How do you recognize magnesium deficiency in plants?

Magnesium plays an important role for people, animals and plants and just like in the human body a magnesium deficiency in plants has major health consequences as for plants it plays a role in photosynthesis. Fortunately, a deficit is easily remedied in most cases.


Magnesium is very common on earth and an estimated 2% of the earth's crust is magnesium, but only in a bound form. These magnesium compounds mainly occur in seawater, salt basins and in old earth layers. Since magnesium also occurs in tap water, together with calcium it is responsible for the hardness of the water and thus the EC value.

What is the function of magnesium for the plant?

Magnesium is an element that is important for people and animals, but certainly for plants as well. In fact it is a building block for chlorophyll, the leaf green that gives the plant its green color. This chlorophyll plays an important role in photosynthesis and a magnesium deficiency in plants is also reflected in a reduced amount of leaf green granules, which makes the leaves turn yellow. In addition, magnesium fulfills the role of a cofactor in many plant processes, such as leaf formation.

How do you recognize the symptoms of a magnesium deficiency?

A magnesium deficiency in plants is a treacherous deficiency, since it is virtually unrecognizable during the first three to four weeks: the plant grows well and the leaves are healthy and green. The symptoms can only be recognized between weeks 4 and 6 of the growth. These manifest themselves in small rust-brown spots on the leaves under the later flowering part of the plant. This yellowing should not be confused with a nitrogen deficiency.

The striking thing about a magnesium deficiency is that especially the young leaves grow undiminished and stay healthy and green, while the older leaves are increasingly falling prey to the chlorosis and increasingly yellowing between the veins. Only in case of a severe deficiency do the younger leaves also get chlorosis. In a further stage, the spots can turn brown or even red.

Magnesium deficiency is relatively more common than other nutritional deficiencies but less in the culture on soil, since soil contains a relatively large amount of magnesium.

Causes of a magnesium deficiency in plants

The causes of a magnesium deficiency can be of a different nature, but in most cases a magnesium deficiency is the result of an incorrect ratio with other nutrients. An excess of potassium, ammonium and calcium in the substrate or in the nutrient solution ensures a reduced absorption of magnesium.

A low temperature of the substrate can also be a cause. This ensures a reduced metabolism and thus a reduced absorption of magnesium by the roots. An acidic soil environment can also be a cause of magnesium deficiency.

What can you do about a magnesium deficiency?

Fortunately, a magnesium deficiency is easily remedied in many cases. Preventively, measures can already be taken to this end by adding magnesium-based fertilizers to the nutrient water. Curatively, you can make a 2% magnesium sulfate solution with water and spray the plant with it. The fertilization with magnesium salts can be done via the root system.

To prevent a magnesium deficiency in plants, it is wise to opt for high-quality plant nutrition and to provide the plant with the right nutrients in both the growth phase and the flowering phase.