Substrate & Preparation

Vermiculite

A lightweight mineral that holds water and keeps casing open.

Typical specifications
Grade	Fine, medium, coarse
Water absorption	3 – 4x its own weight
Role	Casing and moisture retention
Nutrition	None — inert
Typical mix	50% coir / 50% vermiculite
pH	Near neutral

Substrate & PreparationSmall to large batches

Overview

Vermiculite is an expanded mica that absorbs several times its weight in water and releases it slowly. It is used as a casing layer, as a moisture reservoir in substrate mixes, and to keep the surface of a block humid without suffocating it. It contributes no nutrition, so it never invites contamination.

Primary stage: Fruiting

Where it fits in the grow

Blended into substrate or applied as a casing layer before fruiting.

Safety & handling

Dry vermiculite is dusty. Wear a mask when pouring, and moisten it before mixing to keep fines out of the air.

Practical advice

For a casing layer, aim for a thin 1–2 cm band. A thick casing buries pins and delays the first flush substantially.

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.

Vermiculite

Overview

Where it fits in the grow

Practical advice

Tools that pair with this

Coco Coir

Gypsum

Substrate Mixing Tub

Humidity Tent