Why Magnesium Is Essential for Plant Health in Hydroponics

When we talk about plant health, photosynthesis is king. And at the heart of this vital process is magnesium—the central atom in the chlorophyll molecule. Without it, plants simply can’t capture light energy, and everything from growth to yield suffers.

Why Magnesium Matters in Plant Growth

Magnesium sits at the very centre of the chlorophyll molecule, surrounded by nitrogen, iron atoms, and a carbon matrix. It’s this structure that makes photosynthesis possible. Without magnesium, chlorophyll can’t function, leading to a failure in light absorption and energy transfer.

Key Role in Photosynthesis:

• Central atom in chlorophyll
• Facilitates energy transfer in plant cells
• Essential for light absorption and conversion into sugars

Symptoms of Magnesium Deficiency in Plants

Magnesium deficiency shows up as interveinal chlorosis—yellowing between the leaf veins while the veins remain green. This symptom is easiest to detect in broad-leaved plants (dicots) and harder to see in monocots like cereals and grasses.

Once these signs appear, it often means your plant is already stressed and yields could be compromised. Early prevention is key.

Look out for:

• Yellowing between veins
• Dark green veins on yellow leaves
• Poor growth or stunted plants

Causes of Magnesium Deficiency in Hydroponics and Soil

Even if you’re feeding your plants regularly, other factors might be blocking magnesium absorption:

1. Excess Calcium

In soil, high calcium levels—especially from using non-dolomitic lime—can outcompete magnesium for uptake.

Tip: Use dolomitic lime to ensure a proper balance of calcium and magnesium, or for soluble version a good ‘Cal-Mag‘ product. Cal-Mag products are designed to provide hydroponic crops with the right balance of these two macronutrients.

2. Too Much Potassium in Hydroponics

Hydroponic nutrient blends often contain high levels of potassium. When you stack multiple potassium-rich additives, magnesium gets locked out.

Solution: Balance your nutrients and avoid excessive additive stacking.

How to Treat and Prevent Magnesium Deficiency

If you suspect a magnesium deficiency, don’t panic. It’s treatable—especially in hydroponics.

Best Solutions:

• Epsom Salts (Magnesium Sulfate): Fast, effective, and affordable
• Cal-Mag Supplements: Provide a balanced ratio of calcium and magnesium
• Gold Leaf (Liquid Gold) Users: May still benefit from additional Cal-Mag for added insurance

Think of Cal-Mag as a safety net—a warm blanket or life jacket for your plants, ensuring crop quality doesn’t dip due to micronutrient imbalances.

When Magnesium Becomes Too Much

While rare in hydroponics, magnesium toxicity can occur in soils with high magnesium levels. This can also affect the uptake of other nutrients like calcium and potassium.

Products like liquid gypsum can help correct magnesium toxicity by improving calcium availability and soil structure.

Magnesium: A Secondary Macronutrient With Primary Importance

Alongside calcium and sulphur, magnesium is a secondary macronutrient. This means plants need it in relatively large amounts—just not quite as much as nitrogen, phosphorus, and potassium.

Don’t underestimate its importance. Without magnesium, your plants simply can’t photosynthesize effectively, no matter how much light, CO₂, or water they have.

Article by Dr Russell Sharp

If you would like to keep up to date with subjects just like this, you can listen to both our podcasts! Links can be found bellow:

Hydroponics Daily Podcast: https://open.spotify.com/show/207T7p7fw9sPjINfSjVXW2

Cereal Killers Podcast: https://t.co/eSEbBkTVHl