# Perlite

> Perlite is a light, white, puffed volcanic glass added to growing mixes to increase drainage and air space; it is chemically inert and holds no nutrients.

- Canonical: https://genetixbay.com/knowledge/glossary/perlite.html
- Also written: perlite rock, expanded perlite, sponge rock
- 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"

Perlite is volcanic glass heated rapidly until trapped water flashes to steam and the grains pop like [popcorn](https://genetixbay.com/knowledge/glossary/popcorn-buds.md) into light, porous white granules. In a mix it creates large pores that [drain](https://genetixbay.com/knowledge/glossary/runoff.md) quickly and fill with air, raising the [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) of the medium. It is essentially inert, near neutral [pH](https://genetixbay.com/knowledge/glossary/ph.md), and supplies no nutrients.

## In practice

Common blends are 10-30% perlite in soil or [peat](https://genetixbay.com/knowledge/glossary/peat.md) mixes and 20-40% in [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). More perlite means faster drainage and more frequent watering. It floats to the surface over time and can be blown about when dry; wet it before mixing and wear a dust mask, since the fine dust is an irritant. It does not break down, so it can be reused after cleaning.

Pumice does a similar job, is heavier and does not float.

## Don't confuse with

- **Vermiculite**: also expanded mineral, but it holds water and nutrients; the opposite job.
- **Clay pebbles**: larger aggregate used as a hydro medium on its own.

## Related terms

[Vermiculite](https://genetixbay.com/knowledge/glossary/vermiculite.md), [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [Potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Overwatering](https://genetixbay.com/knowledge/glossary/overwatering.md)

## Read more

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