Magnesium (Mg) Deficiency

Magnesium (Mg) Deficiency

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Scientific Name
Magnesium (Mg)
Atomic Number
12
Atomic Weight u
24.305
Elemental Group
Meso elements (Ca, Mg, S ) | Secondary macronutrients
Available Forms

Available forms of Magnesium (Mg) for Horticultural Production

  • Magnesium sulfate (MgSO₄·7H₂O, “Epsom salt”) – highly soluble; rapid correction via foliar sprays or substrate application.
  • Magnesium sulfate monohydrate (MgSO₄·H₂O) – more concentrated, soluble form of magnesium sulfate for substrate use.
  • Magnesium nitrate [Mg(NO₃)₂·6H₂O] – highly soluble; supplies both Mg and N; widely used in fertigation and foliar programs.
  • Dolomitic lime (CaMg(CO₃)₂, “Dolomite”) – slow-release; supplies both Ca and Mg while raising substrate pH.
  • Magnesium oxide (MgO) – slow-release, low solubility; often incorporated in granular or coated fertilizers.
  • Magnesium carbonate (MgCO₃) – moderately soluble; gradual Mg release; also contributes to pH adjustment.
  • Magnesium hydroxide (Mg(OH)₂) – slow-release source; used in specialty or controlled-release formulations.
  • Magnesium chloride (MgCl₂·6H₂O) – soluble; used occasionally in foliar sprays or hydroponic systems.
  • Magnesium chelates (Mg-EDTA, Mg-DTPA) – soluble; effective across a wider pH range; suitable for fertigation and foliar feeding.
  • Magnesium frits (varied composition, “Slow-release Mg frits”) – glass-fused carriers supplying Mg gradually in container mixes.

Magnesium (Mg) Deficiency

Container Nursery Stock, Pot & Bedding Plants

Symptoms

  • Interveinal chlorosis (yellowing between veins) appears first on older leaves because magnesium is mobile within the plant.
  • Leaf curl, mottling, necrotic spots, or marginal scorching may develop as deficiency progresses.
  • Premature leaf drop can occur in severe cases, often starting with older foliage.
  • Reduced growth, smaller leaves, stunting, and overall loss of plant vigor are common.
  • In some species, leaf margins may show reddish or purple tints or flowers may be smaller and less abundant.

Causes

  • Low Mg availability in substrate due to naturally low levels or insufficient fertilizer inputs.
  • Competing cations such as potassium (K), calcium (Ca), and ammonium (NH4+) reduce Mg uptake.
  • Acidic substrates (low pH) or sandy soils that leach nutrients readily.
  • Over-irrigation or heavy rainfall causing leaching of soluble Mg.
  • Use of Mg-deficient fertilizers or irrigation water.

Correction

Rapid relief

Foliar sprays or fertigation with soluble magnesium fertilizers such as:

  • Magnesium sulfate (MgSO4·7H2O, Epsom salt).
  • Magnesium nitrate [Mg(NO3)2·6H2O] for combined Mg and N supply.
Medium to long-term correction
  • Incorporate slow-release Mg sources like dolomitic lime (CaMg(CO3)2), magnesium oxide (MgO), or controlled-release Mg fertilizers into substrates.
  • Adjust substrate pH into the optimal range (typically 5.5–6.5) to improve availability.
  • Management practices: modify irrigation to minimize nutrient leaching; balance K:Mg and Ca:Mg ratios in fertilization programs.

Prevention

  • Routine monitoring: test growing media and irrigation water for Mg content and pH.
  • Balanced nutrition: use complete fertilizers containing magnesium; avoid overuse of K or Ca that antagonize Mg uptake.
  • Substrate preparation: include Mg sources (e.g., dolomitic lime, slow-release Mg fertilizers) at planting or potting.
  • Crop monitoring: inspect plants regularly for early chlorosis to enable prompt correction.
  • Irrigation management: avoid excessive leaching through overwatering or very frequent irrigation cycles.

Magnesium (Mg) Deficiency

Magnesium (Mg)
Scientific Name
Magnesium (Mg)
Atomic Number
12
Atomic Weight u
24.305
Elemental Group
Meso elements (Ca, Mg, S ) | Secondary macronutrients
Available Forms

Available forms of Magnesium (Mg) for Horticultural Production

  • Magnesium sulfate (MgSO₄·7H₂O, “Epsom salt”) – highly soluble; rapid correction via foliar sprays or substrate application.
  • Magnesium sulfate monohydrate (MgSO₄·H₂O) – more concentrated, soluble form of magnesium sulfate for substrate use.
  • Magnesium nitrate [Mg(NO₃)₂·6H₂O] – highly soluble; supplies both Mg and N; widely used in fertigation and foliar programs.
  • Dolomitic lime (CaMg(CO₃)₂, “Dolomite”) – slow-release; supplies both Ca and Mg while raising substrate pH.
  • Magnesium oxide (MgO) – slow-release, low solubility; often incorporated in granular or coated fertilizers.
  • Magnesium carbonate (MgCO₃) – moderately soluble; gradual Mg release; also contributes to pH adjustment.
  • Magnesium hydroxide (Mg(OH)₂) – slow-release source; used in specialty or controlled-release formulations.
  • Magnesium chloride (MgCl₂·6H₂O) – soluble; used occasionally in foliar sprays or hydroponic systems.
  • Magnesium chelates (Mg-EDTA, Mg-DTPA) – soluble; effective across a wider pH range; suitable for fertigation and foliar feeding.
  • Magnesium frits (varied composition, “Slow-release Mg frits”) – glass-fused carriers supplying Mg gradually in container mixes.
Magnesium (Mg) Deficiency
Image Source: Corn. Bak B.V. (NL), Everris Research (NL), LVG Bad Zwischenahn (D), PPO Boskoop (NL), USDA (USA), care of ICL

Magnesium (Mg) Deficiency

Container Nursery Stock, Pot & Bedding Plants

Symptoms

  • Interveinal chlorosis (yellowing between veins) appears first on older leaves because magnesium is mobile within the plant.
  • Leaf curl, mottling, necrotic spots, or marginal scorching may develop as deficiency progresses.
  • Premature leaf drop can occur in severe cases, often starting with older foliage.
  • Reduced growth, smaller leaves, stunting, and overall loss of plant vigor are common.
  • In some species, leaf margins may show reddish or purple tints or flowers may be smaller and less abundant.

Causes

  • Low Mg availability in substrate due to naturally low levels or insufficient fertilizer inputs.
  • Competing cations such as potassium (K), calcium (Ca), and ammonium (NH4+) reduce Mg uptake.
  • Acidic substrates (low pH) or sandy soils that leach nutrients readily.
  • Over-irrigation or heavy rainfall causing leaching of soluble Mg.
  • Use of Mg-deficient fertilizers or irrigation water.

Correction

Rapid relief

Foliar sprays or fertigation with soluble magnesium fertilizers such as:

  • Magnesium sulfate (MgSO4·7H2O, Epsom salt).
  • Magnesium nitrate [Mg(NO3)2·6H2O] for combined Mg and N supply.
Medium to long-term correction
  • Incorporate slow-release Mg sources like dolomitic lime (CaMg(CO3)2), magnesium oxide (MgO), or controlled-release Mg fertilizers into substrates.
  • Adjust substrate pH into the optimal range (typically 5.5–6.5) to improve availability.
  • Management practices: modify irrigation to minimize nutrient leaching; balance K:Mg and Ca:Mg ratios in fertilization programs.

Prevention

  • Routine monitoring: test growing media and irrigation water for Mg content and pH.
  • Balanced nutrition: use complete fertilizers containing magnesium; avoid overuse of K or Ca that antagonize Mg uptake.
  • Substrate preparation: include Mg sources (e.g., dolomitic lime, slow-release Mg fertilizers) at planting or potting.
  • Crop monitoring: inspect plants regularly for early chlorosis to enable prompt correction.
  • Irrigation management: avoid excessive leaching through overwatering or very frequent irrigation cycles.