# Growing medium

> A growing medium (plural media) is the material roots grow in, such as soil, coco, rockwool or clay pebbles, which anchors the plant and holds water, air and sometimes nutrients.

- Canonical: https://genetixbay.com/knowledge/glossary/growing-medium.html
- Also written: media, medium, substrate, grow media, growing media, growing substrate
- 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"

A growing medium, or substrate, is whatever the roots grow in. It anchors the plant and holds a balance of water and air; some media (soil, compost, peat, coco) also hold and supply nutrients, while others (rockwool, perlite, [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md)) are nearly inert. "Media" is the plural.

## In practice

Media are judged by a few properties: water-holding capacity, [air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), salt content (starting [EC](https://genetixbay.com/knowledge/glossary/ec.md)), stability over time and cleanliness. These decide how often to water, how to feed, and how forgiving the system is. Soil and amended mixes buffer mistakes; inert media give fast, precise control but punish errors quickly.

Choosing a medium is the first and most important systems decision: see [choosing a system](https://genetixbay.com/knowledge/systems/choosing-a-system.md).

## Don't confuse with

- **Root zone**: the environment around the roots, including solution and microbes.
- **Medium (DWC)**: in water culture the "medium" in the [net pot](https://genetixbay.com/knowledge/glossary/net-pot.md) only anchors the plant; roots live in solution.

## Related terms

[Soil](https://genetixbay.com/knowledge/glossary/soil.md), [Coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), [Rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md), [Soilless](https://genetixbay.com/knowledge/glossary/soilless.md), [Air-filled porosity](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md), [Cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md)

## Read more

- [Choosing your growing system: soil, coco, rockwool or hydro](https://genetixbay.com/knowledge/systems/choosing-a-system.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