiculite sometimes but never skip gypsum.
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