The Unsung Hero of Substrate
Gypsum (calcium sulphate) is easy to overlook, but it plays an important part in successful mushroom growing. It adds calcium and sulphur, two minerals that mycelium uses, and it improves the structure of both substrate and grain. Most growers use it in their CVG mix and when preparing grain spawn.
What Is Included
- 1 x bag of gypsum (500g, 1kg or 2kg)
How to Use Gypsum
- In CVG: add roughly 5 to 10 percent by volume to your coir and vermiculite, or about a cup per 5kg brick of coco coir.
- In grain spawn: add a tablespoon per kilo of dry grain after hydrating. It coats the grains and stops them sticking together, giving better spawn that breaks up easily.
- In hardwood mixes: around 1 to 2 percent helps buffer the pH.
Why We Use It
Our first few batches of homemade rye spawn were sticky, clumped and slow. Adding gypsum after hydration made a noticeable difference. The grains stayed separate and colonised more evenly.
Is It Safe?
Gypsum is a natural mineral and is widely used in agriculture and food production. Wear a dust mask when handling large amounts of fine powder.
Related
Make your own spawn with our millet grain or skip the prep with sterilised CVG. More in mushroom substrate.
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