Mixing CVG that hits field capacity every time

Substrate · 6 min read · By Aaron Pham

CVG is coco coir, vermiculite, and gypsum. It's popular because it's cheap, clean, and forgiving. The one part people get wrong is water. Too dry and colonization stalls. Too wet and bacteria take over before the mycelium does.

The base recipe

  • 650 g coco coir brick
  • 8 qt vermiculite
  • 1 cup gypsum
  • About 4 to 4.5 qt boiling water, added in stages

That batch makes roughly 15 qt of finished substrate. The CVG calculator scales it to your tub and spawn ratio.

Pasteurize with the water

Break the brick into a bucket with a lid, pour in most of the boiling water, and close it. Wait 20 minutes while the coir expands, then add the vermiculite and gypsum and mix. Close the lid and let it cool for several hours, ideally overnight. This pasteurizes the mix, which is all CVG needs. Fully sterilizing it removes the harmless microbes that help it resist contamination.

The squeeze test

Once it's cool, grab a handful and squeeze hard. At field capacity, a few drops come out. A steady stream means it's too wet: mix in more dry vermiculite. If nothing comes out and the mix crumbles, add a little more water and test again.

Spawning to it

Break up fully colonized grain, mix it through the CVG, level it, and top with a thin layer of substrate. At a 1 : 2 spawn ratio, a 66 qt tub with a 4 inch bed takes about 6 qt of grain and 12 qt of CVG.