# Calcium chloride

> Calcium chloride (CaCl2) adds calcium without nitrogen, useful for late-flower nitrogen tapering, but it adds chloride, so doses must stay modest.

- Canonical: https://genetixbay.com/knowledge/glossary/calcium-chloride.html
- Also written: CaCl2, CaCl2·2H2O, calcium chloride dihydrate
- 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"

Calcium chloride is a very soluble salt of calcium and [chloride](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md). The anhydrous form is about 36% Ca; the more common dihydrate (CaCl2·2H2O) is about 27% Ca and 48% Cl. It is strongly hygroscopic and releases heat as it dissolves.

## In practice

Its main use in cannabis feeds is supplying calcium when the grower wants to cut nitrogen, such as during a late-flower [N taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md), since [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md) brings N along. The trade-off is chloride. Small amounts are harmless, but heavy use raises chloride enough to burn leaf margins. Many growers split the job: calcium chloride for part of the Ca, gypsum or reduced calcium nitrate for the rest. Food-grade or reagent grade avoids the contaminants in de-icing salt.

## Units and formula

1 g/L of the dihydrate gives about 273 mg/L (ppm) Ca and 482 mg/L Cl.

## Don't confuse with

- **Calcium nitrate**: the standard calcium source, with nitrogen.
- **Road de-icing salt**: may be calcium chloride but contains impurities.
- **Calcium sulfate (gypsum)**: low solubility, adds [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) instead of chloride.

## Related terms

[Calcium](https://genetixbay.com/knowledge/glossary/calcium.md), [Chlorine (nutrient)](https://genetixbay.com/knowledge/glossary/chloride-nutrient.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md)

## Read more

- [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)
- [Calcium (Ca) in cannabis: deficiency, transport, targets and sources](https://genetixbay.com/knowledge/nutrients/calcium.md)
- [Chlorine and chloride (Cl) in cannabis: a micronutrient you never need to add](https://genetixbay.com/knowledge/nutrients/chlorine.md)

## Sources

1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6
2. 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