Cannabis nutrient lockout happens when root zone pH drifts outside the narrow window where your plant can absorb minerals, so nutrients stay in the medium even though you keep feeding. The fix is almost never more fertilizer. It is correcting pH and salt levels first, then letting the plant recover before you push feed again.
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What Nutrient Lockout Actually Is
Nutrients in your bottle are dissolved ions. Those ions only stay available to roots inside a certain pH range. When pH moves above or below that range, some elements bind to medium particles, precipitate out of solution, or get outcompeted by others. The plant keeps showing deficiency symptoms while you keep pouring nutrients in, and the medium keeps holding them.
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There are two common versions. The first is straight pH drift, where your water or feed lands outside the target range. The second is salt buildup from overfeeding, which raises electrical conductivity (EC) in the medium and pulls pH down over time. Both look similar on the leaves.
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The pH Ranges That Matter for Cannabis
Match your target to your growing medium, not to a number you read for a different setup.
- Soil: 6.0 to 7.0, with most growers landing near 6.5.
- Coco coir: 5.8 to 6.3.
- Hydro, DWC, and rockwool: 5.5 to 6.1.
- Peat-based soilless mixes: 5.8 to 6.3.
Check both input and runoff. Input pH tells you what you are pouring in. Runoff pH and EC tell you what the roots are actually sitting in, which is the number that causes lockout.
Signs You Are Looking at Lockout
- Lower leaves yellowing while upper growth stays green.
- Interveinal chlorosis (yellow between green veins) on new or middle growth.
- Brown or rust-colored spots that appear on calcium-hungry growth.
- Purple or red stems and leaf edges tied to phosphorus uptake.
- Growth stalls even though feed strength has not changed.
- Runoff EC climbing run after run.
Common Causes of pH Drift
- Feeding at full strength every watering with no runoff.
- Mixing nutrients, then forgetting to pH the final solution.
- High-alkalinity tap water that pushes pH up after a day or two.
- Letting pots dry out completely, which concentrates salts near the roots.
- Reusing old medium without rinsing it.
- A pH pen that has not been calibrated in weeks.
How to Fix Nutrient Lockout, Step by Step
- Measure the pH and EC of your feed water and of the runoff.
- If runoff EC is high and runoff pH is low, you have salt buildup. Skip straight to flushing.
- Flush with pH-adjusted water at roughly two to three times the pot volume, or change the reservoir in hydro.
- Let the medium drain, and never leave pots sitting in the runoff.
- Re-check runoff 24 hours later. It should land closer to your target range.
- Resume feeding at about half strength, then build back up over the next week or two.
- Keep checking every few days until new growth comes in green and flat.
Flushing Without Drowning the Roots
Use room-temperature water adjusted to your medium's target pH. In soil and coco, pour slowly and let it run through rather than dumping it all at once. In hydro, drain and refill with a mild, correctly pH'd solution instead of plain water for more than a day. Damaged roots recover faster in a stable, slightly moist environment than in a soggy one.
Preventing Lockout on the Next Run
- Calibrate your pH pen every few weeks and store the probe in storage solution.
- Mix nutrients first, let the solution sit, then pH it right before watering.
- Water to a little runoff in containers so salts do not accumulate.
- Keep EC in a sensible range for the plant's stage instead of chasing the highest number.
- Avoid extreme wet and dry swings in the medium.
When It Is Not Lockout
Overwatering, root rot, cold root zones, light stress, and pests can all mimic a deficiency. If your runoff pH and EC look fine and leaves still decline, look at watering frequency, root health, and environment before you change the feed. New growth is the best measure of recovery, since damaged leaves will not turn green again.