Problem Identifier / Magnesium Deficiency in Plants

How To Fix A Magnesium Deficiency In Plants

Magnesium Deficiency
Leaf of Feijoa tree (Acca sellowiana) with symptoms of magnesium deficiency.

Magnesium is a nutrient that enables plants to move the mineral between old and new leaves. A magnesium deficiency in plants can advance quickly, resulting in the loss of lower leaves. One of the most important growth elements is magnesium because it is at the center of the chlorophyll molecule within the tissue. This means if there is a deficiency, the chlorophyll shortage leads to stunted and poor plant growth.

Magnesium is necessary for the activation of certain enzyme systems. Enzymes are complicated substances responsible for building, modifying or breaking down compounds for the metabolism of the plant. This is one of the 13 nutrients located in the soil. When the plant is watered, the roots absorb the magnesium. Plants require magnesium to obtain energy from the sun required for photosynthesis to achieve a green coloration. Plants use magnesium to metabolize carbohydrates, and for stabilizing the cell membrane.

How Does a Magnesium Deficiency Affect the Quality of Your Plant?

The quality of the plant is affected in numerous ways including:

  • Yellowing on the edges of the leaves
  • Interveinal chlorosis
  • Dark, reddish stems or purple spots on new leaves
  • Decrease in growth

A magnesium deficiency is most common in agricultural soil but is also seen in weathered, acidic, strongly leached and sandy soil. Recognizing this deficiency is difficult, but it first appears on the older and lower leaves. The impact on plant quality is easier to see on the leaves exposed to direct light because they have more symptoms.

The growth of the plant slows, leaves have a yellow coloration on the edges, and interveinal chlorosis often develops. New leaves are usually yellow with reddish, purple or dark spots.

Plant Magnesium Deficiency Symptoms

Magnesium Deficiency in Plant
Magnesium deficiency caused by low pH in a Juniper. PHOTO CREDIT Mary Ann Hansen, Virginia Polytechnic Institute and State University,

Here are the main symptoms associated with a magnesium deficiency in plants:

  • Yellow areas between the leaf veins
  • Necrosis
  • Defoliation of lower leaves
  • Reduced fruit yields
  • Purpling areas on tomato plants

Due to the mobility of magnesium, the symptoms of deficiency are first seen on the lower leaves. The symptoms are the severest on these leaves because the plant moves magnesium to the new leaves to help with growth. The areas between the leaf veins become yellow, with the older leaves losing all green coloration except for the veins.

Interveinal chlorosis can result in the death of the plant tissue in the areas affected. The areas impacted on tomato leaves turn purple with defoliation of lower leaves. A magnesium deficiency in plants will not impact the fruit, but if the issue is severe, the plants become stressed leading to a decreased yield.

Possible Confusion with Other Symptoms

  • Dark spots on the leaves can be mistaken for a calcium deficiency
  • Leafhoppers leave dark spots on the leaves
  • Manganese deficiency results in dark spots and yellow areas between the leaf veins
  • Fluctuations in pH levels can leave spots on the leaves

What Causes a Magnesium Deficiency?

  • Supplementing plants with products containing calcium but no magnesium
  • Shortage of magnesium in the soil
  • Excessive use of fertilizers rich in potassium

A magnesium deficiency can occur when the plants are supplemented with a product or soil containing calcium but not magnesium including eggshells and agricultural lime. Magnesium is required for plants to access the energy provided by the sun to complete photosynthesis.

A magnesium deficiency is more common for plants grown in sandy or light soils. Excessive use of fertilizers rich in potassium often causes a deficiency since plants will absorb potassium before magnesium.

How to Fix a Magnesium Deficiency in Plants

Cannabis Magnesium Deficiency
Magnesium deficiency in a cannabis plant. Note the purple stalks.

Even if you are using soil high in nutrients, a magnesium deficiency can develop due to a low pH level at the plant roots. A low level prevents plants from absorbing magnesium. The correct pH must be maintained for the health of the plant. Using water without calcium causes a magnesium deficiency in plants but can be corrected by supplementation with regular nutrients including magnesium and calcium.

Once you have handled the issue, watch the plants closely for signs of deficiency recovery. The correct pH level is dependent on the growing medium, with the recommendation generally between 6.0 and 7.0. The pH level must remain 6.0 or higher for the plant roots to efficiently absorb magnesium. Flushing the growing medium with pH water helps restore the correct levels.

When a plant is deficient in magnesium, it is often lacking in calcium as well. You can treat a deficiency by purchasing supplements containing calcium and magnesium called Cal-Mag. Plants watered manually should be flushed with pH water containing all the essential nutrients. The level for hydroponically grown plants can be checked through the reservoir. Both the PPM and pH levels should be checked.

If the pH levels are too far off, the reservoir needs to be drained prior to refilling with fresh, pH’ed nutrients. You can mix one gallon of water with one teaspoon of Epsom salt for watering the plants since Epsom salt is almost entirely made from magnesium.

Magnesium Deficiency
Magnesium deficiency in Henry anise tree. PHOTO CREDIT John Ruter, University of Georgia,

The best ways to handle a magnesium deficiency in plants include:

  • Maintain the correct pH level for the roots
  • Supplement plants with nutrients including magnesium and calcium
  • Watch the plants for signs of deficiency recovery
  • Flush the growing medium with pH water
  • Check the PPM level in hydroponically grown plants
  • Drain the reservoir and refill with fresh nutrients
  • Add a mixture of water and Epsom salt

How Long Does It Take for a Plant to Recover from a Magnesium Deficiency?

Once you have taken care of the magnesium deficiency, discoloration and yellowing of the leaves should discontinue almost immediately. Even if the impacted areas do not completely recover, watch the plants to be certain the issue is not spreading. The magnesium deficiency should be gone within just a few days.

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