# How do I fix nutrient lockout?

> Fix nutrient lockout by finding its cause first: most lockout is root-zone pH out of range, salt build-up or damaged roots, not true antagonism. Calibrate your meter, check runoff pH and EC, and look at the roots. If runoff EC is about 0.8-1.0 mS/cm or more above input, flush the root zone with 2-3 times the pot volume, then resume normal feeding. Correct pH gradually and stop stacking boosters.

- Canonical: https://genetixbay.com/knowledge/answers/how-to-fix-nutrient-lockout.html
- Topic: Nutrients · Type: Troubleshooting
- Evidence: Supported · Status: Draft: awaiting expert review
- Full article: [Nutrient antagonism and Mulder's chart: what the evidence actually says](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md)
- Also asked as: How do I fix lockout? | My plant is not taking up nutrients | Should I flush for lockout? | Deficiency even though I'm feeding | What causes nutrient lockout?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

Find the cause before you treat it. Most "[lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md)" is root-zone [pH](https://genetixbay.com/knowledge/glossary/ph.md) out of range, [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md) or failing roots, not a nutrient fight. If [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md) sits about 0.8–1.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) or more above what you feed, [flush](https://genetixbay.com/knowledge/glossary/flushing.md) the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) with 2–3 times the [pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md), then go straight back to normal feeding. *Supported.*

## Why

pH controls solubility. At high pH iron, manganese and zinc drop out of solution; at low pH calcium and magnesium uptake falls [3][4]. Alkaline water pushes the root zone up week by week even if you pH every feed [3].

Real [antagonism](https://genetixbay.com/knowledge/glossary/nutrient-antagonism.md) exists but is narrower than charts suggest. A review of 117 interactions found synergy far more often than antagonism; the ones that matter are among the cations [1]. In cannabis, high potassium supply lowered calcium and magnesium uptake [2], which is what stacked PK boosters do.

Salt build-up raises root-zone EC until roots struggle to take up water and ions. That is the one case where a flush helps, because it treats the medium.

## The numbers

| Check | Normal | Act if |
|---|---|---|
| Runoff pH, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) or rockwool | 5.8–6.5 | Outside, or >0.5 from input and rising |
| Runoff pH, soil | 6.0–7.0 | Below 5.8 or above 7.3 |
| [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) vs input | Equal to +0.5 mS/cm | +0.8–1.0 mS/cm or more |
| Roots | White to cream, firm | Brown, slimy, smelly |

## What to do

1. Calibrate the [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) in fresh pH 7 and [pH 4 buffer](https://genetixbay.com/knowledge/glossary/calibration-solution.md).
2. Measure input and runoff pH and EC.
3. Check roots and watering: soggy pots and rot mimic lockout.
4. Salty root zone: flush 2–3× pot volume, slowly, then feed normally.
5. pH off: correct the input gradually; acidify alkaline water.
6. Stop stacking boosters and [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) on a complete base.

## Common mistakes

- Flushing with plain water for every [leaf spot](https://genetixbay.com/knowledge/glossary/leaf-spot.md).
- Adding more of the "missing" nutrient, which raises EC further.
- Trusting an uncalibrated pen.
- Expecting damaged leaves to turn green again.

## Related

- Full article: [Nutrient antagonism and Mulder's chart](https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.md)
- Articles: [runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md) · [pH and availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)
- Answers: [do I need to pH?](https://genetixbay.com/knowledge/answers/do-i-need-to-ph-my-water.md) · [do damaged leaves recover?](https://genetixbay.com/knowledge/answers/do-damaged-leaves-recover.md)
- Terms: [nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md) · [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md)

## Follow-up questions

**What is nutrient lockout?** Nutrient lockout is when a plant shows deficiencies although the feed contains the nutrient, because the roots cannot take it up. The usual causes are root-zone pH out of range, salt build-up in the medium, damaged or rotting roots, and occasionally a real antagonism such as excess potassium suppressing calcium and magnesium. Measure before guessing.

**How do I flush for lockout?** To flush for lockout, record input and runoff pH and EC, then run about 2-3 times the container volume through slowly in several passes: pH-adjusted water at about 6.3-6.8 for soil, or a light solution at EC 0.4-0.8 mS/cm with calcium and magnesium at pH 5.8-6.0 for coco. Stop when runoff EC is within 0.3-0.5 of input, then feed normally.

**How long does it take a plant to recover from lockout?** Once the root zone is back in range, new growth usually looks normal within about a week, which is grower experience rather than a tested figure. Damaged leaves stay damaged, so judge recovery on the newest growth only. If new leaves still show symptoms after 7-10 days, recheck pH, EC and the roots before adding anything.

## Sources

1. Rietra RPJJ, Heinen M, Dimkpa CO, Bindraban PS, 2017. Effects of nutrient antagonism and synergism on yield and fertilizer use efficiency. Communications in Soil Science and Plant Analysis 48(16):1895-1920. https://hub.ifdc.org/handle/20.500.14297/2410
2. Saloner A, Sacks MM, Bernstein N, 2019. Response of medical cannabis (Cannabis sativa L.) genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369
3. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf
4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9