Substrate & Preparation

Gypsum

Calcium sulphate amendment that loosens structure and buffers pH.

Typical specifications
Typical dose	2 – 5% of dry substrate
Chemical form	Calcium sulphate dihydrate
pH effect	Neutral — no swing
Grade	Fine powder, agricultural
Dissolves	Sparingly — that is the point
Overdose	Reduce if blocks become crumbly

Substrate & PreparationSmall to large batches

Overview

Agricultural gypsum, or calcium sulphate, is added in small amounts to bulk substrate. It keeps particles from matting together so water and air move freely, and it supplies calcium and sulphur without shifting pH the way lime does. It is a small addition with an outsized effect on structure.

Primary stage: Colonization

Where it fits in the grow

Mixed into dry substrate before hydration and sterilisation.

Safety & handling

Use the agricultural grade only. Builder's or industrial gypsum may contain additives and is not food-safe for this purpose.

Practical advice

Add gypsum to the dry ingredients and mix before adding water. It distributes far more evenly through dry sawdust than through a wet, clumped mix.

Educational only. Mycelium Works does not sell this or any other product, and we receive no payment for listing it. Specifications vary by manufacturer — always follow the maker’s instructions and local regulations.

Gypsum

Overview

Where it fits in the grow

Practical advice

Tools that pair with this

Hardwood Sawdust

Coco Coir

Vermiculite

Substrate Mixing Tub