Quick Answer

Iron deficiency in hydroponics shows as interveinal chlorosis on new leaves — leaves turn yellow while veins stay green. The most common cause is pH above 6.5 locking out iron, not a lack of iron in the solution. Fix by lowering pH to 5.8–6.2 before adding more iron.

How to Identify Iron Deficiency

• New, young leaves turn yellow first (not old leaves — that is nitrogen)
• Veins remain green, tissue between them turns pale yellow
• Symptoms appear on growth tips and newest leaves
• Stems may appear pale or light green

Causes

• pH above 6.5 — iron becomes unavailable at higher pH. This is the most common cause by far.
• Wrong type of chelated iron — EDTA chelate is only stable up to pH 6.5. Above that, use EDDHA chelate.
• Iron not in nutrient formula — some incomplete formulas omit iron.
• Excess phosphorus or manganese — can compete with iron uptake.
• Cold water temperature — slows nutrient uptake including iron.

Fix

1. Test and correct pH first. Lower to 5.8–6.2. In most cases this alone resolves the deficiency within a few days.
2. Check your chelate type. If running pH 6.0–6.5, EDTA works. If above 6.5 was common in your system, switch to EDDHA.
3. Confirm iron is in your nutrient solution. Use a complete formula that lists iron (Fe) on the label.
4. Do not over-add iron. Iron toxicity causes brown spotting and root damage.

Related Reading

• Yellow Leaves in Hydroponics
• Magnesium Deficiency in Hydroponics
• pH Drift in Hydroponics
• Nitrogen in Hydroponics