# Nutrient lockout

> Nutrient lockout is when plants show deficiency symptoms although nutrients are present, because pH, salt build-up, ion antagonism or damaged roots stop uptake.

- Canonical: https://genetixbay.com/knowledge/glossary/nutrient-lockout.html
- Also written: lockout, locked out, nutrient lock, pH lockout, nutrient lock-out
- Glossary category: pH, EC and water · Evidence: Supported
- 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"

Nutrient lockout is grower shorthand for a plant that cannot take up nutrients that are present in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). It is not one mechanism. The common causes are root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) outside the working range (iron and manganese become insoluble at high pH, calcium and magnesium less available at low pH), [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) and [osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md), antagonism between ions (excess potassium suppressing magnesium and calcium, for example) and roots damaged by rot, overwatering, heat or low oxygen.

## In practice

The classic error is to add more of the "missing" nutrient, raising [EC](https://genetixbay.com/knowledge/glossary/ec.md) and making things worse. Diagnose first, cheapest checks first:

1. Measure root-zone pH ([runoff](https://genetixbay.com/knowledge/glossary/runoff.md) or PourThru), not just input pH.
2. Compare runoff EC with input EC.
3. Inspect roots: white and firm is good; brown, slimy or smelly is a root problem, not a nutrient one.
4. Review the feed recipe for extreme ratios.

Then fix the cause: correct pH, do a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) if runoff EC is high, and restore root health. New growth should come in clean within one to two weeks; damaged leaves will not recover.

## Don't confuse with

- **True deficiency**: the element is genuinely short in the feed.
- **Nutrient antagonism**: one specific cause of lockout.

## Myth check

GenetixBay house position: a **root-zone flush** to wash accumulated salts out of the medium is the one valid [flush](https://genetixbay.com/knowledge/glossary/flushing.md). It treats the medium, not the plant, and can be done at any stage. A **pre-harvest flush** is a *Myth* and actively harmful: it starves the plant while it is packing on its final weight and resin. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md).

## Related terms

[pH](https://genetixbay.com/knowledge/glossary/ph.md), [Salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), [Osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md), [Nutrient antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md), [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md)

## Read more

- [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)
- [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md)
- [How to diagnose any cannabis plant problem](https://genetixbay.com/knowledge/diagnosis/how-to-diagnose-any-problem.md)

## Sources

1. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9
2. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf