Hydroponics Blog
Yellow Leaves in Hydroponics: Causes, Diagnosis, and Fixes
Quick Answer
Yellow leaves in hydroponics are most commonly caused by nitrogen deficiency (older leaves yellow first), iron deficiency (new growth yellows), pH out of range blocking nutrient uptake, or root damage. Check pH first — it solves 60% of yellowing cases.
Most Common Causes
| Symptom Pattern | Most Likely Cause | First Check |
|---|---|---|
| Old leaves yellow first, then newer | Nitrogen deficiency | EC too low, check ppm |
| New leaves yellow, veins stay green | Iron deficiency (chlorosis) | pH above 6.5 locks out iron |
| Yellow between leaf veins, all leaves | Magnesium deficiency | Check Mg in nutrient mix |
| Entire plant yellowing, wilting | Root rot or oxygen starvation | Check roots and DO levels |
| Yellow tips, margins | Nutrient burn or pH swing | Check EC and pH |
| Lower leaves drop and yellow | Natural senescence or nitrogen | Normal if only lowest leaves |
Step-by-Step Diagnosis
- Check pH first. Test your reservoir. Target 5.5–6.5 for most crops. pH drift above 6.8 locks out iron and manganese immediately.
- Check EC. If EC is below 1.0 mS/cm, nutrient starvation is the cause. If above 3.5, you may have nutrient toxicity.
- Look at which leaves are affected. New growth = micronutrient lockout (iron, manganese, zinc). Old growth = nitrogen, magnesium, phosphorus.
- Check roots. Pull a plant. Roots should be white or light tan. Brown, slimy, or foul-smelling roots = root rot causing nutrient block.
- Check reservoir temperature. Above 24°C reduces dissolved oxygen and promotes root disease. Critical in UAE summers.
Region Note: UAE and Desert Climates
In UAE summers, reservoir temperatures above 28°C are the leading cause of root damage and subsequent yellowing — even when pH and EC are correct. If temperatures are the issue, a reservoir chiller or deep insulated reservoir is the fix, not nutrient adjustment.
Fixes by Cause
- pH problem: Adjust pH to 5.8–6.2 and recheck in 24 hours. Do not over-correct.
- Nitrogen deficiency: Increase nutrient solution strength gradually. Do not jump EC by more than 0.3 mS/cm per day.
- Iron chlorosis: Lower pH to 5.8–6.0. Use chelated iron (EDTA below 6.5, EDDHA above 6.5).
- Root rot: Lower reservoir temperature, increase aeration, remove affected roots, treat with hydrogen peroxide (3ml of 3% per litre) or beneficial bacteria.
Common Mistakes
- Adding more nutrients without checking pH first — this makes the problem worse.
- Diagnosing from leaf colour alone without measuring EC and pH.
- Ignoring reservoir temperature in warm climates.
Related tools: Use the EC Calculator and pH Calculator to check and adjust your solution.