# Vermiculite

> Vermiculite is expanded mica-like mineral flakes that hold water and nutrients in a mix, used to increase moisture retention rather than drainage.

- Canonical: https://genetixbay.com/knowledge/glossary/vermiculite.html
- Also written: exfoliated vermiculite, vermiculite mix
- Glossary category: Systems and media · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Vermiculite is a hydrated silicate mineral that, when heated, expands into light, accordion-like flakes. Unlike [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), it soaks up water and has a high [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), so it holds potassium, calcium, magnesium and [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) on its surfaces. It is used in seed-starting mixes and in soils where more water holding is wanted.

## In practice

Growers add 10-20% vermiculite to sandy or very open mixes, or use it in seed starting and [cloning](https://genetixbay.com/knowledge/glossary/cloning.md) mixes. Too much in a [container mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) reduces [air space](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) and can make the medium stay wet for long periods. Some older vermiculite from specific mines was contaminated with asbestos; modern horticultural grades are tested, but avoid breathing dust from any dry mineral product.

## Don't confuse with

- **Perlite**: adds air and [drainage](https://genetixbay.com/knowledge/glossary/runoff.md); vermiculite adds water and nutrient holding.
- **Mica**: the related mineral family; not used directly as a medium.

## Related terms

[Perlite](https://genetixbay.com/knowledge/glossary/perlite.md), [Cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), [Potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), [Field capacity](https://genetixbay.com/knowledge/glossary/field-capacity.md)

## Read more

- [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md)

## Sources

1. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5