# Boric acid

> Boric acid (H3BO3) is the usual boron source in micronutrient mixes, about 17.5% boron; plants absorb boron in this same uncharged form.

- Canonical: https://genetixbay.com/knowledge/glossary/boric-acid.html
- Also written: H3BO3, boracic acid, orthoboric acid
- 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"

Boric acid is a weak acid of [boron](https://genetixbay.com/knowledge/glossary/boron.md), about 17.5% B. In normal nutrient solutions most boron exists as uncharged boric acid, which is the main form roots absorb. It dissolves slowly in cold water; warm water helps when making stock.

## In practice

Boron has a narrow window between enough and too much, so boric acid is dosed from a concentrated [micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md) stock, not by the pinch. Final feeds usually aim for about 0.2-0.5 mg/L (ppm) B. Check the water report first: some tap and [well waters](https://genetixbay.com/knowledge/glossary/tap-water.md) already supply a meaningful share. Borax ([sodium](https://genetixbay.com/knowledge/glossary/sodium.md) borate, about 11% B) and solubor-type sodium borates are alternatives but add sodium.

## Units and formula

1 mg/L of boric acid gives about 0.175 mg/L (ppm) B. To reach 0.3 ppm B, add about 1.7 mg/L.

## Don't confuse with

- **Borax**: sodium tetraborate, a different boron salt with sodium.
- **Boric acid as an insecticide**: same chemical, different purpose and dose; never dose a feed from pest-bait products.

## Related terms

[Boron](https://genetixbay.com/knowledge/glossary/boron.md), [Micronutrient](https://genetixbay.com/knowledge/glossary/micronutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Nutrient toxicity](https://genetixbay.com/knowledge/glossary/nutrient-toxicity.md)

## Read more

- [Boron (B) in cannabis: distorted tips, dying roots and a narrow safe window](https://genetixbay.com/knowledge/nutrients/boron.md)
- [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.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. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9