# Auxin

> A class of plant hormones, chiefly indole-3-acetic acid (IAA), that drives cell elongation, apical dominance, bending toward light and root formation.

- Canonical: https://genetixbay.com/knowledge/glossary/auxin.html
- Also written: auxins, IAA, indole-3-acetic acid, IBA, indole-3-butyric acid, NAA
- Glossary category: Plant biology · 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"

Auxins are plant hormones that regulate growth and shape. The main natural auxin is indole-3-acetic acid (IAA), made mostly in young leaves and [shoot tips](https://genetixbay.com/knowledge/glossary/apical-meristem.md) and moved down the stem by polar transport. Auxin promotes cell elongation, maintains [apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), causes phototropism and gravitropism, and triggers adventitious and lateral root formation.

## In practice

Two everyday uses for growers:
- **Training**: topping removes the main auxin source, so side buds wake up. Bending a stem changes auxin flow, which is part of why [LST](https://genetixbay.com/knowledge/glossary/lst.md) evens out a canopy.
- **Cloning**: rooting products use synthetic or related auxins, mainly indole-3-butyric acid (IBA) and sometimes NAA, as gels, powders or dips. In cannabis, IBA treatment improved rooting of cuttings in controlled trials (Caplan et al. 2018).

Auxin works in balance with [cytokinin](https://genetixbay.com/knowledge/glossary/cytokinin.md): high auxin relative to cytokinin favours roots; high cytokinin favours shoots. That ratio is the core of tissue-culture media.

Rooting products are concentrates of plant-growth regulators. Follow label rates and wear gloves.

## Don't confuse with

- **Cytokinin**: promotes shoot and bud growth, opposing apical dominance.
- **Gibberellin**: drives [internode](https://genetixbay.com/knowledge/glossary/internode.md) elongation and [stretch](https://genetixbay.com/knowledge/glossary/stretch.md).
- **Fertiliser**: supplies nutrients; hormones are signals, not food.

## Related terms

[Apical dominance](https://genetixbay.com/knowledge/glossary/apical-dominance.md), [Cytokinin](https://genetixbay.com/knowledge/glossary/cytokinin.md), [Gibberellin](https://genetixbay.com/knowledge/glossary/gibberellin.md), [Apical meristem](https://genetixbay.com/knowledge/glossary/apical-meristem.md)

## Read more

- [Topping: cutting the main tip for more colas](https://genetixbay.com/knowledge/training/topping.md)

## Sources

1. Taiz L, Zeiger E, Møller IM, Murphy A. 2015. Plant Physiology and Development, 6th edition. Sinauer Associates.
2. Caplan D, Stemeroff J, Dixon M, Zheng Y. 2018. Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science 98(5):1126-1132. https://doi.org/10.1139/cjps-2018-0038