What Is Magnesium?

Magnesium (Mg) is one of the most abundant elements in our environment. It plays an essential role in many physiological processes, including muscle contraction, heart beat, nerve transmission and blood clotting. Mg is found naturally in the earth’s crust; however it becomes scarce during periods of drought or other environmental stressors such as volcanic eruptions or nuclear war. Because of its importance, humans have been extracting Mg from rocks and minerals since prehistoric times.

The first known use of magnesium was in the form of an antacid called “magnesia.” Magnesium sulfate is still used today as a common household additive. Magnesium carbonate is widely available over the counter in health food stores and pharmacies. Magnesium oxide is also commonly available and used in some toothpastes.

How Does Magnesium Affect Plants?

In order to grow properly, plants need Mg. They are unable to produce their own Mg without adequate amounts of water and nutrients. When there is insufficient Mg in the soil, plants cannot absorb enough water or nutrients from the soil to make up for the deficit. Without sufficient moisture and nutrients, plant growth slows down or stops altogether. This can be devastating during the flowering and fruiting stages of growth.

What Are the Signs of Magnesium Deficiency?

Magnesium deficiencies cause the older leaves on the bottom of the plant to change color. These leaves will typically develop a yellow hue and then eventually fall off. New “pup” leaves will then start to appear between the older leaves and the stem. These new growths are generally much smaller than normal.

What is Magnesium Toxicity?

There are no known cases of Mg toxicity in plants.

What Is the Best Way to Add Magnesium to Soil?

The best way to ensure adequate Mg levels in your soil is to buy an Mg supplement or mix your own. Many people use Epsom salt because it is cheap and readily available at most grocery or drug stores. Simply mix one tablespoon of Epsom salt per gallon of water. Pour this mixture on your soil every five to seven days. If using Epsom salt without mixing it with water, use at the rate of one teaspoon per gallon of soil.

It is important to note that if you live in hard water area (i.e. most places with city water), you should not apply Mg to your soil until at least a week after watering because the magnesium reacts negatively with hard water and will not be absorbed by the plants.

Another way to supply Mg to your plants is to buy a commercial Mg supplement. Some of the most common ones available are: Mag-O-Sol, Magnesol, MG-16-4, and Midwestern Grow. Follow the package directions for application.

One hundred pounds of dolomitic lime will provide 100 lbs of magnesium to the soil. Most agricultural lime is dolomitic.

What Is the Effect of Light on Magnesium?

Magnesium is immobile in the soil, so there is no need to worry about whether or not plants that are grown in the shade take up less Mg.

Why Are Some Labels On Mg Supplements Written in Red?

The labels on Mg supplements are written in red ink because scientists used to believe that plants could not absorb Mg that was in the form of red oxide. This has since been disproven, but the practice persists.

What Materials Are Used to Make Mg Soil Amendments?

A common Mg soil amendment is sulfate of magnesia. The most common brand of this material is Oderite. Do not confuse this with the common table salt also called sodium sulfate or Glaubers Salt.

How Does Magnesium Compare to Calcium in Plants?

Calcium and magnesium are opposites in many ways. They are like matter and anti-matter. Calcium is essential for strong cell walls and cell division while Mg is needed for soft tissues and water absorption. They compete for the same uptake channels in the roots. Excess Ca without enough Mg will cause incomplete seed germination, stunted growth, and death. If there is too much Mg and not enough Ca, mature plants will produce offspring that are weak and sterile.

What About Other Soil Types?

Most of the information on Mg was obtained using potting soil so it is reasonable to assume that other soil types would have similar effects. The main difference seems to be in the degree of change. Sandy soil, for example, seems to loose Mg at a faster rate than other soil types.

What About Hydroponics?

The situation with hydroponics is even more interesting. One would think that hydroponics would eliminate the problem altogether because the soil is constantly being renewed. This is true to some degree, but studies have shown that even hydroponically grown plants can suffer from Mg depletion. The reason for this is that many hydroponic solutions do not provide sufficient amounts of Mg to begin with and the process by which the nutrients are recycled causes a greater than normal loss of Mg.

Is it Necessary to Use a Special Fertilizer When Growing With Hydroponics?

Many Mg fertilizers are available on the market. The most common types are sulfate of magnesia (Oderite) and magnesium nitrate. Most garden centers carry a variety of different brands.

Common misconceptions

As mentioned before, many hydroponic solutions do not provide sufficient amounts of Mg to plant life.

Sources & references used in this article:

Magnesium deficiency in plants: An urgent problem by W Guo, H Nazim, Z Liang, D Yang – The Crop Journal, 2016 – Elsevier

Magnesium: a forgotten element in crop production by I Cakmak, AM Yazici – Better crops, 2010 – ipni.net

Magnesium deficiency and high light intensity enhance activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase in bean leaves by I Cakmak, H Marschner – Plant physiology, 1992 – Am Soc Plant Biol

Effects of magnesium deficiency on photosynthesis and carbohydrate partitioning by N Farhat, A Elkhouni, W Zorrig, A Smaoui… – Acta physiologiae …, 2016 – Springer

Role of magnesium in carbon partitioning and alleviating photooxidative damage by I Cakmak, EA Kirkby – Physiologia plantarum, 2008 – Wiley Online Library

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