Quick Answer

Magnesium deficiency shows as interveinal chlorosis on older, lower leaves first — the same pattern as iron deficiency but on old leaves, not new ones. This is the key distinction. Fix with magnesium sulfate (Epsom salt) at 0.5–1.0 g/litre, after confirming pH is correct.

Identifying Magnesium Deficiency

• Yellowing starts on older, lower leaves (not new growth)
• Yellow patches appear between green veins
• Leaves may eventually turn entirely yellow and drop
• Plant continues to grow but looks increasingly pale from bottom up

Causes

• Incomplete nutrient formula missing magnesium
• pH outside 5.5–6.5 blocking magnesium uptake
• Excess potassium or calcium competing with magnesium
• Long nutrient cycles without solution refresh

Fix

1. Check pH is in range 5.5–6.5.
2. Add magnesium sulfate (Epsom salt): estimated 0.5–1.0 g per litre as a starting point. Retest EC after adding.
3. For severe cases, foliar spray with 0.2% magnesium sulfate solution on leaf undersides.
4. Consider a full nutrient solution change if solution is old and mineral-imbalanced.

⚠️ Note: Dosing recommendations are estimates. Actual amount depends on your current magnesium level and nutrient product. Always retest EC and pH after adding any supplement.

Related Reading

• Yellow Leaves in Hydroponics
• Calcium Deficiency in Hydroponics
• Iron Deficiency in Hydroponics
• Nitrogen in Hydroponics