# Humic acid

> Humic acid is a large, dark organic fraction of decomposed matter that binds nutrients and may modestly aid root growth; effects in cannabis are small and inconsistent.

- Canonical: https://genetixbay.com/knowledge/glossary/humic-acid.html
- Also written: humic acids, humates, humic substances, potassium humate, leonardite extract
- Glossary category: Nutrients · Evidence: Contested
- 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"

Humic acid is the part of humic substances that dissolves in alkaline solution but precipitates when acidified. It is a mix of large, complex organic molecules from decomposed plant matter, usually extracted from leonardite, [peat](https://genetixbay.com/knowledge/glossary/peat.md) or lignite. It binds metal ions and adds [cation exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md).

## In practice

Growers add humic products to soil and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) as a "root stimulant". In soil it can improve structure, water holding and [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) availability. Bernstein and colleagues tested humic acid supplementation on [medical cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md) and found effects on the plant's chemical profile were limited compared with N, P and K changes. In hydro, humic acid can stain reservoirs, foam and precipitate at low [pH](https://genetixbay.com/knowledge/glossary/ph.md), and may feed biofilm. Expect modest effects at best (Evidence: Contested).

## Don't confuse with

- **Fulvic acid**: the smaller fraction that stays soluble at any pH.
- **Compost tea**: a microbial brew, not an extract.
- **Humus**: the stable organic matter in soil as a whole.

## Related terms

[Fulvic acid](https://genetixbay.com/knowledge/glossary/fulvic-acid.md), [Chelate](https://genetixbay.com/knowledge/glossary/chelate.md), [Organic fertiliser](https://genetixbay.com/knowledge/glossary/organic-fertiliser.md), [Biostimulant](https://genetixbay.com/knowledge/glossary/biostimulant.md)

## Read more

- [Organic vs mineral nutrition for cannabis: what the trials show](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md)

## Sources

1. Bernstein N, Gorelick J, Zerahia R, Koch S. 2019. Impact of N, P, K, and humic acid supplementation on the chemical profile of medical cannabis (Cannabis sativa L). Frontiers in Plant Science 10:736. https://doi.org/10.3389/fpls.2019.00736
2. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9