Magnesium (Mg) Deficiency

Scientific Name

Magnesium (Mg)

Atomic Number

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.

Container Nursery Stock, Pot & Bedding Plants

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.

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.

Foliar sprays or fertigation with soluble magnesium fertilizers such as:

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.

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.