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Nutrient Lockout: When Feeding More Makes It Worse
By the Cultivar grow team · published 2026-08-04 · updated 2026-08-04 · how we source these numbers
Lockout is the reason "add more nutrients" is such a destructive default. The plant looks hungry — pale, yellowing, spotted, stalling — and everything about the symptom invites feeding. But if the cause is lockout, feeding raises the salt concentration around roots that already cannot absorb what is there, and the plant gets worse in a way that looks like it needed even more food.
Deficiency and lockout are visually identical. Only measurement separates them.
The two-measurement diagnosis
Water with plain pH-corrected water, catch the runoff, and read two numbers.
| Runoff pH | Runoff EC | Verdict |
|---|---|---|
| In range | Low, near input | Genuine deficiency — feed |
| Out of range | Anything | Lockout — correct pH |
| In range | Well above input | Salt lockout — flush |
| Out of range | Well above input | Both — flush, then correct pH |
Target ranges, matching our pH chart: soil 6.3–6.8, coco 5.8–6.2, hydro 5.5–6.0.
That is the whole diagnosis. Without those two numbers you are guessing, and the guess is wrong roughly half the time.
Why pH controls everything
Nutrient availability is chemistry, not biology. Each nutrient is soluble and absorbable within a band of pH, and outside that band it stays in the pot in a form roots cannot take up. Micronutrients in particular fall off sharply as pH rises — iron, manganese and zinc become progressively unavailable in alkaline conditions.
This produces the signature frustration of lockout: a grower adds iron, sees no change, adds more, and still sees nothing, because the iron was never the limiting factor. pH was.
Why salts cause the other half
Roots draw water in by osmosis, against the concentration of dissolved salts around them. As that concentration climbs, the gradient the plant is working against gets steeper, and at some point uptake effectively stalls. The plant is surrounded by food and starving.
Salt accumulation is usually a watering habit rather than a feeding strength problem — see nutrient burn, which is the same underlying cause showing a different face. Watering to saturation without meaningful runoff leaves every gram of salt you added in the pot, and it compounds week over week.
Fixing it
If pH is out of range:
- Correct the pH of your input water and feed solution.
- Water normally and re-measure runoff over the next two or three waterings.
- Expect the runoff to move toward range gradually rather than instantly.
Do not chase runoff pH by wildly over-correcting input pH. Adjust input into the correct range and let the medium follow.
If runoff EC is high:
- Flush with plain pH-corrected water at roughly two to three times the pot's volume, slowly.
- Measure runoff EC as you go and stop when it approaches input EC.
- Let the pot dry properly before feeding again. A flush that leaves the medium saturated for days trades a salt problem for an oxygen problem — see drooping leaves.
- Resume feeding at reduced strength.
If both: flush first, then correct pH, then dry, then feed.
Media behave differently
Soil buffers pH, so it drifts slowly and recovers slowly. Lockout in soil usually builds over weeks and takes more than one watering cycle to clear.
Coco has almost no buffering and holds calcium poorly, so pH can swing fast. Coco growers generally feed at every watering and need to watch runoff more closely, not less.
Hydro gives you direct control and the fastest correction — but also the fastest failure, because there is no medium to absorb a mistake. Check reservoir pH daily; it drifts as the plant feeds.
Preventing recurrence
- Water to real runoff every time, in the region of 10–20% excess, so salts leave rather than accumulate.
- Measure runoff pH and EC weekly, not only when something looks wrong. The trend warns you before the leaves do.
- Calibrate the pH pen. An uncalibrated pen drifts and will confidently tell you everything is fine.
- Do not stack supplements without accounting for what each adds to total EC.
Judging the fix
Watch new growth, not damaged leaves — those stay damaged.
- New leaves emerging with normal colour and no spotting.
- Symptoms not spreading to previously healthy foliage.
- Growth rate picking back up.
Allow one to two weeks. If new growth is still symptomatic after that, re-measure rather than repeating the flush; a second flush on a pot that is already clean only waterlogs the roots.
The habit that prevents most of this
Buy the pH pen before the nutrients. Nearly every grower arrives at that conclusion eventually, usually after a season of adding supplements that could not possibly have worked. It is the cheapest instrument in the tent and it answers the question that decides whether any of the others matter.
- Digital pH pen + calibration solution — lockout is a pH problem far more often than anything else, and you cannot see pH
- EC / TDS meter — distinguishes salt-driven lockout from a genuine shortfall in about a minute
- pH up / pH down solution — correcting input pH is the actual fix once you know which way it has drifted
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FAQ
What is nutrient lockout?
The nutrients are present in the medium but the plant cannot absorb them. Usually pH has drifted outside the range where a given nutrient is chemically available, or accumulated salts have raised the root-zone concentration so high that uptake stalls. The plant shows deficiency symptoms while sitting in plenty of food.
How do I know if it is lockout or a real deficiency?
Measure runoff pH and EC. Deficiency symptoms with in-range pH and LOW runoff EC means a genuine shortfall — feed. The same symptoms with out-of-range pH, or with runoff EC well above what you put in, means lockout — flush.
How do I fix nutrient lockout?
Flush with plain pH-corrected water at two to three times the pot volume until runoff EC approaches input EC and runoff pH lands in range. Let the pot dry properly, then resume feeding at reduced strength.
How long does recovery from lockout take?
New growth should look normal within one to two weeks. Existing damaged leaves do not recover. If new growth is still symptomatic after two weeks, the pH has probably drifted back out and you should re-measure rather than re-flush.
What pH should my runoff be?
Roughly 6.3 to 6.8 in soil, 5.8 to 6.2 in coco, and 5.5 to 6.0 in hydro. Runoff reads a little differently from input, so track the trend across waterings rather than fixating on a single number.
Keep reading
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- Drooping Cannabis Leaves: Overwatered or Underwatered?
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