# Chlorine (nutrient)

> As a plant nutrient, chlorine is used as the chloride ion (Cl-) in tiny amounts for photosynthesis and osmotic balance; excess from water or salts is the usual problem.

- Canonical: https://genetixbay.com/knowledge/glossary/chloride-nutrient.html
- Also written: Cl, Cl-, chloride, chloride nutrient, chloride toxicity
- Glossary category: Nutrients · 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"

Chlorine is an essential [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), taken up and used as the chloride ion (Cl-). It helps the water-splitting step of [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md), balances charge and osmotic pressure in cells and supports stomatal movement. Chloride is highly mobile and is present almost everywhere, so true [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) is rare.

## In practice

The practical issue is excess. Tap water, coco that was not washed, [calcium chloride](https://genetixbay.com/knowledge/glossary/calcium-chloride.md) or potassium chloride, and some organic inputs can push chloride high enough to burn leaf margins and tips, starting on older leaves. Moderate chloride is tolerated; problems tend to appear when it climbs into the low hundreds of mg/L (ppm). A water report or runoff test shows where it comes from.

## Don't confuse with

- **Chlorine as water treatment**: dissolved chlorine gas or [hypochlorite](https://genetixbay.com/knowledge/glossary/free-chlorine.md) used as a disinfectant, a separate topic covered in [pH](https://genetixbay.com/knowledge/glossary/ph.md) and water quality.
- **Chloramine**: a longer-lasting disinfectant in many municipal supplies.
- **Nutrient burn**: [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) from total [EC](https://genetixbay.com/knowledge/glossary/ec.md) rather than chloride specifically.

## Related terms

[Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Calcium chloride](https://genetixbay.com/knowledge/glossary/calcium-chloride.md), [Sodium](https://genetixbay.com/knowledge/glossary/sodium.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md), [Mobile nutrient](https://genetixbay.com/knowledge/glossary/mobile-nutrient.md)

## Read more

- [Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add](https://genetixbay.com/knowledge/nutrients/chlorine.md)
- [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md)

## Sources

1. White PJ, Broadley MR. 2001. Chloride in soils and its uptake and movement within the plant: a review. Annals of Botany 88(6):967-988. https://doi.org/10.1006/anbo.2001.1540
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