# A/B nutrient

> An A/B nutrient is a mineral feed split into two concentrates so that calcium (part A) is kept apart from sulfate and phosphate (part B), which would precipitate together.

- Canonical: https://genetixbay.com/knowledge/glossary/a-b-nutrient.html
- Also written: two-part nutrient, 2-part nutrient, A and B, part A part B, A+B, two-part feed
- 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"

An A/B nutrient is a complete mineral feed sold or mixed as two separate concentrates. Part A usually contains [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), often with [potassium nitrate](https://genetixbay.com/knowledge/glossary/potassium-nitrate.md) and [iron chelate](https://genetixbay.com/knowledge/glossary/iron-chelate.md). Part B contains the [phosphates](https://genetixbay.com/knowledge/glossary/phosphate.md), sulfates and the remaining [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md). Kept apart in concentrated form, they stay clear; mixed together at concentrate strength, calcium phosphate and calcium sulfate drop out as sludge.

## In practice

Add part A to the water, stir, then add part B, never pouring one concentrate straight into the other. Equal doses of A and B are typical, but check the label. The limitation is that both parts scale together: cutting the dose to reduce nitrogen also reduces everything else. That is why [per-element dosing](https://genetixbay.com/knowledge/glossary/per-element-dosing.md) exists, and why a late-flower [nitrogen taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) is hard to run with a bottled two-part alone.

## Don't confuse with

- **One-part nutrient**: a single concentrate that avoids the precipitation problem by formulation.
- **Bloom and grow bottles**: a stage split, which may or may not also be an A/B split.
- **A/B testing**: a trial method, not a feed.

## Related terms

[One-part nutrient](https://genetixbay.com/knowledge/glossary/one-part-nutrient.md), [Stock solution](https://genetixbay.com/knowledge/glossary/stock-solution.md), [Calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md), [Magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.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)
- [Per-element feeding tricks: what growers adjust, stage by stage](https://genetixbay.com/knowledge/nutrients/per-element-tricks.md)

## Sources

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