What's the Function of Magnesium (Mg) in Plants?

Written by Amir Tajer


Posted on November 29 2018

You may have more in common with plants than you think. Much like us, plants need a wide range of nutrients to stay healthy and we’ve mentioned time and time again about magnesium’s importance to our own wellbeing.

But magnesium is also a critical macronutrient for plant growth and health. It is a key element of the chlorophyll molecule – essential for photosynthesis.

Magnesium gives leaves their green hue and activates most plant enzymes needed for growth while contributing to protein synthesis.

This is merely the surface of how magnesium benefits your plants. However, it is easy for something to go amiss in your garden if this macronutrient is lacking.

How Does Magnesium Function in Plants?

Within the world of plant health are different tiers of nutrients that work together to help your plants function at their best. These are:

Primary Nutrients: essential elements needed in large quantities. These include Nitrogen, Phosphorus and Potassium (NPK).

Secondary Nutrients: essential elements needed in moderate quantities. These include Magnesium, Sulfur and Calcium.

Micronutrients: essential elements needed in smaller quantities. These include Boron, Chlorine, Copper, Iron, Manganese, Molybdenum, Zinc.

While magnesium is a secondary nutrient, it does not mean it is any less important. It simply means your plants don't need as much of it compared to primary nutrients.

In fact, if your plants do not receive the moderate amounts of magnesium they crave, they may experience some serious symptoms.

What Are the Symptoms of Magnesium Deficiency?

Magnesium deficiency is common in light soils or those lacking organic matter. Magnesium is water soluble and is often leached from plants by heavy rains.

Some of the first symptoms include:

  • Interveinal Chlorosis that causes leaves to yellow while its veins remain green.



  • Leaf margins turn a reddish-brown or purple in color.



Magnesium is mobile in plants, and when there is a deficiency, chlorophyll in older leaves breaks down and transports to new leaves. Therefore chlorosis manifests in older leaves first.

If this deficiency is not corrected, this results in:

  • Leaf necrosis
  • Dropping of older leaves
  • Slow growth


How Do You Correct a Magnesium Deficiency? 

Fortunately, correcting a magnesium deficiency is not difficult if caught in its early stages. All you need is a magnesium-rich fertilizer, but also one that suits your soil’s pH level.

This is because of the link between the amount of magnesium in your soil and its pH level - the more magnesium the higher the pH level. And the wrong pH level can be detrimental for certain plants.

Keeping your soil’s pH level in mind, below are a few products you can try:

1. Magnesium Sulfate (Epsom Salt)


Adds: Magnesium

pH Level: Neutral – will not raise or lower current pH levels of soil.

2. Dolomite

Adds: Magnesium and Calcium

pH Level: Basic – will raise current pH levels of soil.

3. Sulfate of Potash Magnesia (K-Mag)


Adds: Magnesium, Soluble Potash and Sulfur

pH Level: Neutral – will not raise or lower current pH levels of soil.

4. Cal-Mag


Adds: Magnesium and Calcium

pH Level: Neutral – will not raise or lower current pH levels of soil.

5. Organic Compost

Adds: Depends on the organic matter used

pH Level: Depends on the organic matter used

When it comes to correcting a magnesium deficiency, or any nutrient deficiency in your plants, conducting a soil analysis is always the best bet.

A soil test removes the guesswork by telling you what nutrients your soil lacks and its current pH level so you can be sure to add what your soil needs and leave out what it doesn’t.

Shop our magnesium rich products above and your plants will be better off for it.


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